Trends in WHOQOL-BREF and EUROHIS-QOL-8 health-related quality of life scores among the Thai population from the 1990s to 2023: an application of Rasch analysis

The World Health Organization Quality of Life-brief (WHOQOL-BREF) and the EUROHIS-QOL-8, an abridged version of WHOQOL-BREF, tools have been used widely in Thailand to assess health-related quality of life (HRQoL) in the general population. The availability of data spanning multiple time points now presents an opportunity to explore long-term trends in HRQoL scores and examine whether Thai respondents’ interpretations of questionnaire items have changed over time. Therefore, the primary objective of this study was to examine long-term trends of WHOQOL-BREF scores collected at three time points. Analyses of differential item functioning (DIF) were also performed to investigate whether Thai individuals interpreted and endorsed WHOQOL-BREF domains/items and EUROHIS-QOL-8 items consistently across time to support the validity of these comparisons. This study conducted Rasch analysis on small, randomly selected Bangkok-only subsamples ( n = 150 per time point) from three datasets ( n = 300 in 1990s, n = 1200 in pre-COVID 2019, and n = 2000 in post-COVID 2023) using the WHOQOL-BREF and EUROHIS-QOL-8 instruments. DIF explored temporal changes in item interpretation across age, sex, and dataset. Mean HRQOL scores derived from four WHOQOL-BREF domains and EUROHIS-QOL-8 increased across the three time points; however, social and environmental domains did not show any statistically significant difference ( p > 0.05). DIF revealed that physical and psychological domains were more difficult to score high for the samples from the 1990s compared to those from the two time periods, whereas social and environmental domains displayed an opposite effect. Although these findings highlight the increasing HRQoL trends in Bangkok and suggest the importance of considering societal changes when interpreting long-term HRQoL data, an investigation with a nationally representative sample of Thai population is warranted for future studies to confirm these findings.