Cross-cultural adaptation and psychometric properties of the Kessler Distress Scale (K10): an application of the rating scale model

The Hidden Toll of Psychological Distress in Australian Adults and Its Impact on Health-Related Quality of Life Measured as Health State Utilities

BACKGROUND

Psychological distress (PD) is a major health problem that affects all aspects of health-related quality of life including physical, mental and social health, leading to a substantial human and economic burden. Studies have revealed a concerning rise in the prevalence of PD and various mental health conditions among Australians, particularly in female individuals. There is a scarcity of studies that estimate health state utilities (HSUs), which reflect the overall health-related quality of life in individuals with PD. No such studies have been conducted in Australia thus far.

OBJECTIVE

We aimed to evaluate the age-specific, sex-specific and PD category-specific HSUs (disutilities) in Australian adults with PD to inform healthcare decision making in the management of PD.

METHODS

Data on age, sex, SF-36/SF6D responses, Kessler psychological distress (K10) scale scores and other characteristics of N = 15,139 participants (n = 8149 female individuals) aged >15 years were derived from the latest wave (21) of the nationally representative Household, Income and Labor Dynamics in Australia survey. Participants were grouped into the severity categories of no (K10 score: 10-19), mild (K10: 20-24), moderate (K10: 25-29) and severe PD (K10: 30-50). Both crude and adjusted HSUs were calculated from participants' SF-36 profiles, considering potential confounders such as smoking, marital status, remoteness, education and income levels. The calculations were based on the SF-6D algorithm and aligned with Australian population norms. Additionally, the HSUs were stratified by age, sex and PD categories. Disutilities of PD, representing the mean difference between HSUs of people with PD and those without, were also calculated for each group.

RESULTS

The average age of individuals was 46.130 years (46% male), and 31% experienced PD in the last 4 weeks. Overall, individuals with PD had significantly lower mean HSUs than those likely to be no PD, 0.637 (95% confidence interval [CI] 0.636, 0.640) vs 0.776 (95% CI 0.775, 0.777) i.e. disutility: -0.139 [95% CI -0.139, -0.138]). Mean disutilities of -0.108 (95% CI -0.110, -0.104), -0.140 (95% CI -0.142, -0.138), and -0.188 (95% CI -0.190, -0.187) were observed for mild PD, moderate PD and severe PD, respectively. Disutilities of PD also differed by age and sex groups. For instance, female individuals had up to 0.049 points lower mean HSUs than male individuals across the three classifications of PD. There was a clear decline in health-related quality of life with increasing age, demonstrated by lower mean HSUs in older population age groups, that ranged from 0.818 (95% CI 0.817, 0.818) for the 15-24 years age group with no PD to 0.496 (95% CI 0.491, 0.500) for the 65+ years age group with severe PD). Across all ages and genders, respondents were more likely to report issues in certain dimensions, notably vitality, and these responses did not uniformly align with ageing.

CONCLUSIONS

The burden of PD in Australia is substantial, with a significant impact on female individuals and older individuals. Implementing age-specific and sex-specific healthcare interventions to address PD among Australian adults may greatly alleviate this burden. The PD state-specific HSUs calculated in our study can serve as valuable inputs for future health economic evaluations of PD in Australia and similar populations.

General population normative data from seven European countries for the K10 and K6 scales for psychological distress

The 10-item Kessler Psychological Distress scale (K10) and its 6-item short-form version (K6) measure psychological distress, particularly anxiety or depressive symptoms. While these questionnaire scales are widely used in various settings and populations, general population normative data are rarely available. To facilitate the interpretation of K10 and K6 scores, we provide normative general population data from seven European countries. We used an online survey to collect K10 data from general population samples in Austria, Italy, Germany, France, the Netherlands, Poland and Spain. We calculated the age- and sex-specific normative values separately for each country. For more specific estimates of K10 and K6 scores for individuals or groups, we also established a multivariable regression model based on socio-demographic and health data. In total, N = 7,087 adults participated in our study (51.6% women; mean age, 49.6 years). The mean K10 score in the total sample was 8.5 points (standard deviation, 7.3) on 0-40 points metric, with mean scores in individual countries ranging from 6.9 (the Netherlands) to 9.9 (Spain). Women showed higher scores than men and younger participants scored higher than older participants. Our study is the first to present normative K10 and K6 data from several European countries using a consistent sampling approach. These reference values will facilitate the interpretation of K10 and K6 scores in clinical research and practice and also highlight the variation in psychological distress levels across countries and groups according to their socio-demographic and health characteristics.

