In this work, we build on and use the outcome of an earlier study on topic identification in an algorithmically constructed publication-level classification (ACPLC), and address the issue of how to algorithmically obtain a classification of topics (containing articles), where the classes of the classification correspond to specialties. The methodology we propose, which is similar to that used in the earlier study, uses journals and their articles to construct a baseline classification. The underlying assumption of our approach is that journals of a particular size and focus have a scope that corresponds to specialties. By measuring the similarity between (1) the baseline classification and (2) multiple classifications obtained by topic clustering and using different values of a resolution parameter, we have identified a best performing ACPLC. In two case studies, we could identify the subject foci of the specialties involved, and the subject foci of specialties were relatively easy to distinguish. Further, the class size variation regarding the best performing ACPLC is moderate, and only a small proportion of the articles belong to very small classes. For these reasons, we conclude that the proposed methodology is suitable for determining the specialty granularity level of an ACPLC.

In a recent article we proposed a methodology for identification of research topics in an algorithmically constructed publication-level classification of research publications (ACPLC; Sjögårde & Ahlgren, 2018). We used a large dataset of more than 30 million publications in Web of Science to create an ACPLC, at the granularity level of topics. We consider topics as problem areas addressed by researchers, representing “an underlying semantic theme” (Yan et al., 2012), and we see topics as the lowest level of aggregation to be considered for classification of subject areas (Besselaar & Heimeriks, 2006). However, more levels of different granularity are needed for an ACPLC to be used to answer a broader range of questions. In the present study, we use a similar methodology to create a classification whose granularity corresponds to research specialties. In the remainder of this paper, we use the term “specialty” instead of “research specialty.” In short, a specialty is a “network of researchers who tend to study the same research topics” (Morris & Van der Veer Martens, 2008). However, the specialty notion is further discussed below. In this paper we identify the publications belonging to specialties by grouping the topics obtained in the previous study.

The identification of specialties is part of a broader aim to develop a standard approach to create a large and global hierarchical ACPLC of research publications in terms of geographical uptake, coverage of subject areas, and citation databases, such as Web of Science or Scopus. An ACPLC can be used for a great variety of analytical purposes and is especially useful for recurrent analytical activities.

A classification system that groups publications into classes whose sizes correspond to specialties can be used to study the publication output of different actors within a specialty; the collaboration between actors, dynamics, emergence and decline of specialties; and the relation between specialties. Moreover, a hierarchical classification, including both classes corresponding to topics and classes corresponding to specialties, makes it possible to identify topics within a specialty and, for example, a shifting focus of a specialty. We therefore suggest that the level of specialties, together with the level of topics, should be included in a standard ACPLC, and that such an ACPLC should be hierarchical.

The purpose of this paper is to find a theoretically grounded, practically applicable, and useful granularity level of an ACPLC with respect to specialties. To determine the granularity of specialties, a baseline classification is constructed. A set of journals is identified and used to create a baseline classification. ACPLCs with different granularities, constructed by the use of different values of a resolution parameter, are then compared to the baseline classification. The classification that best fits the baseline classification is proposed to be used for bibliometric analyses of specialties. In contrast to earlier work, our aim is to create a classification of publications that can be used to identify all specialties represented in Web of Science from 1980 onwards.

The remainder of this paper is structured as follows. In the next section, a short summary of our previous article on topic identification is given. The framework of the study is outlined in Section 3 and the specialty notion is discussed in Section 4. Data and methods are presented in Section 5, and Section 6 gives the results. Conclusions are given in Section 7.

To give the reader some background to the present study, in this section we summarize the earlier study on topic identification (Sjögårde & Ahlgren, 2018). In that study, we discussed how the resolution parameter given to the software Modularity Optimizer can be calibrated to obtain publication classes corresponding to the size of topics.

A set of about 31 million articles and reviews from Bibmet, KTH Royal Institute of Technology’s bibliometric database, which contains Web of Science data, was used for the study. The study involved a methodology consisting of four steps. In the first step, we constructed a baseline classification (BCPt) corresponding to topics, where BCPt contains synthesis articles, operationalized as articles with at least 100 references. Each such article constitutes a class, and its list of cited references points to the reference articles of the class (i.e., to the members of the class). The underlying assumption of this approach is that synthesis publications in general address a topic.

In the second step of the methodology, several ACPLCs of different granularity with respect to the topic level were created by setting the resolution parameter of Modularity Optimizer to different values. Normalized direct citation values between the articles in the dataset were used, as proposed by Waltman and van Eck (2012). For the third step, classifications derived from the ACPLCs were obtained, where each derived classification constitutes a classification of the union of the classes of the baseline classification, BCPt. Thus, the latter classification and a given derived one have exactly the same underlying reference articles. In the fourth and final step of the methodology, the similarity between BCPt and each of the derived classifications from the third step was quantified. For this purpose, the Adjusted Rand Index (ARI; Hubert & Arabie, 1985) was used. We denoted the ACPLC such that its corresponding derived classification exhibited the largest ARI similarity with BCPt by ACPLCt.

With respect to the results of the study, the class size variation regarding ACPLCt turned out to be moderate, and only a small proportion of the articles belong to very small classes. Moreover, the outcomes of two case studies showed that the topics of the cases were closely associated with different classes of ACPLCt, and that these classes tend to treat only one topic. We concluded that the proposed methodology is suitable to determine the topic granularity level of an ACPLC and that the ACPLC identified by this methodology is useful for bibliometric analyses.

In the present study, we use a similar methodology to identify specialties. The 230,559 classes obtained in the previous study, of which 136,939 have a size of at least 50 articles, are clustered into specialties. A baseline classification is constructed that corresponds to specialties, and a set of journals is used to create the baseline classification.

We need to point out that there is a substantial overlap between our earlier paper (Sjögårde & Ahlgren, 2018) and the present one. The reason for this is that the four-step methodology used in the earlier study, and briefly described above, is also used in the study underlying the present paper.

As in the previous study, we use a network-based approach to obtain a classification of research publications (Fortunato, 2010). We use the Modularity Optimizer1 software, created by Waltman and van Eck (2013), and the methodology put forward in Waltman and van Eck (2012). This framework has also been used by others (Klavans & Boyack, 2017a, b). The alternative modularity function is used (Traag et al., 2011), together with the SLM algorithm for modularity optimization. We acknowledge that a new algorithm for modularity optimization has been proposed (Traag et al., 2019). However, to be consistent with the previous study, we use the SLM algorithm in this study. We choose direct citation to express publication-publication relations, rather than bibliographic coupling (Kessler, 1965), cocitations (e.g., Marshakova-Shaikevich, 1973; Small, 1974), textual similarity (e.g., Ahlgren & Colliander, 2009; Boyack et al., 2011), or combined approaches (e.g., Colliander, 2015; Glänzel & Thijs, 2017). Direct citation is more efficient as it gives rise to fewer relations than the mentioned approaches, and there is empirical support that direct citations perform well in comparison with bibliographic coupling and cocitations when it comes to larger data sets (Boyack, 2017).

In Sjögårde and Ahlgren (2018), a network model with two levels of hierarchy, topics and specialties, was presented. This model comprises a logical classification: Each publication is classified into exactly one class at each level of hierarchy.2 Moreover, all publications in a class, at a level below the top level, are classified into exactly one and the same parent class. It follows that each topic in the model belongs to exactly one specialty. In this study, in which we continue to use logical classifications, we obtain such a relation by clustering topics into specialties, rather than using the alternative approach to cluster publications directly into specialties. Logical classifications have some shortcomings: Topics can be addressed by several specialties (Yan et al., 2012) or, at a higher level of aggregation, disciplines (Wen et al., 2017), phenomena not expressed by logical classifications. However, the relation between a topic and other specialties than the parent specialty, as well as relations between topics, can still be expressed and analyzed by use of the relational strengths associated with the edges in the model.

For further discussion on the general classification framework and for an explication of a model that expresses the relations between classes at different hierarchical levels in the model, we refer the reader to Sjögårde and Ahlgren (2018).

Specialties have been studied since the 1960s in the field of sociology. In this literature, specialties are considered as smaller intellectual units within research disciplines (Chubin, 1976). The researchers within the same specialty communicate with each other. They possess similar competences and can engage in the same, or similar, research problems (Hagstrom, 1970). The notion of specialties is closely related to the notion of invisible colleges (Crane, 1972; Price, 1965). However, as pointed out by Morris and van der Veer Martens (2008), invisible colleges “presuppose that the researchers are in frequent informal contact with one another,” which is not the case for specialties.

We use the definition of a specialty that has been given by Morris and van der Veer Martens (2008). They define a specialty as “a self-organized network of researchers who tend to study the same research topics, attend the same conferences, read and cite each other’s research papers and publish in the same journals.” Further, and in concurrence with others, we consider specialties to be the largest homogeneous units of science “in that each specialty has its own set of problems, a core of researchers, shared knowledge, a vocabulary, and literature” (Scharnhorst et al., 2012) and that they “play an important role in the creation and validation of new knowledge” (Colliander, 2014).

As early as 1974, Small and Griffith argued that publications can be clustered and that the obtained clusters may represent specialties (Small & Griffith, 1974). The single-linkage method was used by Small and Griffith to cluster 1,832 publications, which today would be considered a very small number of publications. They used their results to identify specialties. Since the 1970s, the technological advancements and the emergence of the Internet have changed the preconditions for research communication. There has also been a growth in research activity and production of research publications.

More lately, specialties have been identified and analyzed by the use of different clustering techniques (Lucio-Arias & Leydesdorff, 2009; Morris & van der Veer Martens, 2008; Scharnhorst et al., 2012). Different points of departure and different operationalizations of the specialty notion have captured different aspects of specialties. For example, clustering of publications based on citation relations and clustering of researchers based on coauthorship may result in different pictures of a specialty. The former approach identifies a set of publications and the latter a group of researchers belonging to a specialty. We attempt to capture the publications belonging to each specialty, rather than the researchers belonging to the specialty. A researcher can be part of several specialties, a property that cannot be expressed by the coauthorship approach. For this reason, we consider this approach less suitable for the identification of publications belonging to a specialty. We believe that it is preferable to base classifications constructed for the purpose of bibliometric analyses of specialties on the network of publications, rather than on the network of researchers. Our approach makes it possible to identify the researchers within a specialty without forcing every researcher into exactly one specialty. It also makes it possible to analyze the contribution of one researcher to multiple specialties.

Kuhn (1996) estimates the number of core researchers in a specialty to be around 100. Based on Lotka’s law (1926), Morris (2005) estimates the total number of researchers within a specialty to be around 1,000, and the number of publications produced by a specialty to be between 100 and 5,000. Boyack et al. (2014) regard specialties to be “ranging from roughly a hundred to a thousand articles per year.” We acknowledge that the size of specialties in terms of publications may vary over time. Because the output of research publications has been growing the last decades, it is likely that the total size of specialties, in terms of number of publications, has been growing. Also, the yearly publication production of active specialties is likely to be on average larger today than 10 or 20 years ago. The size of specialties is an empirical question that we intend to shed light on in the present study.

As in Sjögårde and Ahlgren (2018), KTH Royal Institute of Technology’s bibliometric database Bibmet was used for the study. Bibmet contains Web of Science publications from the publication year 1980 onwards. In the present study, we use the same set of publications as in the earlier study. We denote this set, in agreement with the earlier study, by P. P consists of 30,669,365 publications of the two document types: “Article” and “Review.” In the remainder of this paper, we use the term “article” to refer to both articles and reviews.

### 5.1. Design of the Study

We attempt to find a granularity of an ACPLC, where the ACPLC is based on the articles in P, that corresponds to specialties. In order to identify the granularity of specialties, a baseline classification of publications (BCP) is created. The BCP is a set of journals, considered as classes, and each member of a class in BCP is a publication appearing in the class (i.e., appearing in the journal).

The BCP is compared to several ACPLCs with different granularities, where each such ACPLC is obtained by clustering the classes of ACPLCt (see Section 2), which is thereby utilized in the present study. An appropriate granularity is detected and an ACPLC is chosen, the classes of which correspond to specialties. The methodology, which has four steps and a high degree of similarity with the methodology proposed in Sjögårde and Ahlgren (2018), is described in detail in steps I to IV below and schematically illustrated in Figure 1.

Figure 1.

Illustration of the design of the study.

Figure 1.

Illustration of the design of the study.

Close modal

#### I. Creation of baseline classes

We construct a baseline classification to correspond to specialties, which we denote by BCPs. For the creation of BCPs, a subset of journals covered by Web of Science is used. Each journal constitutes a class, and the publications appearing in the journal are the members of the class.

The reason for using journals to obtain BCPs is that researchers within a specialty publish in and read the same journals. The new possibilities to search, retrieve and read research articles have changed the role of journals, but nevertheless many journals are still focused on specific areas of expertise and the researchers within those areas. Such journals aim to publish articles that are relevant to its audience. For example, we consider bibliometrics as a specialty within the discipline of library and information science, and the scope of the Journal of Informetrics as roughly targeting the specialty of bibliometrics. In resemblance with Bradford’s law (1948), researchers within a specialty need to go to several journals to find all the relevant articles within their specialty. The boundaries of a specialty are vague and fading rather than sharp. If we consider a journal, the scope of which roughly covers a specialty, a core set of the articles in such journal is likely to be of high relevance to the core audience of the journal. The researchers that belong to this core audience can be considered as the backbone of the specialty. The rest of the articles in the journal have a fading relevance to this specialty. Some of these articles will be of higher relevance to other specialties.

When creating BCPs, we attempt to delimit the set of journals to such journals that, regarding their size and scope, can be considered as proxies for specialties. As BCPs is to be used as a baseline to estimate the granularity of an ACPLC regarding specialties, the following three requirements should be addressed:

• A.

To be able to compare the classifications, the union of the classes in BCPs must be a subset of the union of the classes (i.e., the topics) in ACPLCt.

• B.

Ideally, each class (journal) in BCPs should address exactly one specialty.

• C.

Ideally, each pair of distinct classes (journals) should address different specialties.

Now, to satisfy point A, we kept, for a given journal, only articles (i.e., publications that are of the document types “Article” or “Review”) that are present in ACPLCt (i.e., having a classification at the topic level).

