Message-ID: <479F3792.7060905@bio.ntnu.no>
Date: 2008-01-29T14:26:26Z
From: Henrik Pärn
Subject: random factor of type integer
Dear all,
I have a dataset where the variables that I later will use as random
grouping factors in a lmer-model are integers. Do I first need to
convert them to factors?
I just tried if the example on the help page for lmer (where the
grouping factor 'Subject' actually is a factor)...
str(sleepstudy$Subject)
fm1 <- lmer(Reaction ~ Days + (Days|Subject), sleepstudy)
summary(fm1)
...differed from:
Subject2 <- as.integer(as.character(sleepstudy$Subject))
fm2 <- lmer(Reaction ~ Days + (Days|Subject2), sleepstudy)
summary(fm2)
...but it did not.
Is this a general case or could the use of a random factor of integer
type may cause problems in lmer?
Thanks in advance!
Henrik