Study selection:
Decisions to select retrieved studies for further assessment are based on eligibility criteria. To minimize the chance of including non-relevant studies, two independent, trained researchers (AK and KA) went through the abstracts of every article and excluded the ones they seem unfit the decision to obtain and assess the full text was on whether one reviewer judged the article as fit for our study.
Subsequently, reviewers (AK, KA) conducted a full text review for all studies that passed the abstract screening. In case of conflict a third senior reviewer (MR) was asked to review the articles in question and decide, independent on what previous researchers decided upon. Two investigators used a standardized spreadsheet, based on the inclusion and exclusion criteria, in order to select studies to be included in the review. Reviewers were trained, and the spreadsheet was piloted prior to abstract screening.