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.

**Answer**

In a sense, odds ratios are more universal than risk ratios so we spend too much time on risk ratios. Risk ratios are incapable of being constant over a wide range of risks, whereas an odds ratio is capable of being constant. For example, if a risk ratio is 3, the starting risk level cannot exceed 1/3. Because of this, models stated in terms of odds ratios often contain fewer interaction terms than models for relative risk (or for risk difference).

**Attribution***Source : Link , Question Author : lokheart , Answer Author : Frank Harrell*