To deal with point B, we first delimited the publication period to five years, namely 2008–2012. By this operation, which resulted in 6,140,762 publications in 13,070 journals, the risk of including journals that, for instance, have shifted subject focus over time is lowered. In addition to dealing with point B, the choice of publications from publication years that have both incoming and outgoing citations can be assumed to have a stabilizing effect when these articles are being clustered, compared to more recent publications.

We then removed all journals belonging to the Web of Science subject category “Multidisciplinary Sciences,” because a journal in this category is clearly not focused on a single specialty. After this, 13,023 journals remained. Next, we considered the distribution of journals by size. Figure 2 shows the distribution limited to journals with less than or equal to 2,000 articles. A typical journal, with respect to size and modal interval as a measure of central tendency, published 90–100 articles from 2008 to 2012. By including journals between the 10th and 75th percentiles of the journal size distribution displayed in Figure 2, journals with 47–478 articles were included. With this journal size limitation, the risk to include journals addressing multiple specialties (or journals with a narrower scope than a specialty) is reduced. The limitation reduced the number of journals to 8,485.

Figure 2.

Number of journals per journal size for journals with 1 to 2,000 articles in 2008–2012.

Figure 2.

Number of journals per journal size for journals with 1 to 2,000 articles in 2008–2012.

Close modal

Finally, in order to further reduce the risk of including journals addressing multiple specialties, we took journal self-citations into account. The idea is that a one-specialty journal can be assumed to cite itself to a larger extent compared to a journal that covers two or more specialties, other things held constant. In the light of this, we required, for a journal to be included in BCPs, that the self-citation ratio (in %) should be at least 10.3 The journal set was reduced to 1,540 journals by this procedure. Some test runs with different values of the threshold were conducted. These runs showed that lower values of the threshold reduced the maximum ARI value (cf. step IV below), which indicates that lowering the threshold value results in broader, less focused journals. The threshold was set to include as many journals as possible and to keep the ARI value reasonably high.

Some of the measures taken to satisfy point B are also relevant for satisfying point C (which states that each pair of distinct classes should address different specialties), such as the limitation to the publication years 2008–2012. With the aim to further raise the possibilities of satisfying point C, we applied bibliographic coupling between journals. If two journals had an overlap of 8% or more regarding their active cited references, they were considered as specialty overlapping.4 This threshold was chosen after browsing the list of journal pairs sorted in descending order based on number of shared cited references. Based on journal titles, it is obvious that some journal pairs have an overlapping subject focus: for example, the two journals Higher Education and Studies in Higher Education (19% citation overlap). A threshold for the cited references overlap was chosen to include such apparent cases. In addition, test runs were conducted with different threshold values. Higher values resulted in lower maximum ARI values. For this reason, we tried to keep the threshold value as low as possible (without considering journals with nonoverlapping subject focus as specialty overlapping).

We grouped journals so that all journals that were directly or indirectly connected, by a cited reference overlap of 8% or more, were assigned the same group. For example, if journal j1 has a cited reference overlap of ≥ 8% with journal j2, and j2 has a cited reference overlap of ≥ 8% with j3, then j1, j2, and j3 are assigned to the same group. Note that j1 and j3 are assigned to the same group even if they do not have an active reference article overlap of ≥ 8%. Each obtained group of journals was considered as addressing the same specialty. One of the journals was then randomly selected from each group. After the execution of this procedure, 967 journals remained. This number is the number of journals (classes) in BCPs. We denote the union of the classes in BCPs as P′.

#### II. Creation of ACPLCs of different granularity with respect to the specialty level

In order to obtain ACPLCs of different granularity, the first step was to measure the relatedness between the classes (topics) of ACPLCt. We measured the relatedness as the average normalized direct citation value between the articles belonging to the two classes: If class C contains m articles and class Cn, the sum of the m × n normalized direct citation values between articles in C and articles in C′ was divided by m × n. In the second step, the generated class relatedness values were iteratively given as input to Modularity Optimizer to cluster the classes of ACPLCt, where the resolution parameter was set to different values in the iterations.5 By this, ACPLCs were created for comparison of similarity with BCPs. We denote the ACPLCs by ACPLC_1, …, ACPLC_k, where k is the number of created ACPLCs.

#### III. Creation of classifications derived from the ACPLCs

For each ACPLC_i (1 ≤ ik), a classification was derived from ACPLC_i in the following way:

• (a)

Each class C in ACPLC_i such that C did not contain any articles in P′ was removed from ACPLC_i. Let ACPLC_i1 be the subset of ACPLC_i that resulted from the removal.

• (b)

For each class C in ACPLC_i1, all articles in C that did not belong to P′ were removed from C. Let ACPLC_iP′ be the set that resulted from these removal operations.

Clearly, the set ACPLC_iP′ constitutes a classification of P′ (i.e., of the union of the classes of the baseline classification BCPs). Thus, ACPLC_iP′ and BCPs have exactly the same underlying articles. We denote the k derived classifications as ACPLC_1P′, …, ACPLC_kP′. These classifications then correspond to the classifications ACPLC_1, …, ACPLC_k.

#### IV. Quantification of the similarity between BCPs and the ACPLC_iP′s

We attempt to optimize the granularity of an ACPLC_iP′ so that it exhibits as high a similarity as possible with BCPs. Figure 3 illustrates the relation between two classifications as an alluvial diagram. Example A shows two classifications A1 and A2 with a high similarity. Example B shows two classifications where one of the classifications is more coarsely grained (B1) than the other classification (B2). The similarity between A1 and A2 is higher than the similarity between B1 and B2. If we consider B1 as a baseline classification, then the granularity of B2 would be too finely grained.

Figure 3.

Two alluvial diagrams (A and B) illustrating the relation between two classifications. A shows two classifications with a high level of similarity. B shows two classifications with a low level of similarity.

Figure 3.

Two alluvial diagrams (A and B) illustrating the relation between two classifications. A shows two classifications with a high level of similarity. B shows two classifications with a low level of similarity.

Close modal

As in our topic identification study, we used the ARI (Hubert & Arabie, 1985) to quantify the similarity between BCPs and an ACPLC_iP′. The ARI ranges from 0 to 1. It is advantageous over the original Rand Index proposed by Rand (1971), because it adjusts for chance. The ARI compares two classifications by considering pairs of items in one of the classifications and whether or not each pair is grouped into the same class in the other classification. Note that an ARI value of 1 between BCPt and an ACPLC_iP′ corresponds to a situation in which these two classifications are identical. For further information on ARI, we refer the reader to Sjögårde and Ahlgren (2018).

To find the ACPLC_iP′ with the highest ARI similarity with BCPs, we tested the similarity after each run of Modularity Optimizer. A first run was made with a resolution parameter value of 5E-7. This value was chosen based on previous experience and some testing. We then increased the parameter value by 5E-7. This increase resulted in a higher ARI similarity, and we therefore increased the resolution further by 5E-7 for the third run, from 1E-6 to 1.5E-6. We continued by increasing the resolution by 5E-7 in total four more times, and thus seven runs were done. The fifth run, with a resolution parameter value of 2.5E-6, gave rise to the highest ARI similarity (see Table 2 and Figure 4, Section 6).

Figure 4.

ARI values between ACPLC_iP′s and BCPs. The vertical axis shows the ARI value and the horizontal axis shows the value of the resolution parameter used to obtain the corresponding ACPLC_is. The order of ACPLC_iP′s corresponds to their order in Table 2.

Figure 4.

ARI values between ACPLC_iP′s and BCPs. The vertical axis shows the ARI value and the horizontal axis shows the value of the resolution parameter used to obtain the corresponding ACPLC_is. The order of ACPLC_iP′s corresponds to their order in Table 2.

Close modal

In total BCPs consists of 967 baseline classes. A given ACLPC_iP′ consists of 202,647 articles, which is about 3.3% of the articles from the years 2008–2012 in the corresponding ACPLC_i. The ACPLC_i such that ACLPC_iP′ exhibits the largest ARI similarity with BCPs is proposed to be used for the analyses of specialties. We denote this ACPLC_i by ACPLCs.

In this section, we first deal with the selection and properties of ACPLCs. Then, as in the earlier study on topic identification (Sjögårde & Ahlgren, 2018), we consider two cases. We examine the specialties of articles belonging to (1) the Web of Science subject category “Information science & Library Science,” and (2) the Web of Science subject category “Medical Informatics.”

### 6.1. Selection and Properties of ACPLCs

Figure 4 shows a scatterplot of the relation between the resolution value (horizontal axis) used to obtain ACPLC_is and the ARI value (vertical axis), obtained by comparing the ACPLC_iP′s with BCPs. ACPLC_5P′ has the highest ARI value. ACPLC_5P′ corresponds to ACPLC_5, which we consider to be the most proper ACPLC_i with respect to granularity of specialties. In the remainder of this paper, we denote ACPLC_5 as ACPLCs. However, we acknowledge that ACPLC_4P′ and ACPLC_6P′ have ARI values that are only slightly lower/higher than the value of ACPLC_5P′. Thus, ACPLC_4P′ and ACPLC_6P′ perform almost as well as ACPLC_5P′.

To get a picture of how well ACPLCs matches BCPs, we calculated the distribution of articles in an average class in BCPs into classes (journals) in ACPLCs. This was done by first calculating the average number of classes in ACPLCs into which the articles in a class in BCPs are distributed, an average that is equal to 50 (after rounding to the nearest integer). We then selected all 12 classes in BCPs that were distributed into exactly 50 classes. Let the set of these classes be Psc. The average number of articles in a Psc class is 160.3. For each of the Psc classes, we calculated the number of its articles in each of the 50 ACPLCs classes and sorted the resulting table in descending order. The ACPLCs class with the highest number of articles (i.e., the class corresponding to the first row in the table) was assigned rank 1, the second largest class (i.e., the class corresponding to the second row in the table) was assigned rank 2, etc. In this way, 12 ranked tables were obtained. Finally, averages of the number of articles by rank number, 1, …, 50, were calculated across all the 12 tables. Figure 5 shows the resulting average distribution of articles in Psc (to the left) into the 50 ACPLCs classes (to the right). Ranks and average number of articles across the Psc classes are shown for ACPLCs.

Figure 5.

Alluvial diagram for an average class. The diagram shows the distribution of journal articles in BCPs into ACPLCs.6

Figure 5.

Alluvial diagram for an average class. The diagram shows the distribution of journal articles in BCPs into ACPLCs.6

Close modal

Given that we consider the classes in ACPLCs as specialties, the distribution of journal articles in a typical BCPs class follows a skewed distribution of specialties. About 41% of the articles in an average BCPs class are distributed into the two most frequent specialties, and 34 specialties (classes 17 to 50) are represented by a single article (after rounding to nearest integer). Hence, a high share of the articles of the average BCPs class is concentrated to a few of the ACPLCs classes. We therefore consider the match between ACPLCs and BCPs as good.

ACPLCs consists of 61,805 classes, ranging from 1 to 46,078 articles. Most of the classes are small in size; however, these classes contain a small share of the total number of articles in ACPLCs. For instance, classes with fewer than 500 articles contain about 1.2% of the articles in ACPLCs. Figure 6 shows a histogram of the distribution of classes by class size (in terms of number of articles). In order to include classes of a substantial size in the figure, classes with fewer than 500 articles have been excluded from the figure.

Figure 6.

Histogram of number of classes by class size for ACPLCs. Classes with fewer than 500 articles disregarded.

Figure 6.

Histogram of number of classes by class size for ACPLCs. Classes with fewer than 500 articles disregarded.

Close modal

Most specialties of substantial size (minimum of 500 articles) have 5 (10th percentile) to 62 (90th percentile) subordinated topics of substantial size (a minimum of 50 articles), with a mode of 6, a median of 19 and a mean of about 28 (Figure 7 and Table 1).

Figure 7.

Histogram of number of specialties by number of subordinated topics for ACPLCs. Specialties with fewer than 500 articles and topics with fewer than 50 articles disregarded.

Figure 7.

Histogram of number of specialties by number of subordinated topics for ACPLCs. Specialties with fewer than 500 articles and topics with fewer than 50 articles disregarded.

Close modal
Table 1.
Distribution statistics of number of topics per specialty for ACPLCs. Specialties with fewer than 500 articles and topics with fewer than 50 articles disregarded
Mean # topics per specialtyMedian # topics per specialtyMode # topics per specialtyP10P90
27.6 19 62
Mean # topics per specialtyMedian # topics per specialtyMode # topics per specialtyP10P90
27.6 19 62

In Figure 8, class sizes are plotted by rank order for ACPLCs (= ACPLC_5), as well as for ACPLC_4 and ACPLC_6. A log-10 scale is used on both the vertical axis (showing class sizes by number of articles) and the horizontal axis (showing ranks). In this figure, all classes are shown, including small size classes. About 4,200 classes contain at least 1,000 articles, about 1,000 classes contain at least 10,000 articles and about 30 classes contain at least 30,000 articles. In agreement with our study on topics, the size of classes is dropping rather slowly, regardless of classification. The increasing granularity—from ACPLC_4 via ACPLCs to ACPLC_6—is reflected by, for example, corresponding, decreasing intercepts.

Figure 8.

Distribution of number of articles by class size for three classifications. The classes in ACPLC_3, ACPLC_4 = ACPLCs, and ACPLC_5 are ordered descending by size with respect to the horizontal axis. Log-10 scale used for both axes.

Figure 8.

Distribution of number of articles by class size for three classifications. The classes in ACPLC_3, ACPLC_4 = ACPLCs, and ACPLC_5 are ordered descending by size with respect to the horizontal axis. Log-10 scale used for both axes.

Close modal

Figure 9 expresses the number of articles in P (vertical axis) that is associated with different class sizes (horizontal axis). For a randomly selected article a, it is most probable that the size of the specialty class in ACPLCs to which a belongs is 6,000–7,000 articles (cf. the highest bar of the histogram in Figure 9). Eighty percent of the articles belong to classes consisting of 2,899 (10th percentile) to 22,819 (90th percentile) articles (Table 2). The median value of ACPLCs is 10,499 and the mean 12,016. This distribution is not as skewed as the corresponding topic distribution (Sjögårde & Ahlgren, 2018, Figure 8).

Figure 9.

