Chapters 11 and 12 have reviewed several measures of risk and of excess risk. The relative risk and the odds ratio are important as measures of the strength of the association, which is an important consideration in deriving a causal inference. The attributable risk is a measure of how much of the disease risk is attributable to a certain exposure. Consequently, the attributable risk is useful in answering the question of how much disease can be prevented if we have an effective means of eliminating the exposure in question. Thus, the relative risk is valuable in etiologic studies of disease, whereas the attributable risk has major applications in clinical practice and public health.