The Psychometric Properties of the Kessler Psychological Distress Scale (K6) in an Epidemiological Sample of Canadian Youth

Objective: This study (1) describes the distribution of Kessler Psychological Distress Scale (K6) scores in an epidemiological sample of youth, (2) reports its item correlations and internal consistency reliability, (3) tests for measurement invariance by age (youth vs. adults) and sex, and (4) examines its predictive power for past-year psychiatric disorders. Method: Youth aged 15 to 19 years (n = 2010) and adults aged 20 to 64 years (n = 2010) from the Canadian Community Health Survey-Mental Health who completed the K6 were included. Past-year psychiatric disorders were measured using the World Health Organization Composite International Diagnostic Interview 3.0 (WHO-CIDI). Polychoric correlation matrices and ordinal reliability coefficients were calculated to assess internal consistency of the K6, and confirmatory factor analysis was used to test for measurement invariance. Area under the curves (AUCs) were computed to determine the extent to which the K6 predicted a positive screen on the WHO-CIDI. Results: K6 scores showed a J-shaped distribution, with >50% of youth having scores <= 3. Item and total scores were higher for females versus males. Item correlations were robust (0.31-0.78) and internal consistency was high (alpha = 0.86). Full measurement invariance was demonstrated between youth and adults, as well as between male and female youth. The K6 was a strong predictor of major depressive episode (AUC = 0.848), generalized anxiety disorder (AUC = 0.847), and bipolar disorder (AUC = 0.853). Conclusions: The K6 is a valid and reliable measure of psychological distress among youth. Its brevity and robust predictive power for psychiatric disorder confirm its utility in clinical and community settings to identify youth needing comprehensive psychiatric assessment.