The odds ratio is in some cases (e.g. in case-control studies) a relevant measure in itself, but in other cases (e.g. cohort studies) it is used as an approximation of the relative risk of exposure to a studied factor. The approximation to relative risk is good when the baseline risk is low, but otherwise, two similar odds ratios can have different clinical interpretations (and two different odds ratios the same) because:

RR = OR/(1-R+OR*R)

where R = baseline risk, RR = relative risk, and OR = odds ratio. The clinical significance of a treatment effect cannot always be evaluated if the studied effect is presented as an odds ratio. The problem can be avoided by using a statistical method that provides direct estimates of the relative risk.