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

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.