[R] effects packages for mixed model?

John Fox jfox at mcmaster.ca
Mon Jan 17 15:39:13 CET 2011

Dear John,

I've wanted to extend the effects package to mixed-effects models for some
time now. The basics are quite simple and you should be able to do the
computations yourself using the estimated fixed effects and their covariance

The tricky computations are for models that have data-dependent bases, such
as those including regression spline or orthogonal polynomial terms. In the
limited time I've had to look at the problem, I haven't figured out how to
get so-called safe predictions for mixed models. Simply using predict()
isn't sufficient, since the effect() function has to manipulate the model
matrix directly.


John Fox
Senator William McMaster
  Professor of Social Statistics
Department of Sociology
McMaster University
Hamilton, Ontario, Canada

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
> On Behalf Of array chip
> Sent: January-17-11 1:08 AM
> To: r-help at r-project.org
> Subject: [R] effects packages for mixed model?
> Hi, I am wondering if there is a similar effects package for mixed
> models, just like what effects package does for linear, generalized
> linear models?
> Specifically I am looking for a way to calculate the SAS-co-called least
> squared means (LS means) in mixed models (I understand there is a
> substantial debate on whether such adjusted means should be computed in
> the first place).
> Thank you,
> John
> 	[[alternative HTML version deleted]]
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