Literature search and study characteristics
The electronic search resulted in 8,546 articles of which 3,031 in MEDLINE, 2,029 in Embase and 3,086 in the Cochrane Library. We removed 3,620 duplicates, leaving 4,926 articles to be screened by title and abstract. 4,803 studies were excluded for the reasons displayed in Figure 1. This left 123 articles that were eligible for full-text analysis. During that process, another 82 articles were excluded for the reasons displayed in the supplement (table S1). As a result, there were 41 studies of which 25 had data that were not compatible with our methodology for quantitative analysis (Supplement, table S2). Most of these studies were comparing mean scores, making it impossible to extract or extrapolate ORs and quantitatively synthesize the findings. These studies were used at a later stage during the qualitative interpretation. Quantitative synthesis was therefore made, based on the remaining 16 articles (Supplement, table S3).