Background: The purpose of the present study was to examine the measurement properties of positive affect items among the Japanese population.
Methods: Responses to the Japanese version of the Center for Epidemiologic Studies Depression Scale and four additional negatively revised items of the original positive affect items were compared for 85 Japanese psychiatric out-patients with dysphoric-mood-related symptoms and 255 demographically matched controls.
Results: Responses to positive affect items were generally comparable between the two groups, whereas responses to negative symptom items were markedly different (P < 0.002 for all comparisons). The group difference was most marked for symptom persistence. Responses to the four negatively revised items of positive affect revealed a similar picture to that of the negative symptom items. The internal consistency of the scale significantly improved when the original positive affect items were replaced by the negatively revised items (P < 0.001 for both).
Conclusions: Positive affect items with positive wording cannot be used to assess depressive disorders in the Japanese population adequately, but this can be done with the corresponding negatively revised items.