# Prerequisite for conversion from odds ratio to relative risk to be valid

as question, since we can do the conversion from odds ratio (p1/q1)/(p2/q2) to relative risk (p1/(p1+q1))/(p2/(p2+q2)) fairly easily, I wonder if there is anything that I need to pay attention before doing this?

It is obvious that if I am doing a case-control study, I shouldn't do a conversion, because I never know the relative risk from this kind of study, but anything other things that I need to consider?

Thanks.

• Odds ratio versus relative risk offers a good summary of those two measures. Another caveat that is frequently seen is people that apply a logistic regression model, but interpret the results with RR instead of OR. – chl Jan 28 '11 at 9:05