Measuring distress in older population: Rasch analysis of the Kessler Psychological Distress Scale

OBJECTIVES

The 10-item Kessler Psychological Distress Scale (K-10) is a widely applied distress measure; however, its psychometric properties were not established with older populations using advanced methodology. The aim of this study was to examine psychometric properties of the K-10 through application of Rasch methodology and if possible, develop an ordinal-to-interval conversion to improve its reliability in older populations.

METHOD

The Partial Credit Rasch Model was applied to analyse K-10 scores of the sample including 490 participants (56.3 % females) aged 70 to 90 years and without dementia from the Sydney Memory and Ageing Study (MAS).

RESULTS

The initial analysis of the K-10 showed poor reliability and significant deviation from the expectations of the Rasch model. The best model fit was evident after correcting disordered thresholds and creating two testlet models to address local dependency between items (χ²(35) = 29.87, p = 0.71). The modified K-10 demonstrated strict unidimensionality, enhanced reliability and scale invariance across personal factors, such as sex, age, and education and permitted development of ordinal-to-interval transformation algorithms.

LIMITATIONS

Ordinal-to-interval conversion can only be applied for older adults with complete data.

CONCLUSIONS

The K-10 satisfied principles of fundamental measurement defined by Rasch model after minor modifications. Clinicians and researchers can transform K-10 raw scores into interval-level data using converging algorithms published here without altering the original scale response format, which increases reliability of the K-10.

Post-treatment Outcomes and Changes in Health Literacy of People Discharged from Specialist Substance Use Disorder Treatment Services

Health literacy comprises an individual’s ability to adequately access, understand and utilise health information, enabling effective navigation of the healthcare system. Low health literacy is a problem for people living with substance use disorders (SUDs). This study aims to examine whether health literacy changes for people discharged from specialist SUD treatment services. Two hundred thirty-one people recruited from residential SUD treatment services across New South Wales, Australia, completed a questionnaire upon entry into the service and again at 6 months post-treatment. Treatment outcomes were also measured. Three health literacy profiles were identified: lowest (n = 52, 22.5%), moderate (n = 111, 48.1%) and highest health literacy (n = 68, 29.4%). Lowest and moderate profiles showed improved health literacy at 6 months. However, the lowest profile still had significantly lower health literacy, quality of life and higher levels of psychological distress compared with participants in the highest profile at 6 months. People within the lowest health literacy profile improved, although they continued to experience lower health literacy and some poorer treatment outcomes. Health literacy interventions tailored for people within lowest health literacy profiles should be implemented and assessed for effectiveness within specialist SUD treatment services.

Psychometric properties and factor structure of the Kessler-10 among Ethiopian adults

BACKGROUND

Many common mental disorders are underdiagnosed and undertreated in low-resource countries. The ten-item Kessler Psychological Distress Scale (K10) is a brief screening tool widely used to assess psychological distress. We evaluated the K10's performance in an Ethiopian population by assessing internal consistency and construct validity through factor structure.

METHODS

K10 survey responses and sociodemographic data were collected from 1928 adults, including patients and caregivers from a general medical setting, who served as controls of a large epidemiological study.

RESULTS

The K10 had good internal consistency, with a Cronbach's alpha of 0.83. Results from exploratory factor analyses showed that the K10 had a two-factor solution that accounted for approximately 66% of the variance. Confirmatory factor analyses demonstrated that a unidimensional model with correlated errors, informed by a theoretical model, was the best fitting model for the setting (comparative fit index of 0.90 and root mean square error of approximation of 0.10).

LIMITATIONS

We did not assess the K10's test-retest reliability or its criterion validity (i.e., agreement with a reference measure).

CONCLUSIONS

Based on internal consistency and construct validity, the K10 can effectively assess psychological distress among Ethiopian adults for population-based research and potentially clinical screening, consistent with previous findings in this setting. Further studies are needed to test its criterion validity against a reference measure of psychological distress.