Study quality
As regards it has been adopted that study inclusion with a high risk of
bias can distort the meta-analysis outcomes
(25, 27),
the Cochrane Collaboration tool was used for evaluating the bias risk.
The included studies quality were evaluated by following items:
randomization sequence generation; allocation concealment; participants,
personnel, assessor and investigator blinding; financial interest by
companies and attrition rates. These items were given a rating of high,
low, or unclear risk of bias. A randomized controlled trial (RCT) was
categorized as having overall high, low or medium risk based on the
basic items of allocation concealment, participants and assessor
blinding , and reporting of attrition rates (High = High risk of bias
for one or more than one key areas, Low = Low risk of bias for all key
areas, and Medium = Unclear or low risk of bias for all key areas).