Fig. 3From: Changing trends in clinical research literature on PubMed database from 1991 to 2020Composition change trend of each research type in clinical research literature in PubMed database from 1991 to 2020. A Trend change of primary literature proportion; B trend change of secondary literature proportion. RCT: randomized clinical trial; PCT: pragmatic clinical trial; Sys-meta: systematic review and meta-analysisBack to article page