2.6 Assessment of risk of bias in the included trials
The Cochrane risk of bias tool was used to assess the risk of bias in the included studies. The tool contains six items addressing the possible different types of bias within clinical trials which include selection bias, performance bias, detection bias, attrition bias, reporting bias and other bias (22). The first domain of selection bias is divided into random sequence generation and allocation concealment (22). RevMan Web 5.3 software application (Review Manager Web. The Cochrane Collaboration, 2019) was used to plot the results of the risk of bias assessment (23). The judgments were of a low, high or unclear risk of bias for each study, regarding each domain.