Effects of positive and negative life events on time to depression onset: an analysis of additivity and timing

While the relationship of life events to depression onset has occupied researchers for almost a quarter of a century, few studies have attempted to account for either the temporal patterning of events relative to episode onset, or, the effect of multiple events in a study period. In this report, we attempt to address the issues of timing of events, multiple events (both positive and negative) and multiple aspects (both positivity and negativity) of single events on latency time to depression onset, while simultaneously accounting for possible decay in the effects of events over time. We use the proportional hazards approach to model the effects of life events and consider modelling the change in impact of events with the passage of time. After interviewing 142 recurrent unipolar patients using the Life Events and Difficulties Schedule, we rated severity and positivity of life events reported during the 6-month period prior to onset. As we hypothesized, additional life events occurring after an initial provoking agent level event significantly alter the risk of illness onset. Additional severely threatening events decrease the time to onset, but positive events do not appear to delay onset. Interestingly, seemingly neutral events had a highly significant effect in shortening the time to onset. We note the many limitations imposed on the interpretation of these findings related to the selected group of subjects studied and encourage those who have more generalizable data to apply these methods of analysis.