Background: There is steady growth in systematic reviews (SRs) in PubMed but trends for other study types are not well known.
Objectives: To analyse the trends in absolute and relative numbers of SRs, RCTs, reviews and case reports, out of all published studies in the last 10 years in LILACS and PubMed.
Methods: We performed a search in January 2017 on PubMed and LILACS, to identify SRs, trials, non-SRs ('Reviews') and case reports published between 2006 and 2015. Due to incomplete indexation of studies we excluded the years 2016 and 2017 from the analysis. The search methods by study type are described in Box 1. The choice of these methods was based on common search terms in both databases to favour the comparability of proportions. We analysed trends of each study type through a regression analysis performed in Stata® 14.1.
Results: In the last 10 years, there was a similar, statistically significant upward trend publication of SRs, both in LILACS and PubMed (Fig. 1a, 1b). There was no change in the trend of publication of RCTs in LILACS (Fig. 2a) but there was a statistically-significant decrease in the proportion of RCTs published in PubMed, despite opposite results in the absolute number of trials (Fig. 2b). There was a statistically significant downward trend in Reviews in LILACS (Fig. 3a) but no important change in the proportion trend in PubMed, despite a statistically significant increase in the absolute number of Reviews (Fig. 3b). There was a statistically significant downward trend in Case Reports proportion in LILACS (Fig. 4a) but without statistical significance in absolute numbers. There was a statistically significant decrease trend in Case Reports proportion trend in PubMed (Fig. 4a) despite a non-statistically-significant increase in absolute numbers (Fig. 4b).
Conclusions: SRs publication is steadily growing, both in LILACS and PubMed. The trend patterns are different for other study designs and differ in absolute and relative trends between both databases.