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

Abstract

Background: The distributional pattern of total scores on depression screening scales in the general population has not been well studied. Recent studies suggest that the total scores on depression screening scales follow an exponential pattern, with the exception of the lower end of the distribution. To further investigate the findings, we determined the distributions of the total and individual item scores on the Kessler Screening Scale for Psychological Distress (K6). Methods: Data were obtained from the National Survey of Midlife Development in the United States. Participants comprised 6,223 individuals between the ages of 25 and 74. The distributions of the total and individual item scores in various combinations were investigated with histograms and regression analysis. Results: Irrespective of the combination of items, the total and individual item scores followed an exponential pattern except at the lower scores. The estimated rate parameters of regression analysis were similar among distributions with the same number of chosen items. At the lower scores, the distributional patterns of total scores varied according to the ratio of "a little" to "none" for each item response. Conclusions: The present results have the potential to estimate the distribution of depressive symptoms in the general population. While the degree of depressive symptoms varies from individual to individual, an entire population may show a certain mathematical distribution.

Distribution of psychological distress is stable in recent decades and follows an exponential pattern in the US population

“…In contrast, the total scores with a low probability for the negative adverb option exhibited lower scores. Indeed, according to our calculations, the average probabilities of “none of the time” for 1997 and 2017 (74.1% and 74.0%, respectively) were higher than that of the National Survey of Midlife Development in the United States data (61.8%), which exhibited an exponential pattern for the whole distribution 41 . Our recent simulation using an ordinal scale model revealed that when the severity of psychological distress followed an exponential distribution, the total scores of a psychological distress scale exhibited an exponential pattern, except at the lower end of the distribution 42 .…”

Distributional patterns of item responses and total scores on the PHQ-9 in the general population: data from the National Health and Nutrition Examination Survey

“…These findings are consistent with results of other nationally representative surveys that the K6, CIS-R, and CES-D in the USA, England, and Japan, respectively [ 15 , 17 , 18 ]. Previous research demonstrated that the response rate of the negative adverb option (“not at all”) plays an important role in predicting the non-exponential pattern at the lower end of the distribution [ 13 , 33 ]. Specifically, at the lower end of the distribution, the sum of the item scores with a high rate for the negative adverb option showed higher scores in comparison with those expected from the exponential pattern.…”

Item Response Patterns on the Patient Health Questionnaire-8 in a Nationally Representative Sample of US Adults

“…To our knowledge, there is no evidence that the latent variable of depressive symptom scores in the general population follows a normal distribution. Given that the pattern of item responses has repeatedly shown a non-normal distribution, the normal distribution model of depressive symptom scores could require reconsideration ( 27 ).…”