Table 2.

Cochrane Collaboration tool to assess risk of bias for randomized controlled trials

Authors, year	Risk of bias within each domain							Overall risk of bias across studies
	Selection bias Random sequence generation	Selection bias Allocation concealment	Reporting bias Selective reporting	Other bias Other sources of bias	Performance bias Blinding (participants and personnel)	Detection bias Blinding (outcome assessment)	Attrition bias Incomplete outcome data
Cottingham et al, 198830	Unclear	Unclear	Unclear	High	High	High	Low	High
Levine et al, 199729	Unclear	Unclear	Unclear	High	High	Unclear	High

Judgement: Bias is assessed as a judgment (high, low, or unclear) for individual elements from five domains (selection, performance, attrition, reporting, and other).

Assessment of risk of bias (version 5.1.0):

(Within a study) Low risk of bias: Low risk of bias for all key domains

Unclear risk of bias: Unclear risk of bias for one or more key domains

High risk of bias: High risk of bias for one or more key domains

(Across studies) Low risk of bias: Most information is from studies at low risk of bias

Unclear risk of bias: Most information is from studies at low or unclear risk of bias

High risk of bias: The proportion of information from studies at high risk of bias is sufficient to affect the interpretation of results