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


METHODS
Data 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.


RESULTS
The 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.


CONCLUSIONS
The distributional pattern of the sum of the item scores could be predicted from the item responses of such items.
Department of Mental Health, Panasonic Health Center, Tokyo, Japan.|Department of Drug Evaluation and Informatics, Graduate School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
Shinichiro
http://orcid.org/0000-0002-7161-6967
S
Tomitaka
Department of Drug Evaluation and Informatics, Graduate School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
Yohei
Y
Kawasaki
Department of Drug Evaluation and Informatics, Graduate School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
Kazuki
K
Ide
Department of Drug Evaluation and Informatics, Graduate School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
Maiko
M
Akutagawa
Department of Drug Evaluation and Informatics, Graduate School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
Hiroshi
H
Yamada
Department of Health Promotion and Human Behavior, Kyoto University Graduate School of Medicine/School of Public Health, Kyoto, Japan.
Toshiaki A
TA
Furukawa
Center for the Development of Cognitive Behavior Therapy Training, Tokyo, Japan.
Yutaka
Y
Ono
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003863:Depression / Q000453:epidemiology* / Q000523:psychology*; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011569:Psychiatric Status Rating Scales; D011594:Psychometrics; D055815:Young Adult