3.

'Risk of bias' summary: review authors' judgements about each risk of bias item for each included study: blank cells for randomised controlled trials (Barennes 2005; Slama 1990) indicate that the particular outcome was not measured in the study); blank cells for non‐randomised controlled trials (Chlup 2009 and Gunning 1978) indicate that overall low risk of bias was established according to the ROBINS‐I (risk of bias in non‐randomised studies of interventions, see Appendix 4).