Background: Previous studies have shown that item responses and total scores on depression screening scales follow characteristic distribution patterns in the United States and Japanese general populations. However, the degree to which these findings, especially in terms of item responses, can be generalized to a European population is unknown. Thus, we analyzed the item responses and total score distribution for the Center for Epidemiologic Studies Depression Scale (CES-D) in a representative Irish cohort from a large, recent study-the Irish Longitudinal Study on Ageing (TILDA).
Methods: We used CES-D data from the 2009-2011 TILDA (8504 individuals). Responses for the 16 depressive symptoms included "rarely," "some of the time," "occasionally," and "all of the time." Item response patterns and total score distribution across these 16 depressive symptom items were examined using graphical analyses and exponential regression modeling.
Results: Lines for item responses followed the same pattern across the 16 items. These lines were characterized by intersections in the vicinity of a single point between "rarely" and "some of the time" and parallel patterns from "some of the time" to "all of the time" on a log-normal scale. Total scores for the 16 items exhibited an exponential pattern, except for at the lower end of the distribution.
Conclusions: The present findings suggest that item responses and total scores on depression screening scales among the general population follow the same characteristic patterns across populations from multiple nations.