Re: [R] lsmeans

From: John Fox <jfox_at_mcmaster.ca>
Date: Sat, 07 Jun 2008 16:02:31 -0400

Dear Dieter,

I don't know whether I qualify as a "master," but here's my brief take on the subject: First, I dislike the term "least-squares means," which seems to me like nonsense. Second, what I prefer to call "effect displays" are just judiciously chosen regions of the response surface of a model, meant to clarify effects in complex models. For example, a two-way interaction is displayed by absorbing the constant and main-effect terms in the interaction (more generally, absorbing terms marginal to a particular term) and setting other terms to typical values. A table or graph of the resulting fitted values is, I would argue, easier to grasp than the coefficients, the interpretation of which can entail complicated mental arithmetic.

Regards,
 John



John Fox, Professor
Department of Sociology
McMaster University
Hamilton, Ontario, Canada
web: socserv.mcmaster.ca/jfox

> -----Original Message-----
> From: r-help-bounces_at_r-project.org [mailto:r-help-bounces_at_r-project.org]
On
> Behalf Of Dieter Menne
> Sent: June-07-08 4:36 AM
> To: r-help@stat.math.ethz.ch
> Subject: Re: [R] lsmeans
>
> John Fox <jfox <at> mcmaster.ca> writes:
>
> > I intend at some point to extend the effects package to linear and
> > generalized linear mixed-effects models, probably using lmer() rather
> > than lme(), but as you discovered, it doesn't handle these models now.
> >
> > It wouldn't be hard, however, to do the computations yourself, using
> > the coefficient vector for the fixed effects and a suitably constructed
> > model-matrix to compute the effects; you could also get standard errors
> > by using the covariance matrix for the fixed effects.
> >
>
> >> Douglas Bates:
> https://stat.ethz.ch/pipermail/r-sig-mixed-models/2007q2/000222.html
> >>
> My big problem with lsmeans is
> that I have never been able to understand how they should be
> calculated and, more importantly, why one should want to calculate
> them. In other words, what do lsmeans represent and why should I be
> interested in these particular values?
> >>
>
> Truly Confused, torn apart by the Masters
>
> Dieter
>
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