This paper presents an analysis of the Overton policy document database, describing the makeup of materials indexed and the nature in which they cite academic literature. We report on various aspects of the data, including growth, geographic spread, language representation, the range of policy source types included, and the availability of citation links in documents. Longitudinal analysis over established journal category schemes is used to reveal the scale and disciplinary focus of citations and determine the feasibility of developing field-normalized citation indicators. To corroborate the data indexed, we also examine how well self-reported funding outcomes collected by UK funders correspond to data indexed in the Overton database. Finally, to test the data in an experimental setting, we assess whether peer-review assessment of impact as measured by the UK Research Excellence Framework (REF) 2014 correlates with derived policy citation metrics. Our findings show that for some research topics, such as health, economics, social care, and the environment, Overton contains a core set of policy documents with sufficient citation linkage to academic literature to support various citation analyses that may be informative in research evaluation, impact assessment, and policy review.

We examine the hypothesis that research collaboration has enabled a global research network to evolve, with self-organizing properties transcending national research policy. We examine research output, bilateral and multilateral collaboration, subject diversity, and citation impact over 40 years, in detail for the G7 and BRICK groups of countries and in summary for 26 other nations. We find that the rise in national output was strongly associated with bilateral collaboration until the 2000s but after that by multilateral partnerships, with the shift happening at much the same time across countries. There was a general increase in research subject diversity, with evenness across subjects converging on a similar index value for many countries. Similar diversity is not the same as actual similarity but, in fact, the G7 countries became increasingly similar. National average citation impact (CNCI) rose and groups converged on similar impact values. The impact of the largest economies is above world average, which is a phenomenon we discuss separately. The similarities in patterns and timing occur across countries despite variance in their research policies, such as research assessment. We suggest that the key agent facilitating global network self-organization is a shared concept of best practice in research.

National research diversity is explored through the balance of global and national papers in journal categories in the Web of Science (WoS) and Essential Science Indicators (ESI) and we examine the consequences of “normalizing” national publication counts against global baselines. Global balance across subject categories became more even as annual WoS indexing grew fourfold between 1981 and 2018, with a relative shift from biomedicine towards environment and technology. Change at the country level may have tracked this or been influenced by local policy and funding. We discuss choice of methods and indices for analysis: WoS categories provide better granularity than ESI; Lorenz curves are explored but found limiting; the Pratt index, Gini coefficient, and Shannon diversity are compared. At the national level, balance generally increases and is greatest in non-Anglophone countries, perhaps due to shifts in language and journal use. Two aspects of national change are revealed: the balance of actual WoS paper counts and the balance of counts normalized against world baseline. The broad patterns for these analyses are similar, but normalized data indicate relatively greater evenness. National patterns link to research capacity and regional networking opportunities, while international collaboration may blend national differences. A data set is provided for analytical use.