A longitudinal assessment of the responsiveness of the ICECAP-A in a randomised controlled trial of a knee pain intervention
The ICECAP-A is a simple measure of capability well-being for use with the adult population. The descriptive system is made up of five key attributes: Stability, Attachment, Autonomy, Achievement and Enjoyment. Studies have begun to assess the psychometric properties of the measure, including the construct and content validity and feasibility for use. This is the first study to use longitudinal data to assess the responsiveness of the measure. This responsiveness study was completed alongside a randomised controlled trial comparing three physiotherapy-led exercise interventions for older adults with knee pain attributable to osteoarthritis. Anchor-based methodologies were used to explore the relationship between change over time in ICECAP-A score (the target measure) and change over time in another measure (the anchor). Analyses were completed using the non-value-weighted and value-weighted ICECAP-A scores. The EQ-5D-3L was used as a comparator measure to contextualise change in the ICECAP-A. Effect sizes, standardised response means and t tests were used to quantify responsiveness. Small changes in the ICECAP-A scores were seen in response to underlying changes in patients’ health-related quality of life, anxiety and depression. Non-weighted scores were slightly more responsive than value-weighted scores. ICECAP-A change was of comparable size to change in the EQ-5D-3L reference measure. This first analysis of the responsiveness using longitudinal data provides some positive evidence for the responsiveness of the ICECAP-A measure. There is a need for further research in those with low health and capability, and experiencing larger underlying changes in quality of life.