Everyone feels depressed or "a bit low" from time to time, so those seeking the incidence (rate of new cases) or prevalence of depression need a good definition. Most such studies, including the multicenter one from Dr. Ronald C. Kessler and colleagues that is currently listed at #15 (JAMA, 280[23]:3095-105, 2003; latest citation count 38, total cites 117), use the 1994 edition of the American Psychiatric Association’s diagnostic criteria, the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, or DSM-IV. In this large study, of over 9,000 people, the interviews were conducted by trained lay people.

The lifetime prevalence of major depressive disorder was found to be 16.2%, which translates into almost 34 million U.S. adults, and for the 12 months up to the interview the figure was 6.6%. A decade earlier, in 1990-92, the lifetime figure had been 14.9%. A similar survey in six European countries revealed a lifetime history of mood disorder in 14% of the 21,425 interviewees (J. Alonso, et al., Acta Psychiatr. Scand. Suppl., 109[Suppl. 420]: 21-27, 2004). A fairly consistent picture seems to be emerging, at least for the northern hemisphere.

When Science Watch contacted Dr. Kessler at the Harvard Medical School’s Department of Health Care Policy, Boston, he noted that depression was now beginning to attract attention, and for two main reasons. The availability of new drug treatments had meant that more people were seeking treatment, while the World Health Organization had recognized depression as the "single most burdensome disease in the world among people in the early and middle years of life." However, he added, the most widely cited finding from the paper had been the disturbing finding that only 21.7% of those with major depressive disorder in the previous 12 months were being adequately treated, a figure arrived at by multiplying the proportion of people on any treatment at all (just over half) by the proportion of that treatment that was deemed adequate.

21.7% is a worryingly low figure, and one that has prompted the Georgia Health Care Leadership Council and the Midwest Business Group on Health to set up a project looking at cost-effectiveness from the employer’s perspective. The idea, Dr. Kessler tells Science Watch, is to develop guidelines that "can be used to help motivate employers to invest in high-quality depression treatment and to hold providers accountable for delivering high-quality depression treatment." If successful, these guidelines could be used as a model nationwide.