Lifetime co-morbidity of panic attacks and major depression in a population-based study: age of onset.

We used survival analysis to test for a suspected effect of co-morbidity of DIS/DSM-III major depression and panic attack on the age of onset of each of these disorders, in a population-based sample from four sites of the National Institute of Mental Health (NIMH) Epidemiologic Catchment Area Program (N = 12668). The possible effects of gender and presence of a co-morbid disorder on age of onset of the single disorders were analysed using the Cox proportion-hazard-model, with gender as an explanatory variable and the co-morbid disorders as time-dependent covariates. The disorders begin earlier in life when they are co-morbid than when they occur singly. The occurrence of one disorder increases the chance of occurrence of the other. Females have from 1.7 to almost twice the risk for developing panic and/or depression compared with men, even if the co-morbid disorder precedes the index disorder or is lifetime co-morbid. These findings are compatible with a hypothesis of a higher severity in co-morbid cases when compared with a single disorder.