Expanded User's Guide: Harm

Except for the exposure under study, were the compared groups similar to each other?

Were there clearly identified comparison groups that were similar with respect to important determinants of outcome, other than the one of interest?
RCT, cohort , case-control?
Other known prognosis factors similar or adjusted for?

Were the outcomes and exposures measured in the same way in the groups being compared?

Was follow-up sufficiently long and complete?

Is the temporal relationship correct?

Is there a dose-response gradient ?

How strong is the association between exposure and outcome?

How precise is the estimate of risk?

Are the results applicable to my patients?

What is the magnitude of the risk?

Should I attempt to stop the exposure?

Relative risk (RR) is the risk of the outcome in the exposed group divided by the risk of the outcome in the unexposed group:

RR = (a/a+b)/(c/c+d)
(Used for prospective cohort studies)

Odds ratio (OR) is the odds of a case patient being exposed divided by the odds of a control patient being exposed:

OR = (a/c)/(b/d) - ad/bc (Used for retrospective case-control studies)