Q1 = Were the two groups similar and recruited from the same population?, Q2 = Were the exposures measured similarly to assign people to both exposed and unexposed groups?, Q3 = Was the exposure measured in a valid and reliable way?, Q4 = Were confounding factors identified?, Q5 = Were strategies to deal with confounding factors stated?, Q6 = Were the groups/participants free of the outcome at the start of the study (or at the moment of exposure)?, Q7 = Were the outcomes measured in a valid and reliable way?, Q8 = Was the follow up time reported and sufficient to be long enough for outcomes to occur?, Q9 = Was follow up complete, and if not, were the reasons to loss to follow up described and explored?, Q10 = Were strategies to address incomplete follow up utilized?, Q11 = Was appropriate statistical analysis used?, Y = Yes, N = No, U = Unclear.