estimate the relative risk (see rare disease assumption). The validity of the odds ratio depends highly on the nature of the disease studied, on the sampling methodology and on the type of follow-up. Although in classical case–control studies, it remains true that the odds ratio can only approximate the relative risk in the case of rare diseases, there is a number of other types of studies (case–cohort, nested case–control, cohort studies) in which it was later shown that the odds ratio of exposure can be used to estimate the relative risk or the incidence rate ratio of exposure without the need for the rare disease assumption. When the logistic regression model is used to model the case–control data and the odds ratio is of interest, both the prospective and retrospective likelihood methods will lead to identical maximum likelihood estimations for covariate, except for the intercept. The usual methods of estimating more interpretable parameters than odds ratios -- such as risk ratios, levels, and differences -- is biased if applied to case–control data, but special statistical procedures provide easy to use consistent estimators. Impact on longevity and public health Tetlock and Gardner claimed that the contributions of medical science to increasing human longevity and public health were negligible, and too often negative, until Scottish physician Archie Cochrane was able to convince the medical establishment to adopt randomized control trials after World War II. See also Nested case–control study Retrospective cohort study Prospective cohort study Randomized controlled trial References Further reading (Still a very useful book, and a great place to start, but now a bit out of date.) External links Wellcome Trust Case Control Consortium Epidemiology Design of experiments Nursing research