Factor structure of Zung self-rating depression scale for workers.

The Zung self-rating depression scale (SDS) was applied to workers of a railway company. A total of 1,784 night-shift workers responded to the questionnaire and 1,394 daytime workers were set as the control group. The average age of the subjects was 39.9. The SDS index decreased with age. A factor analysis was conducted and two factors were obtained having an initial eigen value over 2.0. Factor 1 was the group of 8 positive items, accounting for 18.2%. Factor 2 was the group of 8 depressive items, accounting for 18.1%. Four items including "loss of weight," "constipation," "good appetite," and "partner coping" did not construct a distinct factor. The factor structure of SDS items of the night-shift workers was similar to those of the control group.