3.3 Risk of bias evaluation
24 RCTs were evaluated for literature quality. Ten studies reported a generation of random sequences, one study was a random draw [20], six for random number table [15,16,18,21,23,34], two for randomized envelope [17,32], one for random sampling [33]. Of note, four studies [14,15,17,32] reported using the allocation concealment and one study [19] mentioned double-blinding, the risk of bias evaluation is summarized in (Fig. 2, 3)