Figure 1.

Path diagrams representing the structural models used in this study. Factors are represented by circles, items by squares, and causal pathways by arrows. Unidimensional model: all items load on one single factor that accounts for their covariance. Correlated-traits model: item subsets load on separate factors that are correlated; accounts for between-item multidimensionality. Bifactor model: each item loads on 2 uncorrelated factors; one general for all items and one specific for item subgroups; accommodates within-item multidimensionality. Two-tier model: a bifactor model with multiple general factors, which can be correlated.