Search strategy and selection of studies
We searched MEDLINE, Embase and CENTRAL from inception until 2019. We used a search strategy that combined MeSH terms for MEDLINE/Emtree terms for Embase and free text words. The search strings are available in Appendix S1. We used EndNote web to eliminate duplicates. Two authors (LC and LDM) independently assessed eligibility by screening study records by titles and abstracts, and the full-text manuscripts for final inclusion using Rayyan (Qatar Computing Research Institute, Doha, Qatar). In case of discrepancy, conflicts were resolved by discussion, and if not possible by arbitration with one of two senior authors (JB, JDP). In case of overlapping study populations, the largest and most complete dataset was included.