Background: The aging population increases rapidly across the world. Timely and effective screening of their mental-health problems is important to individuals, families, and the whole society. The Kessler-6 screening measure (K6) is a very popular instrument for non-specific psychological distress. However, few studies have focused on the psychometric properties of this instrument in the older population.
Methods: The present study employed Mokken scale analysis to evaluate its dimensionality and structure. This study also used differential item functioning (DIF) to examine whether the same structure existed across sex in a national representative sample of old Chinese people. Data were drawn from a public data set, the 2010 China Family Panel Studies (CFPS2010), and responses from a total of 6450 participants aged 60 years old and above (3136 males and 3314 females) were included in the final analysis.
Results: Mokken scale analysis supported the unidimensional structure of the K6. Differential item functioning (DIF) analysis revealed that two of the six items ("Hopeless" and "Everything was an effort") were marked for DIF based on the Chi-square. However, their impacts were negligible in terms of McFadden's pseudo R2.
Conclusions: The K6 demonstrates adequate psychometric properties in the old Chinese population. The sum of all six items can be used as an indicator of non-specific psychological distress. Differences in the indicator across sex should be considered as a real difference in psychological distress between the female and the male.
Keywords: Differential item functioning; Dimensionality; Mokken scale analysis; Psychological distress; Sex differences.