Measurement invariance
To ensure meaningful comparison across time, longitudinal measurement invariance was estimated for civic engagement and mental health. For the civic engagement variables, scalar invariance was achieved for social conscience, while partial scalar invariance was attained for social engagement and civic action when the intercepts of two items measuring the former and four items measuring the latter were allowed to vary across time. Thus, it is possible to make a mean comparison for these two civic engagement measures, albeit it should be done with caution. As for the two dimensions of mental health, scalar invariance was achieved for both measures, allowing for meaningful comparisons across time (Longitudinal invariance models for civic engagement and mental health indicators.