[R] SEM interaction

Anthony Dick
Tue, 25 May 2010 15:38:24 -0000

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

--
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/