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Table 3. 
Regression results from the APC OA hurdle models for Agricultural Sciences, Biological and Biomedical Sciences, Business, and Education, showing the count data component (APC OA articles > 0) and the zero count component (APC OA articles = 0)
 Agricultural SciencesBiological & Biomedical Sci.BusinessEducation
βSig.e^βStd. Err.βSig.e^βStd. Err.βSig.e^βStd. Err.βSig.e^βStd. Err.
  Positive Count Component Positive Count Component Positive Count Component Positive Count Component 
Gender is Male 0.094 * 1.099 0.040 0.102 *** 1.107 0.011 0.058   1.059 0.654 0.285 *** 1.329 0.085 
Institution is Public −0.187 * 0.829 0.091 −0.029   0.971 0.010 −0.090   0.914 0.459 −0.035   0.965 0.109 
Institution is AAU Member −0.006   0.994 0.036 0.095 *** 1.100 0.010 −0.022   0.978 0.855 −0.003   0.997 0.089 
Years Since Degree −0.003   0.997 0.002 −0.009 *** 0.991 0.001 0.022 *** 1.022 0.001 0.003   1.003 0.006 
Professorial Rank −0.005   0.995 0.032 0.147 *** 1.158 0.009 −0.327 ** 0.721 0.001 −0.040   0.961 0.076 
Has Won Research Grants 0.314 *** 1.368 0.038 0.223 *** 1.249 0.010 0.581 *** 1.788 0.002 0.278 * 1.321 0.109 
Total Article Count 0.040 *** 1.041 0.001 0.024 *** 1.024 0.000 0.087 *** 1.091 0.000 0.070 *** 1.073 0.007 
Log(θ) 0.409 *** 1.506 0.054 1.000 *** 2.718 0.016 −4.122   0.016 0.387 −1.038 *** 0.354 0.309 
Constant 0.547 *** 1.728 0.110 0.788 *** 2.198 0.019 −4.554   0.011 4.730 −1.745 *** 0.175 0.306 
  Zero Hurdle Component Zero Hurdle Component Zero Hurdle Component Zero Hurdle Component 
Gender is Male 0.039   1.040 0.086 0.116 ** 1.123 0.041 −0.045   0.956 0.067 0.168 ** 1.183 0.058 
Institution is Public −0.521 * 0.594 0.264 0.023   1.023 0.043 −0.241 *** 0.786 0.064 0.095   1.100 0.077 
Institution is AAU Member 0.010   1.010 0.081 0.133 ** 1.143 0.041 −0.004   0.996 0.063 0.089   1.093 0.062 
Years Since Degree 0.004   1.004 0.005 −0.013 *** 0.987 0.002 0.004   1.004 0.003 −0.006   0.994 0.004 
Professorial Rank −0.143 ** 0.866 0.073 −0.005   0.995 0.034 0.024   1.024 0.054 −0.016   0.984 0.051 
Has Won Research Grants 0.381 *** 1.463 0.111 0.723 *** 2.060 0.047 1.397 *** 4.045 0.134 0.263 ** 1.300 0.088 
Total Article Count 0.206 *** 1.229 0.008 0.250 *** 1.284 0.005 0.113 *** 1.119 0.004 0.129 *** 1.138 0.005 
Constant −0.345   0.708 0.292 −0.482 *** 0.618 0.069 −2.680 *** 0.069 0.112 −2.062 *** 0.127 0.110 
Observations 4,860       30,725       11,764       8,317       
Log-likelihood −9,954       −75,120       −5,786       −6,228       
 Agricultural SciencesBiological & Biomedical Sci.BusinessEducation
βSig.e^βStd. Err.βSig.e^βStd. Err.βSig.e^βStd. Err.βSig.e^βStd. Err.
  Positive Count Component Positive Count Component Positive Count Component Positive Count Component 
Gender is Male 0.094 * 1.099 0.040 0.102 *** 1.107 0.011 0.058   1.059 0.654 0.285 *** 1.329 0.085 
Institution is Public −0.187 * 0.829 0.091 −0.029   0.971 0.010 −0.090   0.914 0.459 −0.035   0.965 0.109 
Institution is AAU Member −0.006   0.994 0.036 0.095 *** 1.100 0.010 −0.022   0.978 0.855 −0.003   0.997 0.089 
Years Since Degree −0.003   0.997 0.002 −0.009 *** 0.991 0.001 0.022 *** 1.022 0.001 0.003   1.003 0.006 
Professorial Rank −0.005   0.995 0.032 0.147 *** 1.158 0.009 −0.327 ** 0.721 0.001 −0.040   0.961 0.076 
Has Won Research Grants 0.314 *** 1.368 0.038 0.223 *** 1.249 0.010 0.581 *** 1.788 0.002 0.278 * 1.321 0.109 
Total Article Count 0.040 *** 1.041 0.001 0.024 *** 1.024 0.000 0.087 *** 1.091 0.000 0.070 *** 1.073 0.007 
Log(θ) 0.409 *** 1.506 0.054 1.000 *** 2.718 0.016 −4.122   0.016 0.387 −1.038 *** 0.354 0.309 
Constant 0.547 *** 1.728 0.110 0.788 *** 2.198 0.019 −4.554   0.011 4.730 −1.745 *** 0.175 0.306 
  Zero Hurdle Component Zero Hurdle Component Zero Hurdle Component Zero Hurdle Component 
Gender is Male 0.039   1.040 0.086 0.116 ** 1.123 0.041 −0.045   0.956 0.067 0.168 ** 1.183 0.058 
Institution is Public −0.521 * 0.594 0.264 0.023   1.023 0.043 −0.241 *** 0.786 0.064 0.095   1.100 0.077 
Institution is AAU Member 0.010   1.010 0.081 0.133 ** 1.143 0.041 −0.004   0.996 0.063 0.089   1.093 0.062 
Years Since Degree 0.004   1.004 0.005 −0.013 *** 0.987 0.002 0.004   1.004 0.003 −0.006   0.994 0.004 
Professorial Rank −0.143 ** 0.866 0.073 −0.005   0.995 0.034 0.024   1.024 0.054 −0.016   0.984 0.051 
Has Won Research Grants 0.381 *** 1.463 0.111 0.723 *** 2.060 0.047 1.397 *** 4.045 0.134 0.263 ** 1.300 0.088 
Total Article Count 0.206 *** 1.229 0.008 0.250 *** 1.284 0.005 0.113 *** 1.119 0.004 0.129 *** 1.138 0.005 
Constant −0.345   0.708 0.292 −0.482 *** 0.618 0.069 −2.680 *** 0.069 0.112 −2.062 *** 0.127 0.110 
Observations 4,860       30,725       11,764       8,317       
Log-likelihood −9,954       −75,120       −5,786       −6,228       

* p < 0.05; ** p < 0.01; *** p < 0.001.

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