[R] interpreting an LME regression result...
Dieter Menne
dieter.menne at menne-biomed.de
Sat Nov 10 10:22:55 CET 2007
Johan Jackson <johan.h.jackson <at> gmail.com> writes:
>
> In a regression equation not accounting for the fact that people are
> nested in families, the result for Z variable is VERY strong (beta =
> -4511), but this result is much weaker when I use lme and account for
> people nested in families (beta = -2613). I'm struggling with a verbal
> interpretation of this result. Is it because the effect of Z within
> families is not very strong, but between family variation is high?
>
> -----------------------------------------------------------------
>
> If my R syntax would be helpful, it's below:
>
> BIG EFFECT OF Z (using lm)
> summary(lm(Y ~ X + Z + age ,data=pharma.data ,na.action='na.omit'))
... omitted (gmane complains when you quote too much)
Try to check the results for both cases with an XZ interaction. Possibly lme
eats part of the effect within families that in fact is an interaction.
Dieter
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