Review criteria
We searched MEDLINE, EMBASE, Epistemonikos and the Cochrane Central Register of Controlled Trials from inception to April 2020. Pairs of reviewers independently screened all identified records with titles, abstracts and full texts using EndNote and Covidence software. We reported the number of eligible studies according to design, sample size, methodological quality / risk of bias, and proportions and measures of association for primary outcomes for each low value practice.