Table 2: Quality assessment of the included randomized controlled trials.

Included trialsSequence generationAllocation concealmentBlinding of participants personnel and outcome assessorsIncomplet outcome dataSelective outcome reportingOther sources of biasRisk of bias

Cai 2004 [18]UnclearUnclearUnclearYesNoUnclearHigh
Zhang 2007 [19]UnclearUnclearUnclearYesNoUnclearHigh
Chen et al. 2008 [20]UnclearUnclearUnclearYesNoUnclearHigh
Zhang et al. 2004 [21]UnclearUnclearUnclearYesNoUnclearHigh
Zhou et al. 2003 [22]UnclearUnclearUnclearYesNoUnclearHigh
Hu et al. 1994 [23]UnclearUnclearUnclearYesNoUnclearHigh