Risk and prognosis.

Epidemiology is concerned with the study of the frequency of disease occurrence. Clinical epidemiology is that part of epidemiology that deals with questions concerning clinical practice. Risk and prognosis are important concepts in clinical research and patient management . Risk of disease can be viewed as the chance, or the probability, that disease occurs. In order to know the probability of disease or death, one has to know the frequency of occurrence of disease. For the study of risk and prognosis the frequency of new disease events (incidence), and not the frequency of existing disease (prevalence) is of importance. This is because it is possible to estimate the probability of disease and thereby the risk of disease by estimating its incidence. The risk of disease can be measured in two ways: directly from the cumulative incidence, with or without use of the life table, and indirectly from the incidence rate.