Relationship between Item Responses of Negative Affect Items and the Distribution of the Sum of the Item Scores in the General Population

Abstract

BackgroundSeveral studies have shown that total depressive symptom scores in the general population approximate an exponential pattern, except for the lower end of the distribution. The Center for Epidemiologic Studies Depression Scale (CES-D) consists of 20 items, each of which may take on four scores: “rarely,” “some,” “occasionally,” and “most of the time.” Recently, we reported that the item responses for 16 negative affect items commonly exhibit exponential patterns, except for the level of “rarely,” leading us to hypothesize that the item responses at the level of “rarely” may be related to the non-exponential pattern typical of the lower end of the distribution. To verify this hypothesis, we investigated how the item responses contribute to the distribution of the sum of the item scores.MethodsData collected from 21,040 subjects who had completed the CES-D questionnaire as part of a Japanese national survey were analyzed. To assess the item responses of negative affect items, we used a parameter r, which denotes the ratio of “rarely” to “some” in each item response. The distributions of the sum of negative affect items in various combinations were analyzed using log-normal scales and curve fitting.ResultsThe sum of the item scores approximated an exponential pattern regardless of the combination of items, whereas, at the lower end of the distributions, there was a clear divergence between the actual data and the predicted exponential pattern. At the lower end of the distributions, the sum of the item scores with high values of r exhibited higher scores compared to those predicted from the exponential pattern, whereas the sum of the item scores with low values of r exhibited lower scores compared to those predicted.ConclusionsThe distributional pattern of the sum of the item scores could be predicted from the item responses of such items.

Characteristic distribution of the total and individual item scores on the Kessler Screening Scale for Psychological Distress (K6) in US adults

“…These results concur with previous findings using the CES-D [20], suggesting that regardless of the depression screening scales, the sum of item scores approximate an exponential pattern, with the exception of the lowest scores. A theory proposed by our research group may explain why the sum of item scores for depression screening scales follow an exponential pattern [11,24,25].…”

“…The estimated parameters increased in proportion to the number of chosen items, and the distributions of the same number of items showed similar parameters, consistent with previous reports using the CES-D [20].…”

“…As the previous study demonstrated, the ratio of "a little" to "none" contributes to the distributional pattern at the lower end of the distribution [20]. According to the previous study, while the total scores of items with high values of the ratio of "a little" to "none" are expected to exhibit lower frequencies than predicted from the exponential regression curve, the total scores of items with low values of the ratio of "a little" to "none" are expected to exhibit higher frequencies than predicted from the regression curve.…”

“…According to the previous study, while the total scores of items with high values of the ratio of "a little" to "none" are expected to exhibit lower frequencies than predicted from the exponential regression curve, the total scores of items with low values of the ratio of "a little" to "none" are expected to exhibit higher frequencies than predicted from the regression curve. On the other hand, the ratios of "some" to "a little" were similar among all 6 items [20]. Therefore, the ratios of "a little" to "none," and "some" to "a little" were calculated for all 6 items.…”

“…Thus, in our previous studies, we analyzed the distributions of the total scores of the chosen items on the CES-D in various combinations and found that for any combination of items, the total scores of the selected items approximated an exponential pattern, with the exception of the lowest scores [20]. Furthermore, we observed that (1) the total score distributions with the same number of chosen items exhibited similar estimated rate parameters; (2) the estimated rate parameters increased in proportion to the number of chosen items; and (3) the ratio of "none" to "some" of item responses contributed to the non-exponential pattern of total score distributions at the lowest scores [20]. These findings suggest that the distributional patterns of the total scores are dependent on the item responses of such items.…”