Prognostic knowledge: interest and methods.

The value of prognostic information and some of the statistical aspects of prognostic studies are discussed. In the first part, seven areas of medical activity where knowledge of prognostic factors is used are identified: prediction of disease evolution, treatment decisions, design and analysis of clinical trials, comparison of non-randomized series of patients, assessment of additional clinical examinations and laboratory tests, understanding of the physio-pathology of disease, screening. In the second part, the nature of the data collected in prognostic studies is discussed, and a few statistical methods useful for the identification of prognostic factors are outlined. The paper concludes with an example of a prognostic study in Chronic Lymphocytic Leukemia.