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Example 25
Figure 25-1: Sörbom model for Olsson data
Specifying the Model
E Open Ex25.amw. If you performed a typical installation, the path will be
C:\Program Files\IBM\SPSS\Amos\21\Examples\<language>\Ex25.amw.
The path diagram is the same for the control and experimental groups and is shown in
Figure 25-1. Some regression weights are fixed at 1. The means of all the residual
(error) variable means are fixed at 0. These constraints will remain in effect throughout
the analysis.
Constraining the Latent Variable Means and Intercepts
The model in Figure 25-1, Sörbom’s model for Olsson data, is unidentified and will
remain unidentified for every set of cross-group constraints that Amos automatically
generates. For every set of cross-group constraints, the mean of pre_verbal and the
intercept in the equation for predicting post_verbal will be unidentified. In order to
allow the model to be identified for at least some cross-group constraints, it is
necessary to pick one group, such as the control group, and fix the pre_verbal mean
and the post_verbal intercept to a constant, such as 0.
E In the List of Groups pane to the left of the path diagram, ensure that Control is selected.
This indicates that the path diagram for the control group is displayed in the drawing
area.
pre_verbal
pre_syn
0,
eps1
1
1
pre_opp
0,
eps2
1
post_verbal
post_syn
0,
eps3
post_opp
0,
eps4
1
1 1
0,
zeta
1