A high-quality systematic review (SR) should be based on a comprehensive literature search. Cochrane methodology review: failure to identify trials reported in conference proceedings and other grey literature might affect the results of a systematic review. But it is unclear currently how many meta-analyses of surgery have searched grey literature, and whether is it helpful.
We aimed to analyze whether searching grey literature is helpful or not for meta-analyses (MAs) of surgery.
We selected robotic surgical MAs as the sample to investigate the question. Systematically, we searched PubMed, Embase, the Cochrane Library, Web of Science and China Biology Medicine disc from 2015 to 2017 using search terms “robotic-assisted surgery, laparoscopic, open surgery” etc. We mainly analyzed the grey literature search and the included studies.
Among the 91 MAs included, 38 (41.8%) reported that grey literature was searched, but only one included grey literature. For this study, the results were the same whether grey literature was included or excluded. Why grey literature was excluded was not explained in remaining 37 studies.
Comprehensive literature retrieval is emphasized highly, but most studies in surgery do not carry this out. The reason why grey literature is excluded may that it was low quality, but each study should explain this clearly.