Histogram of number of articles by class size for ACPLCs.

Figure 9.

Histogram of number of articles by class size for ACPLCs.

Close modal
Table 2.
For each ACPLC_iP′, the ARI value between ACPLC_iP′ and BCPs, and the value of the resolution parameter used to obtain ACPLC_i are shown, as well as number of classes with at least 500 articles and class size distribution measures for ACPLC_i
DenotationResolutionARI value# classes with # articles ≥ 500Weighted class size distribution measures regarding ACPLC_i (i = 1, …, 7): mean, median, 10th and 90th percentiles (denoted P10 and P90)
Mean # articles per classMedian # articles per classP10P90
ACPLC_1P′ 0.0000005 0.1385 881 66,750 57,984 19,552 121,981
ACPLC_2P′ 0.0000010 0.2010 1,888 31,123 27,377 8,866 59,985
ACPLC_3P′ 0.0000015 0.2157 2,953 20,426 17,960 5,260 39,326
ACPLC_4P′ 0.0000020 0.2208 3,969 15,228 13,145 3,765 29,509
ACPLC_5P′ 0.0000025 0.2209 4,897 12,016 10,499 2,899 22,819
ACPLC_6P′ 0.0000030 0.2195 5,770 9,936 8,589 2,342 18,655
ACPLC_7P′ 0.0000035 0.2163 6,604 8,564 7,429 1,900 16,351
DenotationResolutionARI value# classes with # articles ≥ 500Weighted class size distribution measures regarding ACPLC_i (i = 1, …, 7): mean, median, 10th and 90th percentiles (denoted P10 and P90)
Mean # articles per classMedian # articles per classP10P90
ACPLC_1P′ 0.0000005 0.1385 881 66,750 57,984 19,552 121,981
ACPLC_2P′ 0.0000010 0.2010 1,888 31,123 27,377 8,866 59,985
ACPLC_3P′ 0.0000015 0.2157 2,953 20,426 17,960 5,260 39,326
ACPLC_4P′ 0.0000020 0.2208 3,969 15,228 13,145 3,765 29,509
ACPLC_5P′ 0.0000025 0.2209 4,897 12,016 10,499 2,899 22,819
ACPLC_6P′ 0.0000030 0.2195 5,770 9,936 8,589 2,342 18,655
ACPLC_7P′ 0.0000035 0.2163 6,604 8,564 7,429 1,900 16,351

The number of articles contributing to a specialty in 2015 (the most recent complete year at the time for data extraction) is between 148 and 1,597, given that we only take the mid-80% of the distribution into account (Table 3 and Figure 10). The median class size is 593. The mean number of articles per specialty class is growing approximately linearly across the 10-year period (Table 3). This can be expected, considering the linear growth of research publications in Web of Science.

Table 3.
For a 10-year period (at the time for data extraction), the table shows class size distribution measures for ACPLCs
Publication year# ArticlesWeighted distribution measures regarding ACPLCs: mean, median, 10th and 90th percentiles (denoted P10 and P90)
Mean # articles per classMedian # articles per classP10P90
2006 989,420 438 366 98 869
2007 1,040,026 461 384 102 918
2008 1,115,118 497 415 111 974
2009 1,166,665 525 437 114 1,028
2010 1,210,495 555 454 118 1,109
2011 1,290,309 603 484 126 1,216
2012 1,358,175 647 516 132 1,302
2013 1,435,835 705 551 140 1,434
2014 1,478,273 749 572 144 1,513
2015 1,524,010 789 593 148 1,597
Publication year# ArticlesWeighted distribution measures regarding ACPLCs: mean, median, 10th and 90th percentiles (denoted P10 and P90)
Mean # articles per classMedian # articles per classP10P90
2006 989,420 438 366 98 869
2007 1,040,026 461 384 102 918
2008 1,115,118 497 415 111 974
2009 1,166,665 525 437 114 1,028
2010 1,210,495 555 454 118 1,109
2011 1,290,309 603 484 126 1,216
2012 1,358,175 647 516 132 1,302
2013 1,435,835 705 551 140 1,434
2014 1,478,273 749 572 144 1,513
2015 1,524,010 789 593 148 1,597
Figure 10.

Histogram of number of articles by class size for the publication year 2015 and for ACPLCs.

Figure 10.

Histogram of number of articles by class size for the publication year 2015 and for ACPLCs.

Close modal

As mentioned in the introduction, Morris (2005) estimates the size of specialties to be between 100 and 5,000 articles (but not mentioning any time period), and Boyack et al. (2014) estimate the yearly article output of a specialty to be somewhere between 100 and 1,000 articles. The results of the present study cannot be easily compared to these figures. The estimations of Morris and Boyack et al. are rough. Morris does not mention any time period. Further, the work by Morris is rather old and the size of specialties may have increased in terms of publication output. Table 3 shows that the number of articles in Web of Science has been growing by more than 50% between 2006 and 2015. In 2015, the size of specialties ranges from about 150 articles (10th percentile) to 1,600 (90th percentile) articles. Thus, the size of specialties in 2015 is about 50% larger than the size estimated by Boyack et al. We regard this difference as rather small, taking into account that Boyack et al. define the next larger level (disciplines) to range from tens to hundreds of thousands of articles per year, several orders of magnitude larger than our estimation of the size of specialties.

In agreement with Morris and Boyack et al., we find it reasonable not to consider publication classes under some threshold to be regarded as specialties. One solution to the problem of small class sizes is to reassign such classes (classes below a threshold) based on their relations with larger classes (classes above or equal to the same threshold) as proposed by Waltman and van Eck (2012). However, how to set the threshold is a question that we do not address in this paper.

### 6.2. The Case of Information Science & Library Science

To explore how articles within the discipline of library and information science (LIS) are distributed into classes in ACPLCs, we retrieved all articles in P that belong to a journal classified into the Web of Science subject category “Information Science & Library Science” and published in the period 2011–2015. In total, 16,278 articles were retrieved. Let Plis be this set of articles.

For each class in ACPLCs, labels were automatically created based on author keywords. Chi-square was used to quantify the relevance of author keywords in each class, and for each class, three author keywords with highest rank were concatenated to a label (for more detail see Sjögårde & Ahlgren, 2018). To distinguish the scope of each specialty, we used these labels and the labels of the topics in each class. Recall that ACPLCs is obtained by clustering the topics of ACPLCt, the best performing ACPLC with respect to topic identification (Sjögårde & Ahlgren, 2018).

Table 4 shows the total number of articles in the 10 most frequent specialties and the number, and the share, of articles in a specialty that belong to Plis. The top 10 specialties cover about 48% of the articles in Plis. Some of the top 10 specialties are highly concentrated within the analyzed Web of Science subject category (e.g., “INFORMATION LITERACY//PUBLIC LIBRARIES//ACADEMIC LIBRARIES,” 79%), whereas other specialties have a low share of its total number of articles in this category (e.g., “INNOVATION//PATENTS//OPEN INNOVATION,” 7%).

Table 4.
Distribution of articles in the Web of Science subject category “Information Science & Library Science” into specialties, 2011–2015
RankSpecialty# articles in PlisTotal # articles in specialtyShare of specialty in Plis
1 BIBLIOMETRICS//CITATION ANALYSIS//IMPACT FACTOR 1,867 4,486 42%
2 INFORMATION LITERACY//PUBLIC LIBRARIES//ACADEMIC LIBRARIES 1,635 2,068 79%
3 INTERLENDING//DOCUMENT DELIVERY//ACADEMIC LIBRARIES 1,243 1,759 71%
4 RECOMMENDER SYSTEMS//COLLABORATIVE FILTERING//INFORMATION RETRIEVAL 564 4,965 11%
5 ELECTRONIC HEALTH RECORDS//ELECTRONIC MEDICAL RECORD//MEDICAL INFORMATICS 494 3,724 13%
6 ENTERPRISE RESOURCE PLANNING//ENTERPRISE RESOURCE PLANNING ERP//END USER COMPUTING 484 1,481 33%
7 KNOWLEDGE MANAGEMENT//KNOWLEDGE SHARING//OPEN SOURCE SOFTWARE 457 1,439 32%
8 INNOVATION//PATENTS//OPEN INNOVATION 366 5,519 7%
9 UNIVERSAL SERVICE//TELECOMMUNICATIONS//ACCESS PRICING 326 1,219 27%
10 HEALTH LITERACY//INTERNET//MHEALTH 314 4,394 7%
RankSpecialty# articles in PlisTotal # articles in specialtyShare of specialty in Plis
1 BIBLIOMETRICS//CITATION ANALYSIS//IMPACT FACTOR 1,867 4,486 42%
2 INFORMATION LITERACY//PUBLIC LIBRARIES//ACADEMIC LIBRARIES 1,635 2,068 79%
3 INTERLENDING//DOCUMENT DELIVERY//ACADEMIC LIBRARIES 1,243 1,759 71%
4 RECOMMENDER SYSTEMS//COLLABORATIVE FILTERING//INFORMATION RETRIEVAL 564 4,965 11%
5 ELECTRONIC HEALTH RECORDS//ELECTRONIC MEDICAL RECORD//MEDICAL INFORMATICS 494 3,724 13%
6 ENTERPRISE RESOURCE PLANNING//ENTERPRISE RESOURCE PLANNING ERP//END USER COMPUTING 484 1,481 33%
7 KNOWLEDGE MANAGEMENT//KNOWLEDGE SHARING//OPEN SOURCE SOFTWARE 457 1,439 32%
8 INNOVATION//PATENTS//OPEN INNOVATION 366 5,519 7%
9 UNIVERSAL SERVICE//TELECOMMUNICATIONS//ACCESS PRICING 326 1,219 27%
10 HEALTH LITERACY//INTERNET//MHEALTH 314 4,394 7%

The highest ranked specialty, “BIBLIOMETRICS//CITATION ANALYSIS//IMPACT FACTOR,” focuses on bibliometric indicators, mapping and evaluation of research, and the analysis of scholarly communication. We acknowledge that a majority of the largest topics in this specialty are the same topics that were observed in the case study of Journal of Informetrics in the previous topics study (Sjögårde & Ahlgren, 2018, and  Appendix 1 in this paper). The second-ranked specialty, “INFORMATION LITERACY//PUBLIC LIBRARIES//ACADEMIC LIBRARIES,” focuses on library science. This category includes topics such as information literacy, knowledge organization, information practices and reference services. The specialty “INTERLENDING//DOCUMENT DELIVERY//ACADEMIC LIBRARIES” includes topics specifically related to academic libraries, such as electronic media, open access, interlending, library circulation systems and data repositories. The scopes of specialties 4, 6, 7, 8 and 10 are captured rather well by their labels, and these specialties are all clearly related to LIS. These five specialties include information retrieval, knowledge management, library and information aspects of health service and occupation as well as of innovation and patents. The specialty “ENTERPRISE RESOURCE PLANNING//ENTERPRISE RESOURCE PLANNING ERP//END USER COMPUTING” includes some topics related to LIS (e.g., IT business value, IT outsourcing, Information system planning, and Information infrastructure). The LIS relevance of “UNIVERSAL SERVICE//TELECOMMUNICATIONS//ACCESS PRICING” (rank 9) is within topics such as Internet access and Digital divide.

Appendix 1 lists the 10 topics with most publications in Plis for the top 10 ranked specialties with regard to Plis.

### 6.3. The Case of Medical Informatics (MI)

In analogy with the case of LIS, we retrieved all articles in P that belong to a Web of Science subject category, in this case “Medical Informatics,” and published in the period 2011–2015, to explore how articles within this discipline are distributed into classes in ACPLCs. In total, 12,516 articles were retrieved. Let Pmi be this set of articles.

Table 5 shows the top 10 specialties in Pmi, ranked by frequency. Only one specialty is highly concentrated into the “Medical Informatics” category, namely “ELECTRONIC HEALTH RECORDS//ELECTRONIC MEDICAL RECORD//MEDICAL INFORMATICS” (which is also present in the LIS case). For the rest of the top 10 specialties, 14% or less of the articles in the specialty belong to Pmi. This might suggest that MI is more interdisciplinary than LIS. It can also be the case that MI articles are published in broader journals, which are not classified into the “Medical Informatics” Web of Science subject category.

Table 5.
Distribution of articles in the Web of Science subject category “Medical Informatics” into specialties, 2011–2015
RankSpecialty# articles in PmiTotal # articles in specialtyShare of specialty in Pmi
1 ELECTRONIC HEALTH RECORDS//ELECTRONIC MEDICAL RECORD//MEDICAL INFORMATICS 1,548 3,724 42%
2 HEALTH LITERACY//INTERNET//MHEALTH 628 4,394 14%
3 HEALTH TECHNOLOGY ASSESSMENT//EQ 5D//PRIORITY SETTING 316 3,142 10%
4 ADAPTIVE DESIGN//INTERIM ANALYSIS//DOSE FINDING 297 2,094 14%
5 MISSING DATA//MULTIPLE IMPUTATION//GENERALIZED ESTIMATING EQUATIONS 288 2,530 11%
6 COMPETING RISKS//INTERVAL CENSORING//COUNTING PROCESS 286 2,278 13%
7 EVIDENCE-BASED MEDICINE//PUBLICATION BIAS//ABSTRACT 206 3,646 6%
8 PATIENT SAFETY//MEDICATION ERRORS//MEDICAL ERRORS 192 3,983 5%
9 TELEMEDICINE//TELEHEALTH//TELEPATHOLOGY 186 2,482 7%
10 CAUSAL INFERENCE//PROPENSITY SCORE//PRINCIPAL STRATIFICATION 141 1,545 9%
RankSpecialty# articles in PmiTotal # articles in specialtyShare of specialty in Pmi
1 ELECTRONIC HEALTH RECORDS//ELECTRONIC MEDICAL RECORD//MEDICAL INFORMATICS 1,548 3,724 42%
2 HEALTH LITERACY//INTERNET//MHEALTH 628 4,394 14%
3 HEALTH TECHNOLOGY ASSESSMENT//EQ 5D//PRIORITY SETTING 316 3,142 10%
4 ADAPTIVE DESIGN//INTERIM ANALYSIS//DOSE FINDING 297 2,094 14%
5 MISSING DATA//MULTIPLE IMPUTATION//GENERALIZED ESTIMATING EQUATIONS 288 2,530 11%
6 COMPETING RISKS//INTERVAL CENSORING//COUNTING PROCESS 286 2,278 13%
7 EVIDENCE-BASED MEDICINE//PUBLICATION BIAS//ABSTRACT 206 3,646 6%
8 PATIENT SAFETY//MEDICATION ERRORS//MEDICAL ERRORS 192 3,983 5%
9 TELEMEDICINE//TELEHEALTH//TELEPATHOLOGY 186 2,482 7%
10 CAUSAL INFERENCE//PROPENSITY SCORE//PRINCIPAL STRATIFICATION 141 1,545 9%

The largest specialty in the “Medical Informatics” category focuses on clinical decision support systems, clinical research informatics and electronic health records. The second-ranked specialty within the category, “HEALTH LITERACY//INTERNET//MHEALTH,” addresses topics within mobile health such as personal health records, online health information, and online support groups. The specialty “HEALTH TECHNOLOGY ASSESSMENT//EQ 5D//PRIORITY SETTING” focuses on health technology assessment and cost effectiveness.

