Prevalence of depression over a 12-month period in a nonpatient population.

A nonpatient population of air traffic controllers, all of whom remained employed during the observation period, was examined monthly for one year for level of depression using the Zung Self-Rating Depression Scale. The average monthly prevalence of depression was 9.1%, with 7.0% at the symptom level, 1.9% at a level comparable to outpatients, and 0.2% with moderately severe levels. These figures were generally similar to those for other reported population groups, although exact comparisons were difficult because of the preselection for health in this population. Two patterns of depression were observed. One was characterized by an acute, episodic symptomatology returning to nonsymptomatic levels for most of the year, similar to Research Diagnostic Criteria (RDC) category "episodic minor depressive disorder." The other showed a chronic, fluctuating course with significant depressive symptomatology over half the year, similar to RDC category "chronic and intermittent minor depressive disorder."