Interpreting and evaluating the CASP-19 quality of life measure in older people.

ABSTRACT

OBJECTIVE: to investigate how to interpret changes on the CASP-19 quality of life scale for older people, and whether it discriminates between, and is responsive to, relevant differences or changes in participants' circumstances. METHODS: analysis of data from the English Longitudinal Study of Ageing for those completing CASP-19 in both Wave 1 and Wave 2 (n = 6,482). Cross-sectional and longitudinal comparisons, using multiple linear regression, of CASP-19 scores with respect to eight anchor variables. RESULTS: cross-sectional comparisons found differences in mean CASP-19 scores at Wave 1 between categories of anchor variables varied from 1.9 for living alone to 8.0 for being able to walk ¼ mile with difficulty. Longitudinal comparisons of changes in CASP-19 found that subjects that had moved between categories of the anchor variables over 28 months, had changed their mean CASP-19 score by about 1 unit in the expected direction, compared with the unchanged category. These changes were statistically significant for six of the eight anchors. CONCLUSIONS: the cross-sectional comparisons help interpret differences and indicate CASP-19 has discriminatory power. The longitudinal changes show that CASP-19 is responsive to changes in most anchor variables that reflect some aspects of quality of life.