Background: The tevel of overlapping of trials and systematic reviews (SRs) between LILACS and PubMed is uncertain.
Objectives: To analyse the level of overlapping of trials and SRs published in the last 10 years in LILACS and PubMed.
Methods: We performed a search in January 2017 on PubMed and LILACS to identify SRs and trials published between 2006 and 2015. Later years were excluded due to incomplete indexation.
The search terms in both databases were selected in order to favour their comparability (Box 1). We analysed trends of SRs and trials through a regression analysis performed in Stata® 14.1.
Results: In the last 10 years, excluding duplications, both databases presented a statistically significant upward trend of SRs and trial publications: +2225 yearly (IC95% 2104 to 2946; p< 0.0001) +1751 yearly (IC95% 1069 to 2433; p< 0.0001) respectively.
The search retrieved 530 494 unique trials in both databases, 1578 of which were indexed in both databases (overlapping of 0.30%); and 146 578 unique SRs, 1278 of them in both databases (overlapping of 0.87%) (Table 1).
The overlapping was 49.47% and 26.32% of trials and SRs identified considering only in LILACS respectively, and 0.30% and 0.89% only in PubMed. There are 176 and 550 LILACS journals, not indexed in PubMed, reporting trials and SRs respectively.
There was a statistically significant downward trend in the proportion of SRS indexed only in LILACS, despite a statistically significant increase in the absolute number of SRs (Fig.1a); and there was no important change in the trend of trial indexing (Fig.1b).
Conclusions: There is a low level of overlapping between LILACS and PubMed. Although the absolute number of studies published in LILACS is much lower than PubMed, there are still a non-marginal number of trials and SRs outside PubMed deserving attention. The number of trials seems stable over time but SRs are growing.