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Adjusted Means

2 messages · Mattune, John Fox

Mattune
# 
I'm running the following ANCOVA model in R: X=a*b*d + d where d is the
covariate.  I want to produce adjusted means for X for all possible
treatment combinations.  a has 6 levels, b has 2 levels, c has 2 levels, so
this is a 6x2x2 = 24 possible treatment combinations.  When I run:
effect("d", Ancova.Model) I am given only 20 adjusted means (also, I'm not
exactly sure of how the adjusted means are reported, that is, which one
represents which treatment combination...what order are they in?)  Any
ideas??

Thanks!
Master's Student in Maine

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John Fox
# 
Dear Mattune,

I guess that you're using the effect() function in the effects package.
You've requested the effect for the covariate fixing the values of the
factors, rather than vice-versa. Try effect("a*b*c", Anocova.Model) or, for
more detail in the output, summary(effect("a*b*c", Anocova.Model)). I
assume, BTW, that you fit the model X ~ a*b*c + d, with d the covariate,
rather than what you said you did.

I hope this helps,
 John

--------------------------------
John Fox
Senator William McMaster
  Professor of Social Statistics
Department of Sociology
McMaster University
Hamilton, Ontario, Canada
http://socserv.mcmaster.ca/jfox
On
treatment
a
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