The remaining seven top 10 ranked specialties have the following foci: (4) clinical trial designs; (5) mathematical and statistical models and methods within the medical sciences; (6) prediction and risk models; (7) evidence-based medicine, medical epistemology, meta-analysis methods, and literature searching; (8) Patient safety (includes incident and error reporting); (9) telehealth (can be seen as a predecessor to mobile health); and (10) gene ontologies.

Appendix 2 lists the 10 topics with most publications in Pmi for the top 10 ranked specialties with regard to Pmi.

In this study we have discussed how the resolution parameter given to the Modularity Optimizer software can be calibrated to cluster topics, obtained in a previous study on topic identification (Sjögårde & Ahlgren, 2018), so that the obtained publication classes correspond to the size of specialties. A set of journals has been used as baseline for the calibration. Journals were selected based on their size and self-citation rate. The underlying assumption of our approach is that journals of a particular size and focus have a scope that corresponds to specialties. By measuring the similarity between (1) the baseline classification and (2) multiple classifications obtained by using different values of the resolution parameter, we have identified a classification, which we denote as ACPLCs, whose granularity corresponds to specialties.

Some criteria for the evaluation of ACPLCt, the best performing ACPLC with respect to topic identification, are the same for the evaluation of ACPLCs. The differences in class sizes should not be too large and “the number of very small clusters should be minimized as much as possible” (Šubelj et al., 2016). In ACPLCs, 80% of the articles belong to classes consisting of 2,899–22,819 articles. Further, 80% of the articles belong to classes with a yearly publication rate of 98–869 articles in publication year 2006, increasing to 148–1,597 in the publication year 2015. Only 1.2% of the articles in ACPLCs belong to classes with a total number of articles less than 500. As in the previous study, the distribution follows a typical scientometric distribution, and we therefore consider the results, regarding class sizes, as satisfying.

In the present study, we have not implemented a reclassification of small classes. However, in accordance with the previous study, we consider reclassification of small classes to be desirable for practical reasons. Moreover, we think that content labeling of classes is a topic for future work.

Another criterion stated by Šubelj et al. (2016) is that classes should make intuitive sense. In addition, we stress that the focus of a specialty should be possible to identify and that two specialties should have subject foci that can be distinguished. Two case studies, in which we have identified specialties within the disciplines of LIS and MI, have been performed to evaluate these criteria. We could identify the subject foci of the specialties in these case studies, and the subject foci of the specialties have been relatively easy to distinguish. Thus, the two criteria are (approximately) satisfied in our case. Further, several of the specialties identified in the LIS case have been identified by others (Bauer et al., 2016; Blessinger & Frasier, n.d.; Figuerola et al., 2017; Janssens et al., 2006) and the same holds for several of the specialties identified in the MI case (Kim & Delen, 2018; Schuemie et al., 2009; Wang et al., 2017). However, more case studies are needed to verify the soundness of the methodology used.

The aforementioned feature of the classification approach used in this study, logical classification, which assigns each topic to exactly one speciality, has some limitations. It is clear that topics can be addressed by several specialties (or at higher level disciplines). For instance,  Appendix 1 and 2 show that the topic with the label “NATURAL LANGUAGE PROCESSING//MEDICAL LANGUAGE PROCESSING//CLINICAL TEXT” is addressed by both the LIS and MI disciplines. This topic is forced into exactly one specialty, “ELECTRONIC HEALTH RECORDS//ELECTRONIC MEDICAL RECORD//MEDICAL INFORMATICS.” Thus, relations between this topic and, for example, specialties within the LIS discipline are not expressed by ACPLCs. However, relations between a specialty and topics within other specialties can still be analyzed using, for instance, citation relations. Nevertheless, a logical classification to some extent oversimplifies the complex structure of topic representation in research publications.

We acknowledge that direct citations perform less well than bibliographic coupling in a recent study (Waltman et al., 2019). However, a relatively low number of articles was used in the study, about 700,000 in comparison with the over 31 million articles used in this study. Moreover, a relatively short publication window (2007–2016), in comparison with the present study (1980–2016), was used. Interestingly, the study shows that an extended direct citation approach, in which direct citation relations within an extended set of publications are taken into account, performs better than an ordinary direct citation approach. Which publication-publication similarity measure to be used for the creation of an ACPLC still needs to be further investigated, however.

We recognize that there is only a small difference in performance, regarding the ARI values, between ACPLC_4P′, ACPLC_5P′ and ACPLC_6P′.7 Therefore, we can only determine the granularity of specialties roughly. This is, however, not surprising, given the complex, overlapping nature of research subject areas. Nevertheless, this study sets a benchmark of the size of specialties and outlines a methodology for the calibration of ACPLCs.

The combined outcome of our previous study on the classification of topics, and the present study on the classification of specialties, is a two-level hierarchical classification. We believe that such a classification comprises a valuable part of a research information system and propose that such a classification can be used for bibliometric analyses of topics and specialties.

Peter Sjögårde: Conceptualization; methodology; software; formal analysis; writing—original draft; writing—review & editing; visualization. Per Ahlgren: Conceptualization; methodology; formal analysis; writing—original draft; writing—review & editing.

The authors have no competing interests.

The data analyzed in this manuscript is subject to copyright (by Clarivate Analytics®, Philadelphia, Pennsylvania, USA) and cannot be made available.

We would like to thank two anonymous reviewers for their relevant and constructive comments on an earlier version of this paper.

2

A logical classification of a set of objects, O, is a set C of nonempty subsets of O such that (a) the union of the sets in C is equal to O, and (b) the sets in C are pairwise disjoint. Thus, each object in O is classified into exactly one set in C.

3
The self-citation ratio (s) for a journal j is given by:
$sj=csra$
(1)
where cs is the number of self-citations in j, and ra the total number of active references in j. References are considered as active if they point to publications covered by the data source (Waltman et al., 2013). A reference is considered as a self-citation if the referencing publication and the referenced publication belong to the same journal.
4
The overlap (y) between two journals (j1 and j2) is given by:
$y=12mA1+mA2$
(2)
where m is the number of shared cited references (i.e., cited references occurring in both j1 and j2), A1 the number of cited references in j1, and A2 the number of cited references in j2. The reference list of a journal was obtained by concatenating the reference lists of the articles (published year 2010) in the journal. If a reference article has been cited by more than one article in a journal, then this reference is counted multiple times for that journal. For example, if journal j1 has four references to article a and journal j2 has two references to article a, then journals j1 and j2 have two shared cited references with respect to article a. Note that we give the overlap measure threshold as a percentage in the running text.
5

Our approach differs slightly from the approach used by Waltman and van Eck (2012). The latter approach only uses average normalized direct citation values to reassign publications (at a given hierarchical level of the classification) that belong to clusters with an insufficient number of publications. Thus, the preliminary assignment of publications to clusters, which precedes the reassignment in question, is executed without the use of average normalized direct citation values. The reason for our deviation from the Waltman–van Eck approach is that Modularity Optimizer does not directly support their approach.

6

http://sankeymatic.com/ has been used for the illustration.

7

ACPLC_4P′ had the highest ARI value in an earlier version of the manuscript. In that version, BCPs was delimited to publications from 2010.

Ahlgren
,
P.
, &
Colliander
,
C.
(
2009
).
Document–document similarity approaches and science mapping: Experimental comparison of five approaches
.
Journal of Informetrics
,
3
(
1
),
49
63
. https://doi.org/10.1016/j.joi.2008.11.003
Bauer
,
J.
,
Leydesdorff
,
L.
, &
Bornmann
,
L.
(
2016
).
Highly cited papers in Library and Information Science (LIS): Authors, institutions, and network structures
.
Journal of the Association for Information Science and Technology
,
67
(
12
),
3095
3100
. https://doi.org/10.1002/asi.23568
Besselaar
,
P. van den
, &
Heimeriks
,
G.
(
2006
).
Mapping research topics using word-reference co-occurrences: A method and an exploratory case study
.
Scientometrics
,
68
(
3
),
377
393
. https://doi.org/10.1007/s11192-006-0118-9
Blessinger
,
K.
, &
Frasier
,
M.
(
n.d.
).
Analysis of a Decade in Library Literature: 1994–2004 | Blessinger | College & Research Libraries
. https://doi.org/10.5860/crl.68.2.155
Boyack
,
K. W.
(
2017
).
Investigating the effect of global data on topic detection
.
Scientometrics
,
111
(
2
),
999
1015
. https://doi.org/10.1007/s11192-017-2297-y
Boyack
,
K. W.
,
Klavans
,
R.
,
Small
,
H.
, &
Ungar
,
L.
(
2014
).
Characterizing the emergence of two nanotechnology topics using a contemporaneous global micro-model of science
.
Journal of Engineering and Technology Management
,
32
,
147
159
. https://doi.org/10.1016/j.jengtecman.2013.07.001
Boyack
,
K. W.
,
Newman
,
D.
,
Duhon
,
R. J.
,
Klavans
,
R.
,
Patek
,
M.
,
Biberstine
,
J. R.
et al
(
2011
).
Clustering More than Two Million Biomedical Publications: Comparing the Accuracies of Nine Text-Based Similarity Approaches
.
PLoS ONE
,
6
(
3
),
e18029
.https://doi.org/10.1371/journal.pone.0018029
,
S. C.
(
1948
).
Documentation
.
London
:
Lockwood
.
Chubin
,
D. E.
(
1976
).
State of the field: The conceptualization of scientific specialties
.
Sociological Quarterly
,
17
(
4
),
448
476
. https://doi.org/10.1111/j.1533-8525.1976.tb01715.x
Colliander
,
C.
(
2015
).
A novel approach to citation normalization: A similarity-based method for creating reference sets
.
Journal of the Association for Information Science and Technology
,
66
(
3
),
489
500
. https://doi.org/10.1002/asi.23193
Colliander
,
Cristian
. (
2014
).
Science mapping and research evaluation: A novel methodology for creating normalized citation indicators and estimating their stability
(
Doctoral thesis
).
Crane
,
D.
(
1972
).
Invisible Colleges: Diffusion of Knowledge in Scientific Communities
.
Chicago
:
University Of Chicago Press
.
Figuerola
,
C. G.
,
García Marco
,
F. J.
, &
Pinto
,
M.
(
2017
).
Mapping the evolution of library and information science (1978–2014) using topic modeling on LISA
.
Scientometrics
,
112
(
3
),
1507
1535
. https://doi.org/10.1007/s11192-017-2432-9
Fortunato
,
S.
(
2010
).
Community detection in graphs
.
Physics Reports
,
486
(
3–5
),
75
174
. https://doi.org/10.1016/j.physrep.2009.11.002
Glänzel
,
W.
, &
Thijs
,
B.
(
2017
).
Using hybrid methods and “core documents” for the representation of clusters and topics: The astronomy dataset
.
Scientometrics
,
111
(
2
),
1071
1087
. https://doi.org/10.1007/s11192-017-2301-6
Hagstrom
,
W.
(
1970
).
Factors related to the use of different modes of publishing research in four scientific fields
. In
E. C.
Nelson
&
K. D.
Pollock
(Eds.),
Communication Among Scientists and Engineers
(pp.
85
124
).
Lexington, MA
:
Heath Lexington Books
.
Hubert
,
L.
, &
Arabie
,
P.
(
1985
).
Comparing partitions
.
Journal of Classification
,
2
(
1
),
193
218
. https://doi.org/10.1007/BF01908075
Janssens
,
F.
,
Leta
,
J.
,
Glänzel
,
W.
, &
De Moor
,
B.
(
2006
).
Towards mapping library and information science
.
Information Processing & Management
,
42
(
6
),
1614
1642
. https://doi.org/10.1016/j.ipm.2006.03.025
Kessler
,
M. M.
(
1965
).
Comparison of the results of bibliographic coupling and analytic subject indexing
.
American Documentation
,
16
(
3
),
223
233
. https://doi.org/10.1002/asi.5090160309
Kim
,
Y.-M.
, &
Delen
,
D.
(
2018
).
Medical informatics research trend analysis: A text mining approach
.
Health Informatics Journal
,
24
(
4
),
432
452
. https://doi.org/10.1177/1460458216678443
Klavans
,
R.
, &
Boyack
,
K. W.
(
2017a
).
Research portfolio analysis and topic prominence
.
Journal of Informetrics
,
11
(
4
),
1158
1174
. https://doi.org/10.1016/j.joi.2017.10.002
Klavans
,
R.
, &
Boyack
,
K. W.
(
2017b
).
Which Type of Citation Analysis Generates the Most Accurate Taxonomy of Scientific and Technical Knowledge?
Journal of the Association for Information Science and Technology
,
68
(
4
),
984
998
. https://doi.org/10.1002/asi.23734
Kuhn
,
T. S.
(
1996
).
The Structure of Scientific Revolutions
(3rd edition).
Chicago, IL
:
University of Chicago Press
.
Lotka
,
A.
(
1926
).
The frequency distribution of scientific productivity
.
Journal of the Washington Academy of Science
,
16
,
317
323
.
Lucio-Arias
,
D.
, &
Leydesdorff
,
L.
(
2009
).
An indicator of research front activity: Measuring intellectual organization as uncertainty reduction in document sets
.
Journal of the American Society for Information Science and Technology
,
60
(
12
),
2488
2498
. https://doi.org/10.1002/asi.21199
Marshakova-Shaikevich
,
I.
(
1973
).
System of document connections based on references
.
Nauchno-Tekhnicheskaya Informatsiya Seriya 2-Informatsionnye Protsessy
, (
6
),
3
8
.
Morris
,
S. A.
(
2005
).
Manifestation of emerging specialties in journal literature: A growth model of papers, references, exemplars, bibliographic coupling, cocitation, and clustering coefficient distribution
.
Journal of the American Society for Information Science and Technology
,
56
(
12
),
1250
1273
. https://doi.org/10.1002/asi.20208
Morris
,
S. A.
, &
Van der Veer Martens
,
B.
(
2008
).
Mapping research specialties
.
Annual Review of Information Science and Technology
,
42
(
1
),
213
295
. https://doi.org/10.1002/aris.2008.1440420113
Price
,
D. J. de S.
(
1965
).
Little Science, Big Science
.
New York
:
Columbia University Press
.
Rand
,
W. M.
(
1971
).
Objective Criteria for the Evaluation of Clustering Methods
.
Journal of the American Statistical Association
,
66
(
336
),
846
850
. https://doi.org/10.2307/2284239
Scharnhorst
,
A.
,
Börner
,
K.
, &
Besselaar
,
P.
(
2012
).
Models of Science Dynamics
.
Springer
:
Berlin, Heidelberg
.
Schuemie
,
M. J.
,
Talmon
,
J. L.
,
Moorman
,
P. W.
, &
Kors
,
J. A.
(
2009
).
Mapping the domain of medical informatics
.
Methods of Information in Medicine
,
48
(
1
),
76
83
.
Sjögårde
,
P.
, &
Ahlgren
,
P.
(
2018
).
Granularity of algorithmically constructed publication-level classifications of research publications: Identification of topics
.
Journal of Informetrics
,
12
(
1
),
133
152
. https://doi.org/10.1016/j.joi.2017.12.006
Small
,
H.
(
1973
).
Co-citation in the scientific literature: A new measure of the relationship between two documents
.
Journal of the American Society for Information Science
,
24
(
4
),
265
269
. https://doi.org/10.1002/asi.4630240406
Small
,
H.
, &
Griffith
,
B. C.
(
1974
).
The structure of scientific literatures I: Identifying and graphing specialties
.
Science Studies
,
4
(
1
),
17
40
.
Šubelj
,
L.
,
van Eck
,
N. J.
, &
Waltman
,
L.
(
2016
).
Clustering scientific publications based on citation relations: A systematic comparison of different methods
.
PLoS ONE
,
11
(
4
),
e0154404
. https://doi.org/10.1371/journal.pone.0154404
Traag
,
V. A.
,
Waltman
,
L.
, &
Eck
,
N. J. van
. (
2019
).
From Louvain to Leiden: Guaranteeing well-connected communities
.
Scientific Reports
,
9
(
1
),
5233
. https://doi.org/10.1038/s41598-019-41695-z
Traag
,
V.
,
Dooren
,
P.
, &
van Nesterov
,
Y.
(
2011
).
Narrow scope for resolution-limit-free community detection
.
Physical Review E
,
84
(
1
),
016114
. https://doi.org/10.1103/PhysRevE.84.016114
Waltman
,
L.
, &
van Eck
,
N. J.
(
2012
).
A new methodology for constructing a publication-level classification system of science
.
Journal of the American Society for Information Science and Technology
,
63
(
12
),
2378
2392
. https://doi.org/10.1002/asi.22748
Waltman
,
L.
, &
van Eck
,
N. J.
(
2013
).
A smart local moving algorithm for large-scale modularity-based community detection
.
The European Physical Journal B
,
86
(
11
),
471
. https://doi.org/10.1140/epjb/e2013-40829-0
Waltman
,
L.
,
van Eck
,
N. J.
,
van Leeuwen
,
T. N.
, &
Visser
,
M. S.
(
2013
).
Some modifications to the SNIP journal impact indicator
.
Journal of Informetrics
,
7
(
2
),
272
285
. https://doi.org/10.1016/j.joi.2012.11.011
Waltman
,
L.
,
Boyack
,
K. W.
,
Colavizza
,
G.
, &
van Eck
,
N. J.
(
2019
).
A Principled Methodology for Comparing Relatedness Measures for Clustering Publications
ArXiv:1901.06815 [Cs], http://arxiv.org/abs/1901.06815.
Wang
,
L.
,
Topaz
,
M.
,
Plasek
,
J. M.
, &
Zhou
,
L.
(
2017
).
Content and trends in medical informatics publications over the past two decades
.
Studies in Health Technology and Informatics
,
245
,
968
972
.
Wen
,
B.
,
Horlings
,
E.
,
van der Zouwen
,
M.
, &
van den Besselaar
,
P.
(
2017
).
Mapping science through bibliometric triangulation: An experimental approach applied to water research
.
Journal of the Association for Information Science and Technology
,
68
(
3
),
724
738
. https://doi.org/10.1002/asi.23696
Yan
,
E.
,
Ding
,
Y.
, &
Jacob
,
E. K.
(
2012
).
Overlaying communities and topics: An analysis on publication networks
.
Scientometrics
,
90
(
2
),
499
513
. https://doi.org/10.1007/s11192-011-0531-6

