## 4 Performance and Collaboration Analyses Results
### Analyses of Country/Region, Institution, and Author  
Forty-five countries/regions had contributed to the 451 articles. Twelve countries/regions had more than ten articles about the NLP-enhanced clinical trial research, while 14 countries/regions had contributed to only one article each. Table 6 depicts the top 20 ranked by H-index. The top four were the USA (42 H-index, 231 articles), Germany (17 H-index, 57 articles), the UK (16 H-index, 51 articles), and the Netherlands (14 H-index, 39 articles), which were also the top four ranked by article count. Figure 1: Analysis of trends in articles. The table also includes the citation count (TC), average citations per article (ACP), numbers of articles with more than 100 and 50 citations (\(\geq\)100, \(\geq\)50, respectively), and numbers of articles published during 1999-2008 (A1) and 2009-2018 (A2). The USA had the top rank position for almost all index metrics (except ACP index), reflecting the high quality of its articles, as well as its dominant position in the NLP techniques for clinical trial text processing research. In addition, the USA was the main collaborator for countries of Germany, the UK, Canada, Australia, and China. Germany was the main collaborator for the USA, the UK, the Netherlands, Spain, and Greece. There were 605 institutions that participated in the 451 studied articles. Thirty-five institutions had more than five articles on the NLP-enhanced clinical trial research, while 441 institutions had participated in only one article each. Table 7 shows the top 17 ranked by H-index, among which the top three were _Stanford University_, _the National Institutes of Health_, and _the University of California_, _San Francisco_. For the 17 listed institutions, eight were from the USA, three from the Netherlands, three from the UK, one from Germany, one from Greece, and one from Spain. From the article count perspective, the top three were _Stanford University_ (25 articles), _Columbia University_ (21 articles), and _the Technical University of Madrid_ (17 articles). From the ACP perspective, the top three were _the University of California_, _San Francisco_ (75.86 ACP), _National Institutes of Health_ (59.50 ACP), and _University of Oxford_ (39.67 ACP). It is worth noting that concerning the number of articles published during the period 1999-2008, _Stanford University_ was ranked first with 14 articles, while most of the articles of _Columbia University_ were published during the second period, demonstrating a flourishing development in the NLP-enhanced clinical trial research. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**C** & **H** & **A (R)** & **TC** & **ACP** & \(\geq\)**100** & \(\geq\)**50** & **A1** & **A2** & **Main collaborator (CT \(\geq\) 9)** \\ \hline the USA & 42 & 231 (1) & 6425 & 27.81 & 11 & 30 & 58 & 173 & the UK; Germany; China; Canada; Australia & Greece; Spain; the UK; the Netherlands; USA; Belgium & Greece; Spain; the UK; the Netherlands; USA; Belgium & UK; the Netherlands; USA; Belgium & UK; the Netherlands; Germany; the UK; Greece \\ the Netherlands & 14 & 39 (4) & 541 & 13.87 & 0 & 2 & 5 & 34 & Spain; Belgium; Germany; the UK; Greece \\ Canada & 12 & 17 (9) & 1164 & 68.47 & 1 & 6 & 6 & 11 & the USA \\ Australia & 10 & 19 (7) & 245 & 12.89 & 0 & 0 & 2 & 17 & the USA \\ Spain & 9 & 27 (5) & 423 & 15.67 & 0 & 3 & 4 & 23 & the Netherlands Germany; Greece; Belgium \\ France & 8 & 20 (6) & 366 & 18.30 & 0 & 3 & 4 & 16 & \\ China & 8 & 17 (9) & 286 & 16.82 & 0 & 2 & 1 & 16 & the USA \\ Greece & 8 & 19 (7) & 308 & 16.21 & 0 & 2 & 6 & 13 & Germany; Spain; the Netherlands \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Distribution of articles by country/region.