2.5. Study quality:
Given that trial inclusion with a high risk of bias may distort the outcomes of a meta-analysis (26, 27), the Cochrane Collaboration tool was used for evaluating the risk of bias. The following items were evaluated: randomization sequence generation; allocation concealment; blinding of participants, personnel, investigator, and assessor; attrition rates; and companies financial interest. These items were given high, unclear, or low risk of bias rating. A study was categorized as having low, medium, or high-risk according to the key areas of allocation concealment, reporting of attrition rates, and participants and assessor (high = all 4 factors rated high, medium = 2 or 3 factors rated high or unclear, and low = all key areas rated low).