Inappropriate comparisons of incidence and prevalence in epidemiologic research.

Several epidemiologists have published papers in major medical journals in which they compare incidence rates and prevalence and use these comparisons to support conclusions regarding questions of major public health importance. Although these papers have been criticized in published correspondence, we believe that continued use and advocacy of such comparisons by some epidemiologists has created the need for a full discussion of this practice. In this commentary, we review basic differences between incidence and prevalence and show that direct comparison of these two measures is inappropriate for conceptual, theoretical, and practical reasons.