[R-sig-ME] Formula Explanation in lme4 Vignette

[Emmanuel Curis]

Hello,

In lme4 formula syntax, random effects factors are on the right side
of the pipe (|). On the left side, you can have only 1 or other fixed
effects factors to include interactions between fixed effects and
random effects factors.

So this example does not violate your lecture, saying that a factor
can be with random or fixed effects, not both : Subject is the random
effect factor, Days the fixed effects, and Days | Subject introduces
an interaction between them --- that is, the Subject random effect is
different for each Days level.

Hope this helps,
Best regards,

On Fri, Nov 14, 2014 at 12:00:17AM +0000, Dario Strbenac wrote:
« Hello,
« 
« In the software article vignette, it says that
« 
« resp ~ FEexpr + (REexpr1|factor1)
« 
« is the general format of mixed models. However, there's a sleep study example which has
« 
« fm1 <- lmer(Reaction ~ Days + (Days | Subject), sleepstudy)
« 
« When I look at those two formulae, I see that Days matches both FEexpr and REexpr1. I thought that a factor could be a fixed effect or random effect, but not both. In lectures, I remember fixed and random effects as being exclusive, depending on if all the levels were measured, or just a subset of them.
« 
« --------------------------------------
« Dario Strbenac
« PhD Student
« University of Sydney
« Camperdown NSW 2050
« Australia
« 
« _______________________________________________
« R-sig-mixed-models at r-project.org mailing list
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-- 
                                Emmanuel CURIS
                                emmanuel.curis at parisdescartes.fr

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