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Table 5. 
Regression results from the APC OA hurdle models for Natural Resources and Conservation, Physical and Mathematical Sciences, and Social and Behavioral Sciences, showing the count data component (APC OA articles > 0) and the zero count component (APC OA articles = 0)
 Nat. Res. & ConservationPhys. & Math. Sci.Soc. & Behav. Sci.
βSig.e^βStd. Err.βSig.e^βStd. Err.βSig.e^βStd. Err.
  Positive Count Component Positive Count Component Positive Count Component 
Gender is Male 0.031   1.031 0.036 0.069 ** 1.072 0.022 0.138 *** 1.147 0.032 
Institution is Public −0.035   0.966 0.045 −0.079 *** 0.924 0.021 0.043   1.044 0.034 
Institution is AAU Member 0.038   1.039 0.032 0.174 *** 1.190 0.019 0.145 *** 1.156 0.032 
Years Since Degree −0.005 ** 0.995 0.002 −0.003 * 0.997 0.001 0.007 *** 1.007 0.002 
Professorial Rank 0.021   1.021 0.028 0.126 *** 1.134 0.016 −0.157 *** 0.855 0.028 
Has Won Research Grants 0.177 *** 1.193 0.032 0.225 *** 1.253 0.018 0.374 *** 1.453 0.034 
Total Article Count 0.036 *** 1.036 0.001 0.018 *** 1.018 0.000 0.061 *** 1.063 0.002 
Log(θ) 0.967 *** 2.631 0.054 −0.348 *** 0.706 0.027 −0.653 *** 0.521 0.063 
Constant 0.653 *** 1.921 0.070 0.368 *** 1.446 0.040 −0.919 *** 0.399 0.075 
  Zero Hurdle Component Zero Hurdle Component Zero Hurdle Component 
Gender is Male −0.208   0.812 0.109 −0.011   0.989 0.037 0.044   1.045 0.030 
Institution is Public 0.167   1.182 0.165 0.050   1.052 0.035 0.099 ** 1.104 0.034 
Institution is AAU Member −0.079   0.924 0.106 0.016   1.016 0.032 0.185 *** 1.203 0.031 
Years Since Degree −0.002   0.998 0.006 −0.010 *** 0.990 0.002 0.003   1.003 0.002 
Professorial Rank −0.129   0.879 0.088 −0.008   0.992 0.027 −0.117 *** 0.890 0.028 
Has Won Research Grants 0.280 * 1.323 0.123 0.267 *** 1.306 0.033 0.686 *** 1.985 0.041 
Total Article Count 0.254 *** 1.289 0.011 0.177 *** 1.194 0.003 0.141 *** 1.152 0.002 
Constant −0.919 *** 0.399 0.224 −0.953 *** 0.385 0.060 −1.927 *** 0.146 0.056 
Observations 3,913       30,415       28,228       
Log-likelihood −8,287       −65,540       −32,000       
 Nat. Res. & ConservationPhys. & Math. Sci.Soc. & Behav. Sci.
βSig.e^βStd. Err.βSig.e^βStd. Err.βSig.e^βStd. Err.
  Positive Count Component Positive Count Component Positive Count Component 
Gender is Male 0.031   1.031 0.036 0.069 ** 1.072 0.022 0.138 *** 1.147 0.032 
Institution is Public −0.035   0.966 0.045 −0.079 *** 0.924 0.021 0.043   1.044 0.034 
Institution is AAU Member 0.038   1.039 0.032 0.174 *** 1.190 0.019 0.145 *** 1.156 0.032 
Years Since Degree −0.005 ** 0.995 0.002 −0.003 * 0.997 0.001 0.007 *** 1.007 0.002 
Professorial Rank 0.021   1.021 0.028 0.126 *** 1.134 0.016 −0.157 *** 0.855 0.028 
Has Won Research Grants 0.177 *** 1.193 0.032 0.225 *** 1.253 0.018 0.374 *** 1.453 0.034 
Total Article Count 0.036 *** 1.036 0.001 0.018 *** 1.018 0.000 0.061 *** 1.063 0.002 
Log(θ) 0.967 *** 2.631 0.054 −0.348 *** 0.706 0.027 −0.653 *** 0.521 0.063 
Constant 0.653 *** 1.921 0.070 0.368 *** 1.446 0.040 −0.919 *** 0.399 0.075 
  Zero Hurdle Component Zero Hurdle Component Zero Hurdle Component 
Gender is Male −0.208   0.812 0.109 −0.011   0.989 0.037 0.044   1.045 0.030 
Institution is Public 0.167   1.182 0.165 0.050   1.052 0.035 0.099 ** 1.104 0.034 
Institution is AAU Member −0.079   0.924 0.106 0.016   1.016 0.032 0.185 *** 1.203 0.031 
Years Since Degree −0.002   0.998 0.006 −0.010 *** 0.990 0.002 0.003   1.003 0.002 
Professorial Rank −0.129   0.879 0.088 −0.008   0.992 0.027 −0.117 *** 0.890 0.028 
Has Won Research Grants 0.280 * 1.323 0.123 0.267 *** 1.306 0.033 0.686 *** 1.985 0.041 
Total Article Count 0.254 *** 1.289 0.011 0.177 *** 1.194 0.003 0.141 *** 1.152 0.002 
Constant −0.919 *** 0.399 0.224 −0.953 *** 0.385 0.060 −1.927 *** 0.146 0.056 
Observations 3,913       30,415       28,228       
Log-likelihood −8,287       −65,540       −32,000       

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

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