Find a peer reviewed research article with a results section. report on: what came out significant? What was the p-value?, what was the x2? what was conclusion? Measurement invariance is a basic requirement for longitudinal modeling, which tests if individuals' scores at different waves are directly comparable (Vandenberg and Lance 2000). In this study, we were interested in comparing individuals' scores across time and across males and females. This requires the assumption of metric invariance (i.e., the same measurement model and relations between each indicator and the latent factor must hold across time and gender). We tested these assumptions by comparing the fit of sequentially restrictive models (Table 1). To reduce the number of indicators, items were combined randomly into four parcel for POS (composed by 2 items each), and into five parcels for PA (composed by four items each) at each time point. Item parcels are likely to increase the stability of the parameter estimates, to improve the variable to sample size ratio, and to reduce the effects of nonnormality (e.g., Little et al. 2002). All parcels were highly reliable (mean alpha = .88, SD = .07)