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Example 13
exogenous variable has a mean of 0 unless you specify otherwise. You need to use the
Model method once for each exogenous variable whose mean you want to estimate. It
is easy to forget that Amos programs behave this way when you use
ModelMeansAndIntercepts.
Note: If you use the Sem.ModelMeansAndIntercepts method in an Amos program, then
the Mean method must be called once for each exogenous variable whose mean you
want to estimate. Any exogenous variable that is not explicitly estimated through use
of the
Mean method is assumed to have a mean of 0.
This is different from Amos Graphics, where putting a check mark next to
Estimate
means and intercepts
causes the means of all exogenous variables to be treated as free
parameters except for those means that are explicitly constrained.
Model B
The following program (Ex13-b.vb) fits Model B. In addition to requiring
group-invariant variances and covariances, the program also requires the means to be
equal across groups.
Sub Main()
Dim Sem As New AmosEngine
Try
Sem.TextOutput()
Sem.ModelMeansAndIntercepts()
Sem.BeginGroup(Sem.AmosDir & "Examples\UserGuide.xls", "Attg_yng")
Sem.GroupName("young_subjects")
Sem.AStructure("recall1 (var_rec)")
Sem.AStructure("cued1 (var_cue)")
Sem.AStructure("recall1 <> cued1 (cov_rc)")
Sem.Mean("recall1", "mn_rec")
Sem.Mean("cued1", "mn_cue")
Sem.BeginGroup(Sem.AmosDir & "Examples\UserGuide.xls", "Attg_old")
Sem.GroupName("old_subjects")
Sem.AStructure("recall1 (var_rec)")
Sem.AStructure("cued1 (var_cue)")
Sem.AStructure("recall1 <> cued1 (cov_rc)")
Sem.Mean("recall1", "mn_rec")
Sem.Mean("cued1", "mn_cue")
Sem.FitModel()
Finally
Sem.Dispose()
End Try
End Sub