TABLE 2.

Risk of bias questions answered as part of level of evidence rating.

Type of bias	Questions	Applicable articles
Selection bias	Was administered dose or exposure level adequately randomized?	Experimental animal, human controlled trial
	Was allocation to study groups adequately concealed?	Experimental animal, human controlled trial
	Were the comparison groups appropriate?	Cohort, case control, cross-sectional
Confounding bias	Did the study design or analysis account for important confounding and modifying variables?	All
Performance bias	Were experimental conditions identical across study groups?	Experimental animal
	Were the research personnel and human subjects blinded to the study group during the study?	Experimental animal, human controlled trial
Attrition/exclusion bias	Were outcome data complete without attrition or exclusion from analysis?	Experimental animal, human controlled trial, cohort, case control, cross-sectional
Detection bias	Can we be confident in the exposure characterization?	All
	Can we be confident in the outcome assessment?	All
Selective reporting bias Other bias	Were all measured outcomes reported?	All
	Were there no other potential threats to internal validity (e.g., statistical methods were appropriate)?	All

Note: Questions from OHAT handbook (20).