Exploratory factor analysis and Rasch analysis to assess the structural validity of the Adult Social Care Outcomes Toolkit Proxy version (ASCOT-Proxy) completed by care home staff

Purpose: Rasch analysis and exploratory factor analysis (EFA) were used to evaluate the structural validity of the ASCOT-Proxy measures completed by staff on behalf of older adults resident in care homes, by comparison to the ASCOT-SCT4, the measure of social care-related quality of life (SCRQoL) from which the ASCOT-Proxy was developed. Methods: EFA was conducted on the ASCOT-SCT4 and the two ASCOT-Proxy measures (Proxy-Proxy, Proxy-Resident), to determine if they retained the single factor of the original ASCOT-SCT4 measure found in samples of older community-dwelling adults. Rasch analysis was also applied to measures with a single factor structure in the EFA. Results: ASCOT-Proxy-Resident had a single factor structure, as did the original ASCOT-SCT4 (also, found in this analysis when completed by care home staff). The ASCOT-Proxy-Proxy had a two factor structure. Rasch analysis of ASCOT-Proxy-Resident and ASCOT-SCT4 had an acceptable model fit, internal consistency and met the assumptions of unidimensionality and local independence. There was evidence of less than optimal distinguishability at some thresholds between responses, and low frequency of rating of the ‘high level needs’. Conclusion: The ASCOT-Proxy-Resident is a valid instrument of SCRQoL for older adults resident in care homes, completed by staff proxies. Due to the two-factor structure, which differs from the original ASCOT-SCT4, we do not recommend the use of the ASCOT-Proxy-Proxy measure, although collecting data as part of the ASCOT-Proxy questionnaire may support its feasibility and acceptability. Further qualitative study of how care home staff complete and perceive the ASCOT-Proxy is encouraged for future studies.