Table 2: Cochrane risk of bias of included randomized controlled trials.

First author [ref]
(Year)
Hollifield [18]
(2007)
Zhang [25] (2010) Zhang [26](2010)Zhang [27]
(2011)

(1) Random sequence generation
(selection bias)
L
(computerized randomization)
L
(computerized randomization)
UU
(2) Allocation concealment
(selection bias)
L
(central allocation)
L
(sequentially numbered, opaque sealed envelopes)
UU
(3) Blinding of participants
(performance bias)
HHHH
(4) Blinding of outcome assessment
(detection bias)
L
(mentioned)
L
(mentioned)
UU
(5) Incomplete outcome data
(attrition bias)
L
(mentioned)
UUU
(6) Selective reporting
(reporting bias)
UUUU
(7) Other sources of bias
(other bias)
UUUU

L: low risk of bias; H: high risk of bias; U: unclear.