[R] lsmeans

John Fox jfox at mcmaster.ca
Sat Jun 7 22:02:31 CEST 2008

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.


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]
> Behalf Of Dieter Menne
> Sent: June-07-08 4:36 AM
> To: r-help at 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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