Validation of the Thai World Health Organization Quality of Life-OLD (WHOQOL-OLD) among Thai older adults: Rasch analysis

Rasch analysis was employed to investigate the psychometric properties of the Thai version of the World Health Organization Quality of Life-OLD (WHOQOL-OLD) instrument among the Thai older adults. The analysis was conducted on a subset of 300 individuals randomly selected from a group of 800 older adults. The results revealed that the WHOQOL-OLD showed an acceptable fit to the Rasch model (χ²[9] = 7.39, p = 0.60), confirming unidimensionality, local independence, and satisfactory reliability (person separation index [PSI] = 0.75) when the domains were merged into three superitems: 1) autonomy, past-present-future activities, and death and dying; 2) social participation and intimacy; and 3) sensory ability. These three-domain superitems showed significant differential item functioning (DIF) related to education level (p < 0.05), which was resolved by splitting the items based on education level. Each WHOQOL-OLD domain also met the expectations, which included item-trait interaction fit, unidimensionality, local independence, lack of significant DIF, and satisfactory reliability. Ordinal-to-interval conversion tables were generated for the three-domain superitems by education level and for each WHOQOL-OLD domain. Therefore, the Thai WHOQOL-OLD and its domain are valid and reliable for the assessment of health-related quality of life (HRQoL) in between-group analyses among the Thai older population.