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

[Farrar, David]

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

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