### APPENDIX

Appendix 1.
Topics per Specialty – LIS
SPECIALTY# articles in Plis# articles in topicShare of topic in Plis
TOPIC
BIBLIOMETRICS//CITATION ANALYSIS//IMPACT FACTOR
FIELD NORMALIZATION//SOURCE NORMALIZATION//RESEARCH EVALUATION 193 258 75%
H INDEX//HIRSCH INDEX//G INDEX 190 317 60%
RESEARCH COLLABORATION//SCIENTIFIC COLLABORATION//CO AUTHORSHIP 125 184 68%
AUTHOR CO CITATION ANALYSIS//BIBLIOGRAPHIC COUPLING//CO CITATION ANALYSIS 83 142 58%
GOOGLE SCHOLAR//SCOPUS//WEB OF SCIENCE 79 121 65%
ALTMETRICS//MENDELEY//RESEARCHGATE 75 113 66%
OVERLAY MAP//SCIENCE OVERLAY MAPS//JOURNAL CLASSIFICATION 75 148 51%
CO AUTHORSHIP NETWORKS//SCIENTIFIC COLLABORATION//CO AUTHOR NETWORKS 70 136 51%
BOOK CITATION INDEX//SOCIAL SCIENCES AND HUMANITIES//BOOK PUBLISHERS 65 93 70%
WEBOMETRICS//WEB VISIBILITY//WEB LINKS 60 80 75%

INFORMATION LITERACY//INFORMATION LITERACY INSTRUCTION//LIBRARY INSTRUCTION 194 212 92%
LIBRARY 20//LIBRARIAN 2//ACADEMIC LIBRARIES 104 110 95%
KNOWLEDGE ORGANIZATION//FACETED CLASSIFICATIONS//INDEXING LANGUAGE 93 106 88%
INTERACTIVE INFORMATION RETRIEVAL//END USER SEARCHING//INFORMATION NEEDS AND USES 92 128 72%
INFORMATION PRACTICES//AIDS TALK//BARRIERS TO INFORMATION SEEKING 85 99 86%
INFORMATION SCIENCE//DIKW HIERARCHY//PROPERTIES OF DOCUMENTARY PRACTICE 81 99 82%
PUBLIC LIBRARIES//CHILDRENS INTERNET PROTECTION ACT//RURAL LIBRARIES 62 68 91%
REFERENCE SERVICES//DIGITAL REFERENCE//REFERENCE DESK 61 66 92%
HOPE OLSON//BISAC//KNOWLEDGE ORGANIZATION 57 66 86%

ELECTRONIC BOOKS//E BOOKS//E TEXTBOOK 134 172 78%
OPEN ACCESS//OPEN ACCESS JOURNALS//GOLD OPEN ACCESS 123 218 56%
DOCUMENT DELIVERY//INTERLENDING//INTERLIBRARY LOAN 121 122 99%
ELECTRONIC JOURNALS//ELECTRONIC PERIODICALS//E JOURNALS 79 85 93%
KOHA//INTEGRATED LIBRARY SYSTEMS//WEB SCALE DISCOVERY 72 78 92%
INSTITUTIONAL REPOSITORIES//ACADEMIC AUTHORS//DIGITAL LIBRARY FRAMEWORK 63 69 91%
RESEARCH DATA//DATA SHARING//DATA REPOSITORIES 53 147 36%
INTERFACE CONSISTENCY//ADAPTIVE LIBRARY SERVICES//ALEXANDRIA DIGITAL LIBRARY PROJECT 36 46 78%
CITATION STUDY//COLLECTION ASSESSMENT//ACADEMIC MEDICAL CENTER LIBRARY 31 38 82%
FRBR//DESCRIPTIVE CATALOGUING//FUNCTIONAL REQUIREMENTS FOR BIBLIOGRAPHIC RECORDS FRBR 29 35 83%

RECOMMENDER SYSTEMS//COLLABORATIVE FILTERING//INFORMATION RETRIEVAL
FOLKSONOMY//SOCIAL TAGGING//COLLABORATIVE TAGGING 57 159 36%
SENTIMENT ANALYSIS//OPINION MINING//SENTIMENT CLASSIFICATION 35 371 9%
RECOMMENDER SYSTEMS//COLLABORATIVE FILTERING//RECOMMENDATION SYSTEM 30 576 5%
RELEVANCE CRITERIA//RELEVANCE JUDGEMENT//TEST COLLECTIONS 25 49 51%
SESSION IDENTIFICATION//QUERY LOG ANALYSIS//QUERY RECOMMENDATION 24 86 28%
COLLABORATIVE INFORMATION SEEKING//SEARCH HISTORIES//SOCIAL SEARCH 22 40 55%
EXPERT FINDING//EXPERT SEARCH//ENTITY RETRIEVAL 20 87 23%
MULTI DOCUMENT SUMMARIZATION//TEXT SUMMARIZATION//DOCUMENT SUMMARIZATION 16 146 11%
STEMMING//CROSS LANGUAGE INFORMATION RETRIEVAL//CHARACTER N GRAMS 11 40 28%

ELECTRONIC HEALTH RECORDS//ELECTRONIC MEDICAL RECORD//MEDICAL INFORMATICS
NATURAL LANGUAGE PROCESSING//MEDICAL LANGUAGE PROCESSING//CLINICAL TEXT 92 278 33%
HEALTH INFORMATION TECHNOLOGY//ELECTRONIC HEALTH RECORDS//MEANINGFUL USE 46 392 12%
ALERT FATIGUE//CLINICAL DECISION SUPPORT SYSTEMS//CLINICAL DECISION SUPPORT 43 216 20%
CDISC//ISO IEC 11179//CLINICAL RESEARCH INFORMATICS 37 167 22%
PHEWAS//PHENOME WIDE ASSOCIATION STUDY//CLINICAL PHENOTYPE MODELING 34 160 21%
HEALTH INFORMATION EXCHANGE//HEALTH RECORD BANK//REGIONAL HEALTH INFORMATION ORGANIZATIONS 32 154 21%
CPOE//E PRESCRIBING//ELECTRONIC PRESCRIBING 31 218 14%
OPENEHR//LOINC//CLINICAL ARCHETYPES 21 111 19%
SNOMED CT//UMLS//ABSTRACTION NETWORK 13 108 12%
COPY PASTE//CLINICAL DOCUMENTATION//COMPUTER BASED DOCUMENTATION 10 59 17%

ENTERPRISE RESOURCE PLANNING//ENTERPRISE RESOURCE PLANNING ERP//END USER COMPUTING
STRATEGIC INFORMATION SYSTEMS PLANNING//CHIEF INFORMATION OFFICER//IT GOVERNANCE 70 124 56%
IS RESEARCH//REFERENCE DISCIPLINE//IS DISCIPLINE 65 83 78%
ENTERPRISE RESOURCE PLANNING//ENTERPRISE RESOURCE PLANNING ERP//ERP IMPLEMENTATION 41 196 21%
TOE FRAMEWORK//E COMMERCE ADOPTION//TECHNOLOGY ORGANIZATION ENVIRONMENT FRAMEWORK 38 136 28%
REQUIREMENTS UNCERTAINTY//SYSTEM SUCCESS//SOFTWARE PROJECT RISK 23 81 28%
CAREER ANCHORS//IS PERSONNEL//IT WORKFORCE 23 49 47%
DATA QUALITY//INFORMATION QUALITY MANAGEMENT//INFORMATION QUALITY 15 68 22%
USER SATISFACTION//INFORMATION SYSTEMS SUCCESS//IS SUCCESS 15 81 19%
SUBJECTIVITY STUDY//ACTOR ENGAGEMENT//AGILE ANALYTICS 12 73 16%

KNOWLEDGE MANAGEMENT//KNOWLEDGE SHARING//OPEN SOURCE SOFTWARE
KNOWLEDGE SHARING//KNOWLEDGE MANAGEMENT//KNOWLEDGE SHARING BEHAVIOR 151 328 46%
KNOWLEDGE MANAGEMENT//ENTERPRISE BENEFITS//KNOWLEDGE CHAIN 58 101 57%
OPEN SOURCE SOFTWARE//OPEN SOURCE//OPEN SOURCE SOFTWARE OSS 53 230 23%
WIKIPEDIA//COOPERATIVE KNOWLEDGE GENERATION//ENCYCLOPAEDIAS 22 76 29%
PERSONAL INFORMATION MANAGEMENT//ADAPTIVE WINDOW MANAGER//ADVANCED MANAGEMENT OF PERSONAL INFORMATION 22 48 46%
COMMUNITIES OF PRACTICE//ORGANIZING PRACTICES//COMMUNITY OF PRACTICE 19 82 23%
INTELLECTUAL CAPITAL//INTANGIBLE ASSETS//INTELLECTUAL CAPITAL IC 19 96 20%
ENTERPRISE EVOLUTION//KNOWLEDGE CREATION//AUTOMOBILE PROJECT 16 43 37%
EUROPEAN SMES//BARRIERS OF IMPLEMENTATION//CASE STUDY IN SINGAPORE 13 35 37%
BLACK HAT SEO//COMMUNICATIONS ACTIVITIES//CONSUMER COMPARISON 11 28 39%

