It is an important tool for our understanding of medicine and health but like any tool it must be properly used. Cigarette smokers die from lung cancer much more often than non-smokers, and more people die in hospitals than anywhere else. Nearly all unbiased researchers feet that cigarette smoking causes lung cancer deaths based to a large extent on the statistical evidence. However, few believe that the increased probability of dying in a hospital suggests that hospitals cause death. The increased risk of dying in a hospital is because the best treatment for most life threatening illnesses is only available in hospitals.
Risk is the likelihood of some outcome occurring given the presence of some factor.
The outcome is generally referred to as a disease although it might also be death or some adverse medical condition. The factor whose relationship with the outcome we are interested in is generally referred to as the exposure. In the health sciences, the measure of risk we are usually interested in is the Relative Risk, although other measures of risk such as an Odds Ratio might be dictated by the nature of the study. Research using a case control design is the most common use of an odds ratio. This calculation requires that information regarding the exposed population is available.