Table 2: Quality assessment of included randomized controlled trials.

Study IDSequence generationAllocation concealmentIncomplete outcome dataBlindingOther source of biasSelective outcome reportingRisk of bias

Liang 2000 [15]UnclearUnclearNoUnclearUnclearNoUnclear
Tan et al. 2003 [10]Table of random numberUnclearYesUnclearUnclearNoUnclear
Wu et al. 2007 [17]UnclearUnclearNoUnclearUnclearNoUnclear
Yan and Li 2010 [13]UnclearUnclearYesUnclearUnclearYesUnclear
Yang et al. 2003 [12]UnclearUnclearNoUnclearUnclearNoUnclear
Zeng and Feng 2003 [11]UnclearUnclearNoUnclearUnclearNoUnclear
Yu and Liao 1999 [16]UnclearUnclearYesUnclearUnclearNoUnclear