Figure 2.

(a) Risk of bias graph: review authors’ judgments about each risk of bias item presented as percentages across all included studies. Note that an item was rated “+” (ie, low risk of bias) only when the measure taken to prevent certain risk of bias was clearly stated in the paper; when evidence/quotes or explanation were not available in the text or after clarifying with the authors of the included studies, a rating of “?” (ie, unclear risk of bias) was given and (b) review authors’ judgments about each risk of bias item for each included study. Note that “other bias” was defined as other sources of risk on top of selection, performance, detection, attrition, and reporting biases. Specifically, carry-over effects in cross-over trials and baseline imbalance between groups were considered as “other bias.”