A measure of quality of life in early old age: the theory, development and properties of a needs satisfaction model (CASP-19)

Quality of life is the subject of much research. However it lacks an agreed theoretical basis. In studies with older populations (ill) health has been used as a proxy measure for quality of life (QoL). We have developed a needs satisfaction measure of QoL in early old age. Our measure has four ontologically grounded domains: control, autonomy, pleasure, and self-realization. The measure was piloted with focus groups, a self-completion pilot, and cognitive interview testing. This produced a 22-item scale that was included in a postal questionnaire and sent to 286 people aged 65-75 years. A 92% response rate was achieved. The scale was reduced to 19 items on the basis of statistical analysis. The domains have Cronbach's alphas between 0.6 and 0.8. Correlations between the four domains range from 0.4 to 0.7. A second order factor analysis revealed a single latent QoL factor. The scores for the 19-item scale are well distributed along the range although they exhibit a slight negative skew. Concurrent validity was assessed using the Life Satisfaction Index-well being. A strong and positive association was found between the two scales (r=0.6, p=0.01). The CASP-19 appears to be a useful scale for measuring QoL in older people.