Measures of Association

Measures of Association

Incidence rates can be used to calculate two types of effects. One is the attributable risk, or the absolute effect. The attributable risk is the difference between two incidence rates. This is most commonly used in comparing rates of exposed with nonexposed populations. The second type of effect is the relative risk, which is the ratio of the incidence rates of the exposed and unexposed groups. In case–control studies, it is not possible to estimate in-cidence rates. Relative risks, however, can be calculated with an odds ratio, which is the ratio of the odds of exposure of the case patients to that of the control subjects.