Psychometric Properties of the Persian Kessler Psychological Distress Scale (K10) among Iranian Older Adults

BACKGROUND: We measured the psychometric properties i.e., validity, reliability, and stability of the Persian 10-item Kessler Psychological Distress Scale (K10) among older adults in Iran. METHODS: We recruited elderly (60+ years) subjects (20 per-item of the questionnaire) from various sampling units in the general population of Gorgan district, Golestan. After translation/back-translation process, the questionnaire underwent various forms of validity and reliability, including Cronbach alpha (overall, by items, and by group of yes to an item and no to an item). Intra-class correlation coefficient (ICC) was measured with two weeks interval, and inter-rater agreement was also determined. Both exploratory and confirmatory factor analysis were also conducted, along with receiver-operator characteristic vis-à-vis hospital anxiety and depression scale.  RESULTS: In total, 190 subjects (47.3% males, mean age: 70.3, 95% CI 69.2-71.4) participated. A total of 35.8% had PD (i.e. score >20). Alpha coefficient was 0.88 with no item had this below 0.86. The alpha coefficients to report a yes to an item (a = 0.85) or no to an item (a = 0.90) was similar to each other. ICC for test-retest at two weeks’ interval was 0.90. EFA showed one-factor structure of the underlying construct, with a cumulative variance of 97.1%. CFA showed high fit indices for the questionnaire (0.91) and low standardized residual of 0.05. CONCLUSION: We measured psychometric parameters of the Persian version of the K10 scale for detecting PD among older adults, which was found to be adequately valid, reliable, and stable. Our questionnaire fills the prior gaps regarding the lack of validated tools for timely detection and management of PD among older adults in the Persian-language cultural contexts. Our study emphasizes that Kessler questionnaire is a unidimensional scale, and detects non-specific PD with all items indicating a single underlying construct of “distress”.