Comparing Subjective Well-being Longitudinally: Measurement Invariance of the Personal Wellbeing Index Across Time

The Personal Wellbeing Index (PWI) is commonly used as an instrument for measuring subjective well-being, and longitudinal comparisons of PWI scores are increasingly being used to monitor well-being trends within a nation. The aim of this study was to assess the longitudinal invariance of the PWI, as well as the latent mean differences across time, provided that scalar invariance was established. Using data from a sample of Chinese adults (N = 774), we conducted longitudinal confirmatory factor analysis to explore the measurement invariance of the PWI across a three-year period (with one assessment per year). We utilized a four-step approach (configural, metric, scalar, and residual) to evaluate the levels of invariance. The results indicated that the PWI demonstrated full scalar invariance and partial residual invariance over time, with noninvariant residual variances observed for Item 1 and Item 5. In addition, the latent factor means were significantly different between time points, with PWI scores showing an increase over time. Overall, our study provides empirical evidence that the PWI has satisfactory psychometric properties for longitudinal invariance, which allows for cross-time comparisons of subjective well-being. These findings have important implications for using the PWI as a tool to assess progress within a nation and evaluate the effectiveness of policies aimed at enhancing subjective well-being.