Derivation, and establishment of the validity and reliability, of the CASP-11-SG quality of life scale among community-dwelling older adults.

Purpose: The number and proportion of older adults, aged ≥ 60 years, in Singapore is rapidly increasing. A valid and reliable quality of life (QoL) measure will enable assessment of their situation and help evaluate social and clinical interventions, potentially improving care. This study aims to evaluate the validity and reliability of the control, autonomy, self-realization, and pleasure (CASP)-12v.3 QoL scale and establish a scale suitable for use among older adults in Singapore.

Methods: Data from 3526 community-dwelling older adults from a national survey was used. Measurement properties of the CASP-12v.3 scale were evaluated. Confirmatory factor analysis (CFA; testing single- and two-factor models with residual covariances for negatively worded items and a bifactor model) was performed in half of the sample and exploratory factor analysis (EFA) was performed in the other half. The results led to revised CFA models and the CASP-11-SG scale. The CASP-11-SG scale's measurement properties, convergent, and known-groups validity, and measurement equivalence/invariance (ME/I) across English and Chinese languages were evaluated.

Results: Item 3 'I feel free to plan for the future' of the CASP-12v.3 scale had low correlation with other items of the control/autonomy subscale, low item-total correlation and high item-scale correlation. While CFA and EFA supported the two-factor model, removing item 3 improved model fit. The resulting CASP-11-SG scale (Cronbach's alpha: 0.81) demonstrated convergent and known-groups validity and partial ME/I across English and Chinese languages.

Conclusion: The CASP-11-SG scale, with satisfactory psychometric properties, can be used for assessing QoL among older adults in Singapore.