Do reasons for major depression act as causes?

We make sense of human behavior using reasons, which produce understanding via a subjective empathy-based first-person perspective and causes, which leads to explanations utilizing objective facts about the world assessed scientifically. We evaluate the common sense hypothesis that for episodes of major depression (MD), reasons act as causes. That is, individuals who have highly understandable depressive episodes will have, on average, fewer objective scientifically validated causes than those who have un-understandable episodes. The understandability of a MD as defined by the Diagnostic and Statistical Manual, 4th Edition (DSM IV) experienced in the past year in 630 personally interviewed twins from a population-based registry was rated, with high reliability, from rich contextual information. We predicted, from these understandability ratings, via linear and logistic regression, 12 validated risk factors for MD reflecting genetic and long-term environmental liability. No significant association was observed between 11 of these indices and the understandability of the depressive episode. The only significant finding-higher cotwin risk for MD associated with greater understandability-was opposite that predicted by the reasons-as-causes hypothesis. Our results do not support the hypothesis that reasons for MD act as causes. These findings, unlikely to result from low power, may be explicable from an empirical and/or philosophical perspective. Our results are, however, consistent with 'the trap of meaning' hypothesis, which suggests that understanding does not equal explanation and that while reasons may be critical to help us empathize with our patients, they are unreliable indices of objective risk factors for illness.