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Abstract
Treatments for depression have improved, and their availability has markedly increased
since the 1980s. Mysteriously the general population prevalence of depression has
not decreased. This "treatment-prevalence paradox" (TPP) raises fundamental questions
about the diagnosis and treatment of depression. We propose and evaluate seven explanations
for the TPP. First, two explanations assume that improved and more widely available
treatments have reduced prevalence, but that the reduction has been offset by an increase
in: 1) misdiagnosing distress as depression, yielding more "false positive" diagnoses;
or 2) an actual increase in depression incidence. Second, the remaining five explanations
assume prevalence has not decreased, but suggest that: 3) treatments are less efficacious
and 4) less enduring than the literature suggests; 5) trial efficacy doesn't generalize
to real-world settings; 6) population-level treatment impact differs for chronic-recurrent
versus non-recurrent cases; and 7) treatments have some iatrogenic consequences. Any
of these seven explanations could undermine treatment impact on prevalence, thereby
helping to explain the TPP. Our analysis reveals that there is little evidence that
incidence or prevalence have increased as a result of error or fact (Explanations
1 and 2), and strong evidence that (a) the published literature overestimates short-
and long-term treatment efficacy, (b) treatments are considerably less effective as
deployed in "real world" settings, and (c) treatment impact differs substantially
for chronic-recurrent cases relative to non-recurrent cases. Collectively, these a-c
explanations likely account for most of the TPP. Lastly, little research exists on
iatrogenic effects of current treatments (Explanation 7), but further exploration
is critical.