Do acupuncture trials have lower risk of bias over the last five decades? A methodological study of 4 715 randomized controlled trials

Objective To evaluate the change of the risk of bias (RoB) of acupuncture randomized controlled trials (RCTs) in the past five decades. Methods Multiple databases were searched. We included RCTs identified from systematic reviews (SRs) on acupuncture. General characteristics and RoB judgment for each domain were extracted. The proportions of RCTs at high and unclear RoB were calculated and the changes were examined by the Mann-Kendall test. Results We included 368 SRs including 4 715 RCTs. The rates of RCTs at unclear RoB were the highest in allocation concealment (63%), and at the lowest in incomplete outcome data (35%); in the last five decades, statistically significant reductions were found for random sequence generation (P< 0.001) and selective reporting (P= 0.01), and increases for blinding of participants and personnel (P< 0.001), blinding of outcome assessment (P< 0.001) and incomplete outcome data (P= 0.04). For the proportions of RCTs at high RoB, blinding of participants and personnel (47%) and blinding of outcome assessment (35%) were the poorest domains; there were no significant differences in changes for all domains. Conclusions Although improvements concerning unclear risk were observed for random sequence generation and selective reporting, major issues remain for allocation concealment and blinding. It is imperative to use valid randomization, specify how it is conducted, and try to test for selection bias and the success of masking by using the Berger Exner test.