Cohort studies† Vallone, 48 2004 Miller and Phillips, 47 2009 Miller et al, 34 2012 Miller et al, 49 2016
 1. Clear focused issue?YesYesNoYes
 2. Cohort recruitment acceptable?CDYesCDNo
 3. Exposure accurately measured?NoCDNoCD
 4. Outcome accurately measured?NoNoNoNo
 5a. Confounders identified?NoNoCDYes
 5b. Confounders considered appropriately?NoNoNoYes
 6a. Follow-up complete enough?CDNoCDCD
 6b. Follow-up long enough?CDYesYesCD
 9. Results believable?NoNoCDYes
 10. Results applicable?NoNoCDNo
 11. Results consistent with others?CDNACDYes
Quality assessment Low Low Low Mod