## 4 Performance and Collaboration Analyses Results
### Analyses of Country/Region, Institution, and Author
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Journal/Conference** & **H** & **A (R)** & **TC** & **ACP** & \(\geq\)**100** & \(\geq\)**50** & **A1** & **A2** \\ \hline _Journal of Biomedical Informatics_ & 20 & 37 (1) & 1224 & 33.08 & 3 & 7 & 1 & 36 \\ _Journal of the American Medical Informatics Association_ & 17 & 23 (3) & 1357 & 59 & 2 & 5 & 7 & 16 \\ _American Medical Informatics Association_ (_AMIA) _Annual_ & 12 & 22 (4) & 315 & 14.32 & 0 & 0 & 13 & 9 \\ _Lecture Notes in Computer Science_ & 9 & 16 (5) & 222 & 13.88 & 0 & 1 & 4 & 12 \\ _Studies in Health Technology and Informatics_ & 8 & 26 (2) & 258 & 9.92 & 0 & 0 & 4 & 22 \\ _BMC Medical Informatics and Decision Making_ & 7 & 11 (6) & 175 & 15.91 & 0 & 1 & 1 & 10 \\ _Artificial Intelligence in Medicine_ & 6 & 7 (12) & 290 & 41.43 & 0 & 2 & 1 & 6 \\ _International Journal of Medical Informatics_ & 6 & 8 (7) & 123 & 15.38 & 0 & 0 & 1 & 7 \\ _PLoS ONE_ & 6 & 8 (7) & 101 & 12.63 & 0 & 0 & 0 & 8 \\ _Methods of Information in Medicine_ & 5 & 8 (7) & 81 & 10.13 & 0 & 0 & 2 & 6 \\ _BMC Bioinformatics_ & 4 & 4 (14) & 147 & 36.75 & 0 & 1 & 0 & 4 \\ _World Congress on Medical and Health Informatics_ (_MEDINFO_) & 4 & 8 (7) & 61 & 7.63 & 0 & 0 & 3 & 5 \\ _International Conference on Health Informatics_ (_HELATHINF_) & 4 & 8 (7) & 52 & 6.5 & 0 & 0 & 3 & 5 \\ \hline \hline \end{tabular}
\begin{tabular}{c} Abbreviations: H: H-index; A: Article count; R: Ranking position; TC: Citation count; ACP: Average citations per article; \(\geq\)100, \(\geq\)50: Numbers of articles with more than 100 or 50 citations, respectively; A1, A2: Numbers of articles published during the periods 1999–2008 and 2009–2018, respectively.  
\end{table} 
Table 5: Distribution of articles by publication source. One thousand nine hundred ninety-nine authors had contributed to the 451 studied articles. Thirty-three authors had more than five articles on the NLP-enhanced clinical trial research, while 87.44% of authors had participated in only one article. Table 8 depicts the top 19 ranked by H-index, where the top three were _[PERSON]_ (H-index as ten) from _the University of California, San Francisco, [PERSON]_ (H-index as eight) from the Foundation for _Research and Technology-Hellas_, and _[PERSON]_ (H-index as eight) from _Stanford University_. For the 19 listed authors, ten were from the USA, four from Spain, two from Germany, two from Greece, and one from the Netherlands. From the article count perspective, the top three were _[PERSON]_ (15 articles) from _Philips Research_, _[PERSON]_ (13 articles) from _Columbia University_, and _[PERSON]_ (13 articles) from the Foundation for _Research and Technology-Hellas_. From the ACP perspective, the top three were _[PERSON]_ (ACP as 84.58) from _the University of California, San Francisco, [PERSON]_ (ACP as 42.67) from _the University of California, San Francisco, and [PERSON]_ (ACP as 39.50) from _Saarland University_. It is worth noting that concerning the number of articles published during the period 1999-2008, _[PERSON]_ from _Stanford University_ ranked first with eight articles, while _[PERSON]_ from _Philips Research_ had the most articles published during the second period.