Psychometric properties of the International Wellbeing Index in community-dwelling older adults

Background: This is the first study to analyze the psychometric properties of the International Wellbeing Index (IWI), which comprises the Personal Wellbeing Index (PWI) and National Wellbeing Index (NWI), among community-dwelling older adults. Methods: The IWI was applied to 1106 community-dwelling adults aged 60 years and over. The sample was additionally assessed using scales for comorbidity, disability, mood, general orientation to life, social support, health-related quality of life, and two questions assessing satisfaction with life as a whole and with life in Spain. The PWI and NWI were separately analyzed for acceptability, internal consistency, convergent and discriminative validity, and precision. Linear regression analyses of the PWI and the NWI were also conducted. Results: Mean scores were 71.0 +/- 13.5 for the PWI and 49.5 +/- 14.4 for the NWI. No floor or ceiling effects were detected. Cronbach's alpha was 0.88 for the PWI and 0.92 for the NWI. Factor analysis identified two factors in the IWI, and one factor in the PWI and NWI respectively. The PWI showed a correlation of 0.50 with the "satisfaction with life as a whole" item, and the NWI showed a correlation of 0.73 with the "satisfaction with life in Spain" item. There were significant differences in scores: in the PWI, according to gender, age, social support, education and depression; and in the NWI, according to education and depression. The regression model identified psychosocial, health and functional factors as determinants of the PWI (explained variance: 46.8%). Conclusions: The IWI displays good acceptability and is a consistent, valid and precise measure of global quality of life in older adults.