INNOVATION//PATENTS//OPEN INNOVATION
PATENT ANALYSIS//PATENT MINING//TECHNOLOGY INTELLIGENCE 41 179 23%
NON PATENT REFERENCES//NON PATENT CITATION//SCIENCE LINKAGE 34 57 60%
PROBABILISTIC ENTROPY//UNIVERSITY INDUSTRY GOVERNMENT RELATIONSHIP//TRIPLE HELIX 32 52 62%
ACADEMIC ENTREPRENEURSHIP//ENTREPRENEURIAL UNIVERSITY//UNIVERSITY SPIN OFFS 27 421 6%
PATENT VALUE//PATENTS//PATENT SYSTEM 27 202 13%
USER INNOVATION//LEAD USERS//INNOVATION CONTESTS 19 226 8%
SOFTWARE ECOSYSTEMS//BUSINESS ECOSYSTEM//MOBILE COMPUTING INDUSTRY 16 81 20%
ABSORPTIVE CAPACITY//POTENTIAL ABSORPTIVE CAPACITY//COMBINATIVE CAPABILITIES 13 102 13%
NATIONAL ELIGIBILITY TEST//RD EFFICIENCY//CHINAS HIGH TECH INNOVATIONS 10 47 21%
INVENTIVE ACTIVITIES//ASSIGNEE//CO PATENT 17 53%

UNIVERSAL SERVICE//TELECOMMUNICATIONS//ACCESS PRICING
ACCESS REGULATION//ACCESS PRICING//NEXT GENERATION ACCESS NETWORKS 48 121 40%
TD SCDMA//FORMAL STANDARDS//WAPI 39 63 62%
SPECTRUM AUCTIONS//DIGITAL DIVIDEND//SPECTRUM TRADING 28 68 41%
FIXED MOBILE SUBSTITUTION//MOBILE TELECOMMUNICATIONS//FIXED TO MOBILE SUBSTITUTION 24 56 43%
BILL AND KEEP//TERMINATION RATES//ACCESS PRICING 17 60 28%
UNIVERSAL SERVICE//E RATE//UNIVERSAL SERVICE FUND 17 35 49%
NET NEUTRALITY//NETWORK NEUTRALITY//CONTENT PROVIDERS 17 70 24%
PRICE CAPS//INCENTIVE REGULATION//PRICE CAP REGULATION 12 39 31%
AUSTRALIAN EXPERIENCE//BARRIERS TO TRADE AND INVESTMENT//CAUSAL CHAIN OF REFORM 30 27%

HEALTH LITERACY//INTERNET//MHEALTH
HEALTH LITERACY//NEWEST VITAL SIGN//S TOFHLA 73 544 13%
HEALTH INFORMATION SEEKING//HEALTH INFORMATION AVOIDANCE//INFORMATION SEEKING 35 118 30%
ONLINE SUPPORT GROUPS//COMPREHENSIVE HEALTH ENHANCEMENT SUPPORT SYSTEM CHESS//INTERNET CANCER SUPPORT GROUPS 28 220 13%
MHEALTH//MEDICATION REMINDERS//REAL TIME ADHERENCE MONITORING 20 275 7%
INTERNET//HEALTH INFORMATION//ONLINE HEALTH INFORMATION 14 193 7%
TEXT MESSAGING//TEXT MESSAGE//MHEALTH 13 218 6%
DISCERN//INTERNET//QUALITY OF INFORMATION 207 4%
INTERNET CHILD HEALTH INFORMATION//ASSESSMENT OF ACUTE DISEASES//AUTISM CEREBRAL PALSY 46 15%
SPECIALTY# articles in Plis# articles in topicShare of topic in Plis
TOPIC
BIBLIOMETRICS//CITATION ANALYSIS//IMPACT FACTOR
FIELD NORMALIZATION//SOURCE NORMALIZATION//RESEARCH EVALUATION 193 258 75%
H INDEX//HIRSCH INDEX//G INDEX 190 317 60%
RESEARCH COLLABORATION//SCIENTIFIC COLLABORATION//CO AUTHORSHIP 125 184 68%
AUTHOR CO CITATION ANALYSIS//BIBLIOGRAPHIC COUPLING//CO CITATION ANALYSIS 83 142 58%
GOOGLE SCHOLAR//SCOPUS//WEB OF SCIENCE 79 121 65%
ALTMETRICS//MENDELEY//RESEARCHGATE 75 113 66%
OVERLAY MAP//SCIENCE OVERLAY MAPS//JOURNAL CLASSIFICATION 75 148 51%
CO AUTHORSHIP NETWORKS//SCIENTIFIC COLLABORATION//CO AUTHOR NETWORKS 70 136 51%
BOOK CITATION INDEX//SOCIAL SCIENCES AND HUMANITIES//BOOK PUBLISHERS 65 93 70%
WEBOMETRICS//WEB VISIBILITY//WEB LINKS 60 80 75%

INFORMATION LITERACY//INFORMATION LITERACY INSTRUCTION//LIBRARY INSTRUCTION 194 212 92%
LIBRARY 20//LIBRARIAN 2//ACADEMIC LIBRARIES 104 110 95%
KNOWLEDGE ORGANIZATION//FACETED CLASSIFICATIONS//INDEXING LANGUAGE 93 106 88%
INTERACTIVE INFORMATION RETRIEVAL//END USER SEARCHING//INFORMATION NEEDS AND USES 92 128 72%
INFORMATION PRACTICES//AIDS TALK//BARRIERS TO INFORMATION SEEKING 85 99 86%
INFORMATION SCIENCE//DIKW HIERARCHY//PROPERTIES OF DOCUMENTARY PRACTICE 81 99 82%
PUBLIC LIBRARIES//CHILDRENS INTERNET PROTECTION ACT//RURAL LIBRARIES 62 68 91%
REFERENCE SERVICES//DIGITAL REFERENCE//REFERENCE DESK 61 66 92%
HOPE OLSON//BISAC//KNOWLEDGE ORGANIZATION 57 66 86%

ELECTRONIC BOOKS//E BOOKS//E TEXTBOOK 134 172 78%
OPEN ACCESS//OPEN ACCESS JOURNALS//GOLD OPEN ACCESS 123 218 56%
DOCUMENT DELIVERY//INTERLENDING//INTERLIBRARY LOAN 121 122 99%
ELECTRONIC JOURNALS//ELECTRONIC PERIODICALS//E JOURNALS 79 85 93%
KOHA//INTEGRATED LIBRARY SYSTEMS//WEB SCALE DISCOVERY 72 78 92%
INSTITUTIONAL REPOSITORIES//ACADEMIC AUTHORS//DIGITAL LIBRARY FRAMEWORK 63 69 91%
RESEARCH DATA//DATA SHARING//DATA REPOSITORIES 53 147 36%
INTERFACE CONSISTENCY//ADAPTIVE LIBRARY SERVICES//ALEXANDRIA DIGITAL LIBRARY PROJECT 36 46 78%
CITATION STUDY//COLLECTION ASSESSMENT//ACADEMIC MEDICAL CENTER LIBRARY 31 38 82%
FRBR//DESCRIPTIVE CATALOGUING//FUNCTIONAL REQUIREMENTS FOR BIBLIOGRAPHIC RECORDS FRBR 29 35 83%

RECOMMENDER SYSTEMS//COLLABORATIVE FILTERING//INFORMATION RETRIEVAL
FOLKSONOMY//SOCIAL TAGGING//COLLABORATIVE TAGGING 57 159 36%
SENTIMENT ANALYSIS//OPINION MINING//SENTIMENT CLASSIFICATION 35 371 9%
RECOMMENDER SYSTEMS//COLLABORATIVE FILTERING//RECOMMENDATION SYSTEM 30 576 5%
RELEVANCE CRITERIA//RELEVANCE JUDGEMENT//TEST COLLECTIONS 25 49 51%
SESSION IDENTIFICATION//QUERY LOG ANALYSIS//QUERY RECOMMENDATION 24 86 28%
COLLABORATIVE INFORMATION SEEKING//SEARCH HISTORIES//SOCIAL SEARCH 22 40 55%
EXPERT FINDING//EXPERT SEARCH//ENTITY RETRIEVAL 20 87 23%
MULTI DOCUMENT SUMMARIZATION//TEXT SUMMARIZATION//DOCUMENT SUMMARIZATION 16 146 11%
STEMMING//CROSS LANGUAGE INFORMATION RETRIEVAL//CHARACTER N GRAMS 11 40 28%

ELECTRONIC HEALTH RECORDS//ELECTRONIC MEDICAL RECORD//MEDICAL INFORMATICS
NATURAL LANGUAGE PROCESSING//MEDICAL LANGUAGE PROCESSING//CLINICAL TEXT 92 278 33%
HEALTH INFORMATION TECHNOLOGY//ELECTRONIC HEALTH RECORDS//MEANINGFUL USE 46 392 12%
ALERT FATIGUE//CLINICAL DECISION SUPPORT SYSTEMS//CLINICAL DECISION SUPPORT 43 216 20%
CDISC//ISO IEC 11179//CLINICAL RESEARCH INFORMATICS 37 167 22%
PHEWAS//PHENOME WIDE ASSOCIATION STUDY//CLINICAL PHENOTYPE MODELING 34 160 21%
HEALTH INFORMATION EXCHANGE//HEALTH RECORD BANK//REGIONAL HEALTH INFORMATION ORGANIZATIONS 32 154 21%
CPOE//E PRESCRIBING//ELECTRONIC PRESCRIBING 31 218 14%
OPENEHR//LOINC//CLINICAL ARCHETYPES 21 111 19%
SNOMED CT//UMLS//ABSTRACTION NETWORK 13 108 12%
COPY PASTE//CLINICAL DOCUMENTATION//COMPUTER BASED DOCUMENTATION 10 59 17%

ENTERPRISE RESOURCE PLANNING//ENTERPRISE RESOURCE PLANNING ERP//END USER COMPUTING
STRATEGIC INFORMATION SYSTEMS PLANNING//CHIEF INFORMATION OFFICER//IT GOVERNANCE 70 124 56%
IS RESEARCH//REFERENCE DISCIPLINE//IS DISCIPLINE 65 83 78%
ENTERPRISE RESOURCE PLANNING//ENTERPRISE RESOURCE PLANNING ERP//ERP IMPLEMENTATION 41 196 21%
TOE FRAMEWORK//E COMMERCE ADOPTION//TECHNOLOGY ORGANIZATION ENVIRONMENT FRAMEWORK 38 136 28%
REQUIREMENTS UNCERTAINTY//SYSTEM SUCCESS//SOFTWARE PROJECT RISK 23 81 28%
CAREER ANCHORS//IS PERSONNEL//IT WORKFORCE 23 49 47%
DATA QUALITY//INFORMATION QUALITY MANAGEMENT//INFORMATION QUALITY 15 68 22%
USER SATISFACTION//INFORMATION SYSTEMS SUCCESS//IS SUCCESS 15 81 19%
SUBJECTIVITY STUDY//ACTOR ENGAGEMENT//AGILE ANALYTICS 12 73 16%

KNOWLEDGE MANAGEMENT//KNOWLEDGE SHARING//OPEN SOURCE SOFTWARE
KNOWLEDGE SHARING//KNOWLEDGE MANAGEMENT//KNOWLEDGE SHARING BEHAVIOR 151 328 46%
KNOWLEDGE MANAGEMENT//ENTERPRISE BENEFITS//KNOWLEDGE CHAIN 58 101 57%
OPEN SOURCE SOFTWARE//OPEN SOURCE//OPEN SOURCE SOFTWARE OSS 53 230 23%
WIKIPEDIA//COOPERATIVE KNOWLEDGE GENERATION//ENCYCLOPAEDIAS 22 76 29%
PERSONAL INFORMATION MANAGEMENT//ADAPTIVE WINDOW MANAGER//ADVANCED MANAGEMENT OF PERSONAL INFORMATION 22 48 46%
COMMUNITIES OF PRACTICE//ORGANIZING PRACTICES//COMMUNITY OF PRACTICE 19 82 23%
INTELLECTUAL CAPITAL//INTANGIBLE ASSETS//INTELLECTUAL CAPITAL IC 19 96 20%
ENTERPRISE EVOLUTION//KNOWLEDGE CREATION//AUTOMOBILE PROJECT 16 43 37%
EUROPEAN SMES//BARRIERS OF IMPLEMENTATION//CASE STUDY IN SINGAPORE 13 35 37%
BLACK HAT SEO//COMMUNICATIONS ACTIVITIES//CONSUMER COMPARISON 11 28 39%

INNOVATION//PATENTS//OPEN INNOVATION
PATENT ANALYSIS//PATENT MINING//TECHNOLOGY INTELLIGENCE 41 179 23%
NON PATENT REFERENCES//NON PATENT CITATION//SCIENCE LINKAGE 34 57 60%
PROBABILISTIC ENTROPY//UNIVERSITY INDUSTRY GOVERNMENT RELATIONSHIP//TRIPLE HELIX 32 52 62%
ACADEMIC ENTREPRENEURSHIP//ENTREPRENEURIAL UNIVERSITY//UNIVERSITY SPIN OFFS 27 421 6%
PATENT VALUE//PATENTS//PATENT SYSTEM 27 202 13%
USER INNOVATION//LEAD USERS//INNOVATION CONTESTS 19 226 8%
SOFTWARE ECOSYSTEMS//BUSINESS ECOSYSTEM//MOBILE COMPUTING INDUSTRY 16 81 20%
ABSORPTIVE CAPACITY//POTENTIAL ABSORPTIVE CAPACITY//COMBINATIVE CAPABILITIES 13 102 13%
NATIONAL ELIGIBILITY TEST//RD EFFICIENCY//CHINAS HIGH TECH INNOVATIONS 10 47 21%
INVENTIVE ACTIVITIES//ASSIGNEE//CO PATENT 17 53%

