Table 1.

Cochrane Risk of Bias Tool and Descriptions

Bias Domain	Bias Source	Description	High Risk	Low Risk	Unclear Risk
Attrition	Incomplete outcome data	Described the completeness of outcome data for each main outcome, including attrition and exclusions from the analysis. Stated whether attrition and exclusions were reported, the numbers in each intervention group (compared with total randomized participants), reasons for attrition/exclusions where reported.	Attrition bias because of amount, nature or handling of incomplete outcome data	Handling of incomplete outcome data was complete and unlikely to have produced bias	Insufficient reporting of attrition/exclusions to permit judgment of “low risk” or “high risk” (eg, number randomized not stated, no reasons for missing data provided)
Detection	Blinding of outcome assessment	Described all measures used, if any, to blind outcome assessors from knowledge of which intervention a participant received. Provided any information relating to whether the intended blinding was effective.	Detection bias because of knowledge of the allocated interventions by outcome assessors.	Blinding was likely effective	Not described in sufficient detail
Performance	Blinding of participants and personnel	Described all measures used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. Provided any information relating to whether the intended blinding was effective	Performance bias because of knowledge of the allocated interventions by participants and personnel during the study.	Blinding was likely effective.	Not described in sufficient detail
Reporting	Selective reporting	Stated how the possibility of selective outcome reporting was examined by the authors and what was found.	Reporting bias because of selective outcome reporting.	Selective outcome reporting bias not detected	Insufficient information to permit judgment (it is likely that most studies will fall into this category)
Selection	Random sequence generation	Described the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it should produce comparable groups.	Selection bias (biased allocation to interventions) because of inadequate concealment of allocations before assignment.	Random sequence generation method should produce comparable groups	Not described in sufficient detail
	Allocation concealment	Described the method used to conceal the allocation sequence in sufficient detail to determine whether intervention allocations could have been foreseen in advance of, or during, enrollment.	Selection bias (biased allocation to interventions) because of inadequate concealment of allocations before assignment.	Intervention allocations likely could not have been foreseen in advance of, or during, enrollment	Not described in sufficient detail
Other	Any other bias, ideally prespecified	Any important concerns about bias not addressed above. If particular questions/entries were prespecified in the study's protocol, responses should be provided for each question/entry.	Bias because of complications not covered elsewhere in the table.	No other bias detected	There may be a risk of bias, but there is either insufficient information to assess whether an important risk of bias exists; or insufficient rationale or evidence that an identified complications will introduce bias.