THE MISUSE OF ATTRIBUTABLE AND PREVENTED FRACTIONS IN THE EVALUATION OF SCREENING IN CASE-CONTROL STUDIES

Methodological problems of evaluating screening programs in case-contr ol studies have been the subjects of controversial discussion in recen t years. The increasing number of published papers presenting results of case-control studies on the evaluation of cancer screening during t he last few years demonstrate that this design has rapidly gained popu larity in cancer epidemiology, although the methodological criticism h as not been solved yet arid is usually not reflected in the interpreta tion of the study results. A new development in this area has been the incorporation into the evaluation of some measure of the population i mpact of screening programs. This paper discusses the application of t hese measures (attributable and prevented fractions) to screening situ ations. The implicit assumptions required for their valid interpretati on are delineated. Primarily, it is our intention to raise the flag of caution against the naive practical application and overoptimistic in terpretation of attributable and prevented fraction estimates derived from case-control studies on the evaluation of screening.