UNIVERSAL SERVICE//TELECOMMUNICATIONS//ACCESS PRICING
ACCESS REGULATION//ACCESS PRICING//NEXT GENERATION ACCESS NETWORKS 48 121 40%
TD SCDMA//FORMAL STANDARDS//WAPI 39 63 62%
SPECTRUM AUCTIONS//DIGITAL DIVIDEND//SPECTRUM TRADING 28 68 41%
FIXED MOBILE SUBSTITUTION//MOBILE TELECOMMUNICATIONS//FIXED TO MOBILE SUBSTITUTION 24 56 43%
BILL AND KEEP//TERMINATION RATES//ACCESS PRICING 17 60 28%
UNIVERSAL SERVICE//E RATE//UNIVERSAL SERVICE FUND 17 35 49%
NET NEUTRALITY//NETWORK NEUTRALITY//CONTENT PROVIDERS 17 70 24%
PRICE CAPS//INCENTIVE REGULATION//PRICE CAP REGULATION 12 39 31%
AUSTRALIAN EXPERIENCE//BARRIERS TO TRADE AND INVESTMENT//CAUSAL CHAIN OF REFORM 30 27%

HEALTH LITERACY//INTERNET//MHEALTH
HEALTH LITERACY//NEWEST VITAL SIGN//S TOFHLA 73 544 13%
HEALTH INFORMATION SEEKING//HEALTH INFORMATION AVOIDANCE//INFORMATION SEEKING 35 118 30%
ONLINE SUPPORT GROUPS//COMPREHENSIVE HEALTH ENHANCEMENT SUPPORT SYSTEM CHESS//INTERNET CANCER SUPPORT GROUPS 28 220 13%
MHEALTH//MEDICATION REMINDERS//REAL TIME ADHERENCE MONITORING 20 275 7%
INTERNET//HEALTH INFORMATION//ONLINE HEALTH INFORMATION 14 193 7%
TEXT MESSAGING//TEXT MESSAGE//MHEALTH 13 218 6%
DISCERN//INTERNET//QUALITY OF INFORMATION 207 4%
INTERNET CHILD HEALTH INFORMATION//ASSESSMENT OF ACUTE DISEASES//AUTISM CEREBRAL PALSY 46 15%

Appendix 2.
Topics per Specialty – MIS
SPECIALTY# articles in Pmi# articles in topicShare of topic in Pmi
TOPIC
ELECTRONIC HEALTH RECORDS//ELECTRONIC MEDICAL RECORD//MEDICAL INFORMATICS
NATURAL LANGUAGE PROCESSING//MEDICAL LANGUAGE PROCESSING//CLINICAL TEXT 188 278 68%
HEALTH INFORMATION TECHNOLOGY//ELECTRONIC HEALTH RECORDS//MEANINGFUL USE 127 392 32%
CDISC//ISO IEC 11179//CLINICAL RESEARCH INFORMATICS 112 167 67%
ALERT FATIGUE//CLINICAL DECISION SUPPORT SYSTEMS//CLINICAL DECISION SUPPORT 110 216 51%
NURSING INFORMATION SYSTEM//CLINICAL INFORMATION SYSTEMS//DOCUMENTATION TIME 104 152 68%
OPENEHR//LOINC//CLINICAL ARCHETYPES 89 111 80%
HEALTH INFORMATION EXCHANGE//HEALTH RECORD BANK//REGIONAL HEALTH INFORMATION ORGANIZATIONS 87 154 56%
CPOE//E PRESCRIBING//ELECTRONIC PRESCRIBING 84 218 39%
SNOMED CT//UMLS//ABSTRACTION NETWORK 76 108 70%
PHEWAS//PHENOME WIDE ASSOCIATION STUDY//CLINICAL PHENOTYPE MODELING 49 160 31%

HEALTH LITERACY//INTERNET//MHEALTH
INTERNET//HEALTH INFORMATION//ONLINE HEALTH INFORMATION 48 193 25%
ONLINE SUPPORT GROUPS//COMPREHENSIVE HEALTH ENHANCEMENT SUPPORT SYSTEM CHESS//INTERNET CANCER SUPPORT GROUPS 37 220 17%
MEDICAL APP//APPS//SMARTPHONE 33 165 20%
MHEALTH//MEDICATION REMINDERS//REAL TIME ADHERENCE MONITORING 32 275 12%
E PROFESSIONALISM//SOCIAL MEDIA//TWITTER MESSAGING 30 274 11%
TEXT MESSAGING//TEXT MESSAGE//MHEALTH 29 218 13%
MOBILE APPS//APPS//MHEALTH 25 126 20%
PHYSICIAN RATING WEBSITE//RATING SITES//QUALITY TRANSPARENCY 23 61 38%

HEALTH TECHNOLOGY ASSESSMENT//EQ 5D//PRIORITY SETTING
HEALTH TECHNOLOGY ASSESSMENT//HOSPITAL BASED HTA//MINI HTA 58 118 49%
EQ 5D//SF 6D//EQ 5D 5L 38 411 9%
VALUE OF INFORMATION//OPTIMAL TRIAL DESIGN//VALUE OF INFORMATION ANALYSIS 29 95 31%
HEALTH TECHNOLOGY ASSESSMENT//INSTITUTE FOR QUALITY AND EFFICIENCY IN HEALTH CARE//FOURTH HURDLE 28 153 18%
DYNAMIC TRANSMISSION//HALF CYCLE CORRECTION//COST EFFECTIVENESS MODELING 26 82 32%
STRENGTH OF PREFERENCES//IN PERSON INTERVIEW//MULTI CRITERIA DECISION ANALYSIS 15 67 22%
COST EFFECTIVENESS RATIOS//NET HEALTH BENEFIT//COST EFFECTIVENESS ACCEPTABILITY CURVES 14 74 19%
COVERAGE WITH EVIDENCE DEVELOPMENT//MEDICARE COVERAGE//RISK SHARING AGREEMENTS 14 91 15%
HORIZON SCANNING SYSTEMS//HORIZON SCANNING//EARLY AWARENESS AND ALERT SYSTEMS 12 20 60%
COMPARATIVE EFFECTIVENESS RESEARCH//PATIENT CENTERED OUTCOMES RESEARCH//ELECTRONIC CLINICAL DATA 10 158 6%

ADAPTIVE DESIGN//GROUP SEQUENTIAL TEST//GROUP SEQUENTIAL DESIGN 58 221 26%
CONTINUAL REASSESSMENT METHOD//DOSE FINDING//DOSE FINDING STUDIES 50 200 25%
TWO STAGE DESIGN//PHASE II DESIGN//PHASE II CLINICAL TRIALS 28 113 25%
FAMILYWISE ERROR RATE//GATEKEEPING PROCEDURE//MULTIPLE TESTS 27 119 23%
SCORE INTERVAL//BINOMIAL PROPORTION//BINOMIAL DISTRIBUTION 18 140 13%
NONINFERIORITY MARGIN//NON INFERIORITY//NON INFERIORITY TRIAL 16 112 14%
MONOTONE MISSING//DISCRETE TIME LONGITUDINAL DATA//INDEPENDENT MISSING 12 37 32%
MINIMUM EFFECTIVE DOSE//MCP MOD//WILLIAMS TEST 12 57 21%
META ANALYTIC PREDICTIVE//EPSILON INFORMATION PRIOR//COMPUTATIONALLY INTENSIVE METHODS 42 21%
MULTIREGIONAL CLINICAL TRIAL//BRIDGING STUDY//MULTIREGIONAL TRIAL 68 12%

MISSING DATA//MULTIPLE IMPUTATION//GENERALIZED ESTIMATING EQUATIONS
GENERALIZED ESTIMATING EQUATIONS//QUASI LEAST SQUARES//GEE 23 104 22%
MULTIPLE IMPUTATION//MISSING DATA//PREDICTIVE MEAN MATCHING 23 218 11%
JOINT MODEL//SHARED PARAMETER MODEL//DYNAMIC PREDICTIONS 22 112 20%
CONCORDANCE CORRELATION COEFFICIENT//TOTAL DEVIATION INDEX//COEFFICIENT OF INDIVIDUAL AGREEMENT 19 66 29%
PATTERN MIXTURE MODEL//MISSING NOT AT RANDOM//MISSING DATA 19 137 14%
ZERO INFLATION//ZERO INFLATED MODELS//OVERDISPERSION 16 142 11%
CENSORED COVARIATE//CENSORED PREDICTOR//TWO PART STATISTICS 13 41 32%
REGRESSION CALIBRATION//MEASUREMENT ERROR//CORRECTED SCORE 12 105 11%
INFORMATIVE CLUSTER SIZE//WITHIN CLUSTER RESAMPLING//CLUSTERED OBSERVATIONS 10 43 23%
DOUBLE ROBUSTNESS//AUGMENTED INVERSE PROBABILITY WEIGHTING AIPW//MISSING AT RANDOM 10 67 15%

COMPETING RISKS//INTERVAL CENSORING//COUNTING PROCESS
INTEGRATED DISCRIMINATION IMPROVEMENT//NET RECLASSIFICATION IMPROVEMENT//DECISION ANALYTIC MEASURES 28 110 25%
MULTISTATE MODEL//ILLNESS DEATH PROCESS//AALEN JOHANSEN ESTIMATOR 23 111 21%
COMPETING RISKS//CUMULATIVE INCIDENCE FUNCTION//CAUSE SPECIFIC HAZARD 20 117 17%
RECURRENT EVENTS//PANEL COUNT DATA//INFORMATIVE OBSERVATION TIMES 19 174 11%
EXPLAINED VARIATION//TIME DEPENDENT ROC//C INDEX 19 68 28%
CURE RATE MODEL//CURE MODEL//LONG TERM SURVIVAL MODELS 17 95 18%
SURROGATE ENDPOINT//PRENTICE CRITERION//LIKELIHOOD REDUCTION FACTOR 13 84 15%
INTERVAL CENSORING//CURRENT STATUS DATA//INTERVAL CENSORED DATA 13 127 10%
CASE COHORT DESIGN//CASE COHORT//CASE COHORT STUDY 12 77 16%
FRAILTY MODEL//CORRELATED FAILURE TIMES//CROSS RATIO FUNCTION 12 104 12%

EVIDENCE-BASED MEDICINE//PUBLICATION BIAS//ABSTRACT
MULTIVARIATE META-ANALYSIS//DERSIMONIAN LAIRD ESTIMATOR//MANDEL PAULE ALGORITHM 40 150 27%
MEDICAL EPISTEMOLOGY//EVIDENCE-BASED MEDICINE//EVIDENCE IN MEDICINE 32 77 42%
MIXED TREATMENT COMPARISON//NETWORK META-ANALYSIS//MULTIPLE TREATMENTS META-ANALYSIS 26 198 13%
MEDLINE//EMBASE//LITERATURE SEARCHING 11 112 10%
NUMBER NEEDED TO TREAT//ABSOLUTE RISK REDUCTION//NUMBER NEEDED TO TREAT NNT 52 17%
TRIAL REGISTRATION//CLINICALTRIALSGOV//PUBLICATION BIAS 250 3%
PUBLICATION BIAS//FUNNEL PLOT//SMALL STUDY EFFECTS 64 9%
JOURNAL CLUB//EVIDENCE-BASED MEDICINE EDUCATION//FRESNO TEST 155 4%
AWARENESS SCORE//CHIROPRACTIC QUESTIONNAIRES//COMMUNITY OF PRACTICE KNOWLEDGE NETWORKS 45 13%
CONFLICT OF INTEREST//EDITORIAL ETHICS//CONFLICTS OF INTEREST 189 3%

PATIENT SAFETY//MEDICATION ERRORS//MEDICAL ERRORS
MEDICATION ERRORS//SMART PUMPS//MEDICATION ADMINISTRATION ERRORS 25 281 9%
SIGN OUT//HANDOFF//HANDOVER 19 334 6%
VOCERA//HOSPITAL COMMUNICATION SYSTEMS//PAGERS 19 66 29%
MEDWISE//THREAT AND ERROR MANAGEMENT TEM//USER CONFIGURABLE EHR 11 32 34%
INCIDENT REPORTING//MEDICATION INCIDENTS//ERROR REPORTING 155 5%
MEDICAL DEVICE DESIGN//INSTITUTIONAL DECISION MAKING//USER COMPUTER 34 24%
NON TECHNICAL SKILLS//TEAMWORK//TEAM TRAINING 317 2%
TRIGGER TOOL//GLOBAL TRIGGER TOOL//PREVENTABLE HARM 182 3%

TELEMEDICINE//TELEHEALTH//TELEPATHOLOGY
TELEHEALTH//TELECARE//TELEHEALTHCARE 32 188 17%
TELEMONITORING//HOME TELEMONITORING//TETEMONITORING 27 155 17%
ELDERCARE TECHNOLOGY//HOME BASED CLINICAL ASSESSMENT//PASSIVE INFRARED PIR MOTION DETECTORS 19 90 21%
TELE ECHOGRAPHY//TELESONOGRAPHY//TELE ULTRASOUND 10 48 21%
MOBILE TELEMEDICINE//MOBILE CARE//TIME FREQUENCY ENERGY DISTRIBUTIONS 34 21%
CHRONIC DISEASE METHODS THERAPY//CRITICAL PATHWAYS MESH//HEATH CARE PRACTICES 24 29%
TELEREHABILITATION//TELEPRACTICE//REMOTE ASSESSMENT 90 7%
TELE EEG//INITIATE BUILD OPERATE TRANSFER STRATEGY//INTERNATIONAL VIRTUAL E HOSPITAL FOUNDATION 69 7%
ISI WEB OF SCIENCE DATABASE//LISTENING STYLES//NON ADHERENCE FACTORS 24 21%
TELEDERMATOLOGY//MOBILE TELEDERMATOLOGY//STORE AND FORWARD 135 3%

