[R-sig-ME] lmer random and fixed effect?

[Ben Bolker]

  In this example:

lmer(formula = extro~open+agree+social+class+(1|school/class),
     data = lmm.data)

  'class' is included as a fixed effect, and the random effects grouping
variable is specified as school/class, which means "class nested within
school", i.e. the same as school+school:class (where : denotes
interaction).  Note that class itself is *not* included as a
random-effects grouping variable.   This model specification would make
sense if (1) levels of the class variable are defined across schools
(i.e. class #1 in school #1 has something in common with class #1 in
school #2); (2) it makes sense to treat class as a fixed effect, i.e. we
have a fairly small number of classes and/or we want to make inferences
about the values of particular classes contrasts among specific classes
(and not just the variation among classes)


On 14-08-14 02:25 PM, Farrar, David wrote:
> 
> 
> A split-plot design is an example where both are used.  You may find
> helpful the discussion of that design "the R book."
> 
> -----Original Message----- From:
> r-sig-mixed-models-bounces at r-project.org
> [mailto:r-sig-mixed-models-bounces at r-project.org] On Behalf Of
> Charles Determan Jr Sent: Thursday, August 14, 2014 2:09 PM To:
> r-sig-mixed-models at r-project.org Subject: [R-sig-ME] lmer random and
> fixed effect?
> 
> Greetings,
> 
> I have been looking more into mixed models recently and have run into
> a situation that confuses me.  I was initially under the impression
> that fixed and random effect variables are separate, however can they
> be both in an lmer model and if so why would you do so?
> 
> Such as example is with the following dataset: lmm.data <-
> read.table(" 
> http://www.unt.edu/rss/class/Jon/R_SC/Module9/lmm.data.txt", 
> header=TRUE, sep=",", na.strings="NA", dec=".", strip.white=TRUE)
> 
> Reading online, I have found the following model: require(lme4) fit
> <- lmer(formula = extro~open+agree+social+class+(1|school/class),
> data = lmm.data)
> 
> Everything runs fine but I am confused as to what this actually means
> or if it is even appropriate.
> 
> Thank you for any insight, Regards,
> 
> -- Dr. Charles Determan, PhD Integrated Biosciences
> 
> [[alternative HTML version deleted]]
> 
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