Severe and nonsevere events in first onsets versus recurrences of depression: evidence for stress sensitization.

Overall, research has evidenced support for Post's (1992) model, which asserts that the 1st episode of depression is more likely to be associated with severe life events than are subsequent episodes. In spite of this, there are significant gaps in the understanding of the stress-depression association. This study aimed to address three gaps by (a) identifying the explanatory model underlying the association (stress sensitization vs. stress autonomy), (b) elucidating how the role of stress changes with successive episodes, and (c) examining the role of nonsevere events. The impact and occurrence of severe and nonsevere events in a 5-year longitudinal study of late-adolescent women were examined using Cox regression models. Overall, we found support for the stress sensitization model over the stress autonomy model. Specifically, the impact of nonsevere (but not severe) events was greater in individuals with a history of depression compared with those with no history of depression. In addition, the occurrence of severe (but not nonsevere) events was greater for 1st onsets than recurrences. These effects were modified by event independence. The results were discussed in terms of the underlying mechanisms of the stress-depression association and future directions for research were elaborated.