The use of conditional probabilities to examine age-period-cohort data: further evidence for a period effect in major depressive disorder.

There is growing evidence that rates of major depression have been increasing over this century, with successive birth cohorts showing increased lifetime risks and earlier ages of onset. In this paper, we describe and compare onset rates in six birth cohorts of first degree relatives of probands with affective disorders from the NIMH Collaborative Study, using graphs of conditional probabilities of first onset. There is evidence of a period effect and age-period interaction for both men and women.