Risk of Bias Assessment
As previously mentioned, the Cochrane Collaboration Risk of Bias Tool was used to assess validity of the citations included in the meta-analysis. Areas assessed included method of randomization and allocation concealment, blinding, and attrition rate. Figure 2summarizes the results of the risk of bias assessment.
Although all five studies were randomized controlled trials, only three (Cha, 2016; Konishi, 2008; Schulman, 2015) were clear in the method of randomization, while only one (Cha, 2016) was clear in the method of allocation concealment. Only one (Schulman, 2015) was able to blind participants and outcome assessors by having a placebo preparation. However, given that the main outcomes of interest in the meta-analysis are objective, dichotomous outcomes, the failure to blind would not seem to significantly affect the results. In effect, all the included studies were deemed to have low risk of bias in terms of blinding of outcome assessment. As for attrition bias and reporting bias, the majority (Akizawa, 2009; Konishi, 2008; Schulman, 2015) of the studies had low risk of bias.