Mplus Users Guide v6.. - Muthén & Muthén

CHAPTER 14MODEL COMMAND IN MULTIPLE GROUPANALYSISIn multiple group analysis, two variations of the MODEL command areused. They are MODEL and MODEL followed by a label. MODEL isused to describe the overall analysis model. MODEL followed by alabel is used to describe differences between the overall analysis modeland the analysis model for each group. These are referred to as groupspecificmodels. The labels are defined using the GROUPING option ofthe VARIABLE command for individual data in a single file, by theFILE options of the DATA command for individual data in separatefiles, and by the program for summary data and Monte Carlo simulationstudies. It is not necessary to describe the full model for each group inthe group-specific models. Group-specific models should contain onlydifferences from the model described in the overall MODEL commandand the model for that group.Following is an example of an overall MODEL command for multiplegroup analysis:MODEL: f1 BY y1 y2 y3;f2 BY y4 y5 y6;In the above overall MODEL command, the two BY statements specifythat f1 is measured by y1, y2, and y3, and f2 is measured by y4, y5, andy6. The metric of the factors is set automatically by the program byfixing the first factor loading in each BY statement to 1. The interceptsof the factor indicators and the other factor loadings are held equalacross the groups as the default. The residual variances are estimated foreach group and the residual covariances are fixed at zero as the default.Factor variances and the factor covariance are estimated for each group.Following is a group-specific MODEL command that relaxes theequality constraints on the factor loadings in a two-group analysis:MODEL g2: f1 BY y2 y3;f2 BY y5 y6;In the above group-specific MODEL command, the equality constraintson the factor loadings of y2, y3, y5, and y6 are relaxed by includingthem in a group-specific MODEL command. The first factor indicator424