CAUSAL INFERENCE//PROPENSITY SCORE//PRINCIPAL STRATIFICATION
PROPENSITY SCORE//OBSERVATIONAL STUDY//COVARIATE BALANCE 34 229 15%
PRINCIPAL STRATIFICATION//NONCOMPLIANCE//CAUSAL INFERENCE 32 159 20%
MARGINAL STRUCTURAL MODELS//TARGETED MAXIMUM LIKELIHOOD ESTIMATION//CAUSAL INFERENCE 29 221 13%
DYNAMIC TREATMENT REGIMES//ADAPTIVE TREATMENT STRATEGIES//OPTIMAL TREATMENT REGIME 19 127 15%
MENDELIAN RANDOMIZATION//MENDELIAN RANDOMISATION//ALLELE SCORES 11 121 9%
PROPENSITY SCORE CALIBRATION//PROBABILISTIC BIAS ANALYSIS//NONDIFFERENTIAL 50 8%
RANDOMIZATION INFERENCE//MATCHED SAMPLING//FINE BALANCE 56 7%
INSTRUMENTAL VARIABLES//PHYSICIAN PRESCRIBING PREFERENCE//PHYSICIANS PRESCRIBING PREFERENCE 64 6%
MARGINAL TREATMENT EFFECT//CORRELATED RANDOM COEFFICIENT MODEL//LOCAL INSTRUMENTAL VARIABLES 51 2%
UNCONFOUNDEDNESS//PROPENSITY SCORE MATCHING//SELECTION ON OBSERVABLES 204 0%
SPECIALTY# articles in Pmi# articles in topicShare of topic in Pmi
TOPIC
ELECTRONIC HEALTH RECORDS//ELECTRONIC MEDICAL RECORD//MEDICAL INFORMATICS
NATURAL LANGUAGE PROCESSING//MEDICAL LANGUAGE PROCESSING//CLINICAL TEXT 188 278 68%
HEALTH INFORMATION TECHNOLOGY//ELECTRONIC HEALTH RECORDS//MEANINGFUL USE 127 392 32%
CDISC//ISO IEC 11179//CLINICAL RESEARCH INFORMATICS 112 167 67%
ALERT FATIGUE//CLINICAL DECISION SUPPORT SYSTEMS//CLINICAL DECISION SUPPORT 110 216 51%
NURSING INFORMATION SYSTEM//CLINICAL INFORMATION SYSTEMS//DOCUMENTATION TIME 104 152 68%
OPENEHR//LOINC//CLINICAL ARCHETYPES 89 111 80%
HEALTH INFORMATION EXCHANGE//HEALTH RECORD BANK//REGIONAL HEALTH INFORMATION ORGANIZATIONS 87 154 56%
CPOE//E PRESCRIBING//ELECTRONIC PRESCRIBING 84 218 39%
SNOMED CT//UMLS//ABSTRACTION NETWORK 76 108 70%
PHEWAS//PHENOME WIDE ASSOCIATION STUDY//CLINICAL PHENOTYPE MODELING 49 160 31%

HEALTH LITERACY//INTERNET//MHEALTH
INTERNET//HEALTH INFORMATION//ONLINE HEALTH INFORMATION 48 193 25%
ONLINE SUPPORT GROUPS//COMPREHENSIVE HEALTH ENHANCEMENT SUPPORT SYSTEM CHESS//INTERNET CANCER SUPPORT GROUPS 37 220 17%
MEDICAL APP//APPS//SMARTPHONE 33 165 20%
MHEALTH//MEDICATION REMINDERS//REAL TIME ADHERENCE MONITORING 32 275 12%
E PROFESSIONALISM//SOCIAL MEDIA//TWITTER MESSAGING 30 274 11%
TEXT MESSAGING//TEXT MESSAGE//MHEALTH 29 218 13%
MOBILE APPS//APPS//MHEALTH 25 126 20%
PHYSICIAN RATING WEBSITE//RATING SITES//QUALITY TRANSPARENCY 23 61 38%

HEALTH TECHNOLOGY ASSESSMENT//EQ 5D//PRIORITY SETTING
HEALTH TECHNOLOGY ASSESSMENT//HOSPITAL BASED HTA//MINI HTA 58 118 49%
EQ 5D//SF 6D//EQ 5D 5L 38 411 9%
VALUE OF INFORMATION//OPTIMAL TRIAL DESIGN//VALUE OF INFORMATION ANALYSIS 29 95 31%
HEALTH TECHNOLOGY ASSESSMENT//INSTITUTE FOR QUALITY AND EFFICIENCY IN HEALTH CARE//FOURTH HURDLE 28 153 18%
DYNAMIC TRANSMISSION//HALF CYCLE CORRECTION//COST EFFECTIVENESS MODELING 26 82 32%
STRENGTH OF PREFERENCES//IN PERSON INTERVIEW//MULTI CRITERIA DECISION ANALYSIS 15 67 22%
COST EFFECTIVENESS RATIOS//NET HEALTH BENEFIT//COST EFFECTIVENESS ACCEPTABILITY CURVES 14 74 19%
COVERAGE WITH EVIDENCE DEVELOPMENT//MEDICARE COVERAGE//RISK SHARING AGREEMENTS 14 91 15%
HORIZON SCANNING SYSTEMS//HORIZON SCANNING//EARLY AWARENESS AND ALERT SYSTEMS 12 20 60%
COMPARATIVE EFFECTIVENESS RESEARCH//PATIENT CENTERED OUTCOMES RESEARCH//ELECTRONIC CLINICAL DATA 10 158 6%

ADAPTIVE DESIGN//GROUP SEQUENTIAL TEST//GROUP SEQUENTIAL DESIGN 58 221 26%
CONTINUAL REASSESSMENT METHOD//DOSE FINDING//DOSE FINDING STUDIES 50 200 25%
TWO STAGE DESIGN//PHASE II DESIGN//PHASE II CLINICAL TRIALS 28 113 25%
FAMILYWISE ERROR RATE//GATEKEEPING PROCEDURE//MULTIPLE TESTS 27 119 23%
SCORE INTERVAL//BINOMIAL PROPORTION//BINOMIAL DISTRIBUTION 18 140 13%
NONINFERIORITY MARGIN//NON INFERIORITY//NON INFERIORITY TRIAL 16 112 14%
MONOTONE MISSING//DISCRETE TIME LONGITUDINAL DATA//INDEPENDENT MISSING 12 37 32%
MINIMUM EFFECTIVE DOSE//MCP MOD//WILLIAMS TEST 12 57 21%
META ANALYTIC PREDICTIVE//EPSILON INFORMATION PRIOR//COMPUTATIONALLY INTENSIVE METHODS 42 21%
MULTIREGIONAL CLINICAL TRIAL//BRIDGING STUDY//MULTIREGIONAL TRIAL 68 12%

MISSING DATA//MULTIPLE IMPUTATION//GENERALIZED ESTIMATING EQUATIONS
GENERALIZED ESTIMATING EQUATIONS//QUASI LEAST SQUARES//GEE 23 104 22%
MULTIPLE IMPUTATION//MISSING DATA//PREDICTIVE MEAN MATCHING 23 218 11%
JOINT MODEL//SHARED PARAMETER MODEL//DYNAMIC PREDICTIONS 22 112 20%
CONCORDANCE CORRELATION COEFFICIENT//TOTAL DEVIATION INDEX//COEFFICIENT OF INDIVIDUAL AGREEMENT 19 66 29%
PATTERN MIXTURE MODEL//MISSING NOT AT RANDOM//MISSING DATA 19 137 14%
ZERO INFLATION//ZERO INFLATED MODELS//OVERDISPERSION 16 142 11%
CENSORED COVARIATE//CENSORED PREDICTOR//TWO PART STATISTICS 13 41 32%
REGRESSION CALIBRATION//MEASUREMENT ERROR//CORRECTED SCORE 12 105 11%
INFORMATIVE CLUSTER SIZE//WITHIN CLUSTER RESAMPLING//CLUSTERED OBSERVATIONS 10 43 23%
DOUBLE ROBUSTNESS//AUGMENTED INVERSE PROBABILITY WEIGHTING AIPW//MISSING AT RANDOM 10 67 15%

COMPETING RISKS//INTERVAL CENSORING//COUNTING PROCESS
INTEGRATED DISCRIMINATION IMPROVEMENT//NET RECLASSIFICATION IMPROVEMENT//DECISION ANALYTIC MEASURES 28 110 25%
MULTISTATE MODEL//ILLNESS DEATH PROCESS//AALEN JOHANSEN ESTIMATOR 23 111 21%
COMPETING RISKS//CUMULATIVE INCIDENCE FUNCTION//CAUSE SPECIFIC HAZARD 20 117 17%
RECURRENT EVENTS//PANEL COUNT DATA//INFORMATIVE OBSERVATION TIMES 19 174 11%
EXPLAINED VARIATION//TIME DEPENDENT ROC//C INDEX 19 68 28%
CURE RATE MODEL//CURE MODEL//LONG TERM SURVIVAL MODELS 17 95 18%
SURROGATE ENDPOINT//PRENTICE CRITERION//LIKELIHOOD REDUCTION FACTOR 13 84 15%
INTERVAL CENSORING//CURRENT STATUS DATA//INTERVAL CENSORED DATA 13 127 10%
CASE COHORT DESIGN//CASE COHORT//CASE COHORT STUDY 12 77 16%
FRAILTY MODEL//CORRELATED FAILURE TIMES//CROSS RATIO FUNCTION 12 104 12%

EVIDENCE-BASED MEDICINE//PUBLICATION BIAS//ABSTRACT
MULTIVARIATE META-ANALYSIS//DERSIMONIAN LAIRD ESTIMATOR//MANDEL PAULE ALGORITHM 40 150 27%
MEDICAL EPISTEMOLOGY//EVIDENCE-BASED MEDICINE//EVIDENCE IN MEDICINE 32 77 42%
MIXED TREATMENT COMPARISON//NETWORK META-ANALYSIS//MULTIPLE TREATMENTS META-ANALYSIS 26 198 13%
MEDLINE//EMBASE//LITERATURE SEARCHING 11 112 10%
NUMBER NEEDED TO TREAT//ABSOLUTE RISK REDUCTION//NUMBER NEEDED TO TREAT NNT 52 17%
TRIAL REGISTRATION//CLINICALTRIALSGOV//PUBLICATION BIAS 250 3%
PUBLICATION BIAS//FUNNEL PLOT//SMALL STUDY EFFECTS 64 9%
JOURNAL CLUB//EVIDENCE-BASED MEDICINE EDUCATION//FRESNO TEST 155 4%
AWARENESS SCORE//CHIROPRACTIC QUESTIONNAIRES//COMMUNITY OF PRACTICE KNOWLEDGE NETWORKS 45 13%
CONFLICT OF INTEREST//EDITORIAL ETHICS//CONFLICTS OF INTEREST 189 3%

PATIENT SAFETY//MEDICATION ERRORS//MEDICAL ERRORS
MEDICATION ERRORS//SMART PUMPS//MEDICATION ADMINISTRATION ERRORS 25 281 9%
SIGN OUT//HANDOFF//HANDOVER 19 334 6%
VOCERA//HOSPITAL COMMUNICATION SYSTEMS//PAGERS 19 66 29%
MEDWISE//THREAT AND ERROR MANAGEMENT TEM//USER CONFIGURABLE EHR 11 32 34%
INCIDENT REPORTING//MEDICATION INCIDENTS//ERROR REPORTING 155 5%
MEDICAL DEVICE DESIGN//INSTITUTIONAL DECISION MAKING//USER COMPUTER 34 24%
NON TECHNICAL SKILLS//TEAMWORK//TEAM TRAINING 317 2%
TRIGGER TOOL//GLOBAL TRIGGER TOOL//PREVENTABLE HARM 182 3%

TELEMEDICINE//TELEHEALTH//TELEPATHOLOGY
TELEHEALTH//TELECARE//TELEHEALTHCARE 32 188 17%
TELEMONITORING//HOME TELEMONITORING//TETEMONITORING 27 155 17%
ELDERCARE TECHNOLOGY//HOME BASED CLINICAL ASSESSMENT//PASSIVE INFRARED PIR MOTION DETECTORS 19 90 21%
TELE ECHOGRAPHY//TELESONOGRAPHY//TELE ULTRASOUND 10 48 21%
MOBILE TELEMEDICINE//MOBILE CARE//TIME FREQUENCY ENERGY DISTRIBUTIONS 34 21%
CHRONIC DISEASE METHODS THERAPY//CRITICAL PATHWAYS MESH//HEATH CARE PRACTICES 24 29%
TELEREHABILITATION//TELEPRACTICE//REMOTE ASSESSMENT 90 7%
TELE EEG//INITIATE BUILD OPERATE TRANSFER STRATEGY//INTERNATIONAL VIRTUAL E HOSPITAL FOUNDATION 69 7%
ISI WEB OF SCIENCE DATABASE//LISTENING STYLES//NON ADHERENCE FACTORS 24 21%
TELEDERMATOLOGY//MOBILE TELEDERMATOLOGY//STORE AND FORWARD 135 3%

CAUSAL INFERENCE//PROPENSITY SCORE//PRINCIPAL STRATIFICATION
PROPENSITY SCORE//OBSERVATIONAL STUDY//COVARIATE BALANCE 34 229 15%
PRINCIPAL STRATIFICATION//NONCOMPLIANCE//CAUSAL INFERENCE 32 159 20%
MARGINAL STRUCTURAL MODELS//TARGETED MAXIMUM LIKELIHOOD ESTIMATION//CAUSAL INFERENCE 29 221 13%
DYNAMIC TREATMENT REGIMES//ADAPTIVE TREATMENT STRATEGIES//OPTIMAL TREATMENT REGIME 19 127 15%
MENDELIAN RANDOMIZATION//MENDELIAN RANDOMISATION//ALLELE SCORES 11 121 9%
PROPENSITY SCORE CALIBRATION//PROBABILISTIC BIAS ANALYSIS//NONDIFFERENTIAL 50 8%
RANDOMIZATION INFERENCE//MATCHED SAMPLING//FINE BALANCE 56 7%
INSTRUMENTAL VARIABLES//PHYSICIAN PRESCRIBING PREFERENCE//PHYSICIANS PRESCRIBING PREFERENCE 64 6%
MARGINAL TREATMENT EFFECT//CORRELATED RANDOM COEFFICIENT MODEL//LOCAL INSTRUMENTAL VARIABLES 51 2%
UNCONFOUNDEDNESS//PROPENSITY SCORE MATCHING//SELECTION ON OBSERVABLES 204 0%

## Author notes

Handling Editor: Vincent Larivière

This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. For a full description of the license, please visit https://creativecommons.org/licenses/by/4.0/legalcode.