Table 3.

Cohort Studies, Risk of Bias Analysis (n = 7).

Assessment	Were two groups similar and from same population?	Were exposures measured similarly?	Was exposure measured in a valid way?	Were confounding factors identified?	Were confounding factors dealt with?	Were outcomes measured in a valid way?	Was follow-up complete?	Was appropriate statistical analysis used?
Yes	7	7	7	6	6	7	7	7
No	0	0	0	1	0	0	0	0
Not applicable	0	0	0	0	1	0	0	0