Has 'lifetime prevalence' reached the end of its life? An examination of the concept.

Many cross-sectional surveys in psychiatric epidemiology report estimates of lifetime prevalence, and the results consistently show a declining trend with age for such disorders as depression and anxiety. In a closed cohort with no mortality, lifetime prevalence should increase or remain constant with age. For mortality to account for declining lifetime prevalence, mortality rates in those with a disorder must exceed those without a disorder by a sufficient extent that more cases would be removed from the prevalence pool than are added by new cases, and this is unlikely to occur across most of the age range. We argue that the decline in lifetime prevalence with age cannot be explained by period or cohort effects or be due to a survivor effect, and are likely due to a variety of other factors, such as study design, forgetting, or reframing. Further, because lifetime prevalence is insensitive to changes in treatment effectiveness or demand for services, it is a parameter that should be dropped from the lexicon of psychiatric epidemiology.