Measurement Invariance Across Age Groups and Over 20 Years' Time of the Negative and Positive Affect Scale (NAPAS)

The factor structure and measurement invariance across gender of Mroczek's and Kolarz's scales of positive affect (PA) and negative affect (NA) have been examined in past studies: however, little is known about the measurement invariance across age groups and over time, which are important psychometric properties for developmental research. The current study sought to fill this gap using the data from the National Survey of Midlife Development in the United States (MIDUS). Multi-group confirmatory factor analysis (CFA) was used to examine increasing levels of measurement invariance across gender and age groups. Longitudinal CFA was also used to test measurement invariance over three time points using the data from MIDUS 1 (N = 3,748), MIDUS 2 (N = 2,257), and MIDUS 3 (N = 1,414). Results supported full scalar invariance across gender, age groups, and over time. The latent means for NA were significantly different between men and women at time 1 and 2, but not at time 3: the latent means for both PA and NA were also different across age groups. There were no significant differences for PA and only trivial differences for NA over time within individuals. Implications of these results for longitudinal research are discussed.