Wellbeing in New Zealand: a reliability and validity study of the New Zealand Sovereign Wellbeing Index
Background Measurement tools that evaluate personal, social and occupational life domain wellbeing are increasingly being used to measure how people are feeling and flourishing. The New Zealand Sovereign Wellbeing Index (NZSWI) is a measure specifically developed to evaluate the wellbeing of New Zealanders, and to track how their wellbeing is changing over time. Best practice in psychometric measurement requires sound assessment in order to be useful for those interpreting and utilising the results of wellbeing measures, and the NZSWI’s reliability and validity has yet to have been investigated. The aim of this research was to determine the test-retest reliability, internal consistency, and construct validity of the NZSWI.
Methods The aim of this research was to determine the test-retest reliability, internal consistency, and construct validity of the New Zealand Sovereign Wellbeing Index. Seventy-one adults aged 18 years and over completed a survey battery, including the New Zealand Sovereign Wellbeing Index and additional validated wellbeing measures at two time points, one week apart. Test-retest reliability between the two time points was analysed by calculating an intraclass correlation coefficient. Internal consistency was assessed at time point 1 using a Cronbach’s alpha correlation coefficient. Construct validity, both convergent and discriminant, was evaluated against validated psychometric tools using Spearman’s rank correlation coefficient.
Results With regard to test-retest reliability, 78 items (89%) displayed substantial reliability (Cronbach’s coefficients between 0.61 and 1.0). Ten items (11%) had moderate reliability (coefficients between 0.41 and 0.60). For internal consistency, five of the twenty total topic headings (25%) had coefficient alphas above 0.70, eleven (55%) had coefficient alphas between 0.50 and 0.69, two (10%) had alphas between 0.40 and 0.49, and two (10%) had coefficient alphas under 0.25. With regard to convergent validity, all items measured within the 15 topic tables displayed strong validity with Spearman’s coefficients above 0.50. For discriminant validity, one topic (11%) returned a small correlation, six topics (67%) returned medium correlations, and 3 two topics (22%) returned strong correlations, therefore demonstrating variable validity in this aspect.
Conclusion On the whole these results suggest that the New Zealand Sovereign Wellbeing Index is a reliable and valid psychometric measurement tool for assessing wellbeing constructs in a New Zealand adult population.