[R] SEM interaction

Anthony Dick adick at uchicago.edu
Tue May 25 17:38:24 CEST 2010

Hello all,

This is a general stats question--I realize it is an R help list, so 
tell me to go away if it is inappropriate.

I have a 2 X 2 design, and I have specified four identical path models 
(one for each level of each factor). I want to test for an interaction 
at each path--essentially (A1 - A2) - (B1 - B2) != 0. I was thinking of 
computing a contrast for each path of interest, such that I compute the 
difference of the difference in the (non-standardized) path weights (as 
above), and then divide this by the pooled standard errors of the 
estimates (average of the standard errors).

Does this seem statistically sound, or am I way off base? I typically 
compare path weights across two levels (e.g., age differences in a path 
weight for the same theoretical model) using the stacked model approach, 
but am not sure how to apply this to the interaction.


Anthony Steven Dick, Ph.D.
Post-Doctoral Fellow
Human Neuroscience Laboratory
Department of Neurology
The University of Chicago
5841 S. Maryland Ave. MC-2030
Chicago, IL 60637
Phone: (773)-834-7770
Email: adick at uchicago.edu
Web: http://home.uchicago.edu/~adick/

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