Measuring what matters: evaluating the psychometric properties of goal attainment scaling in a psychosocial dementia trial

BACKGROUND: It can be challenging to identify clinically meaningful, responsive primary outcomes for psychosocial intervention trials in people with dementia. Goal Attainment Scaling (GAS), a personalised, patient-generated outcome measure, enables individuals to define and evaluate progress toward meaningful goals. Evidence regarding its psychometric properties in dementia trials, however, remains limited. OBJECTIVE: To evaluate the feasibility, reliability, and validity of GAS within the randomised controlled trial of NIDUS-Family (New Interventions in Dementia Study), a goal-based psychosocial intervention. METHODS: 302 people with dementia and family carer dyads collaboratively set baseline goals toward supporting the person with dementia to live well at home. In a psychometric evaluation guided by the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) framework, we examined follow-up completion (measuring feasibility); rater agreement; intra-rater reliability; construct validity by assessing correlations between change in GAS and quality-of-life (DEMQOL-proxy and CarerQoL); and predictive validity by testing whether GAS change predicted living at home at 12 months. RESULTS: GAS completion rates were 86% at 6 months and 82% at 12 months. GAS demonstrated excellent inter-rater (Intraclass Correlation Coefficient = 0.99) and intra-rater reliability (Cohen's kappa = 0.91). There were significant but weak positive correlations between GAS change and carer and person with dementia quality-of-life (r = 0.14-0.22). GAS change was associated with remaining at home (odds ratio 1.08 per point increase; P <.01). CONCLUSION: GAS is feasible, valid and reliable, so may be a sensitive and clinically meaningful candidate primary outcome for psychosocial dementia trials. Correlations with global quality of life were significant but modest, consistent with GAS capturing personalised rather than generic outcomes.