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Friday, October 23, 2015

Why is the prevalence of major depression not changing?

The availability of estimates of major depression prevalence (the proportion of population with a major depressive episode in the past year) from multiple Canadian surveys has made it possible to assess whether the prevalence of major depression is changing or not. The answer is "no" (click here for more details), or here. In a more recent study, we sought to determine why. Ahead of time, it was possible to say that there are several explanations due to the fact that prevalence, roughly speaking, is the incidence (rate of occurrence of new case) multiplied by the mean duration. With increasing treatment of depression, one might hope that episode incidence would decrease, since long-term use of antidepressants should reduce recurrence rates. Alternatively, treatment should shorten the duration of episodes. In this recent study, we looked at both things. But, neither one changed. Apparently, it is difficult to discern the effects of antidepressant medications on population health. Either the current efforts of the health system are failing to affect the burden of depression or other factors (e.g. increasing risk factors for depression) are at play that may have obscured this impact.