3.4 Risk of bias among the studies reported on PEs
The results of the risk of bias evaluation was shown in Figure 2a and the summary of the risk of bias expressed in percentage were shown in Figure 2b. In general, about 75% of the reported studies on PEs scored only low risk to moderate risk. Only 25% of the reviewed studies on PEs showed high risk of bias. The different domains of the risk of bias reported among the individual studies were shown in Figure 2a.