From: Douglas Bates <dmbates_at_gmail.com>

Date: Tue 21 Jun 2005 - 01:10:48 EST

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Jun 21 01:20:10 2005

Date: Tue 21 Jun 2005 - 01:10:48 EST

On 6/20/05, Spencer Graves <spencer.graves@pdf.com> wrote:

> (comments in line)

*>
**> Stephen wrote:
**> > Dear Fellow R users,
**> >
**> >
**> >
**> > I am fairly new to R and am currently conducting a mixed model.
**> >
**> >
**> >
**> > I have 7 repeated measures on a simulated clinical trial
**> >
**> >
**> >
**> > If I understand the model correctly, the outcome is the measure (as a
**> > factor) the predictors are clinical group and trial (1-7). The fixed
**> > factors are the measure and group. The random factors are the intercept
**> > and id and group.
**> >
**> >
**> >
**> > Based on this
**> >
**> > Dataset <- read.table("C:/Program Files/R/rw2010/data/miss/model1.dat",
**> > header=TRUE, sep="\t", na.strings="NA", dec=".", strip.white=TRUE)
**> >
**> > require (nlme)
**> >
**> > model.mix <- lme (trans1 ~ Index1 + grp,
**> > random = ~ constant | id / grp ,
**> > data = Dataset,
**> > na.action = "na.exclude")
**>
**> I'm not familiar with this syntax. I would replace your "random"
**> formula with "~1|id/grp". Did you get sensible results from your
**> attempt to compute "model.mix"? How do the results compare with the
**> results from replacing your "random" with "~1|id/grp"? Also, I'd try
**> the same thing with lmer; please see "Fitting Linear Mixed Models in R"
**> by Doug Bates in the latest R News, downloadable from
**> "www.r-project.org" -> Newsletter.
*

The syntax in lmer would be

model.mix <- lmer(trans1 ~ Index1 + grp + (1|id:grp) + (1|id), Dataset, na.action = na.exclude)

*> >
*

> > # where trans1 is the factor of the repeated measures of the scale.

*> >
**> > # Index is the trial number, grp the group, and id the subject number.
**> >
**> >
**> >
**> > I would like to split the results, just like SPSS splitfile by a
**> > variable in the Dataset called runnb
**> >
**> > I have tried using:
**> >
**> >
**> >
**> > by (Dataset, runnb,
**> >
**> > function (x) (lme (trans1 ~ Index1 + grp,
**> >
**> > random = ~ constant | id / grp ,
**> >
**> > data = Dataset,
**> >
**> > na.action = "na.exclude") )
**> >
**> > )
**> >
**> I haven't used "by" enough to comment on this. If I had problems
**> with something like this, I might do something like the following:
**>
**> with(Dataset, table(runnb, id, grp))
**>
**> Do you have enough observations in all cells to be able to estimate
**> all these individual models? If yes, I might proceed as follows:
**>
**> b.lvls <- table(Dataset$runnb)
**> nb <- length(b.lvls)
**> fit <- vector(mode="list", nb)
**> for(i in 1:nb)
**> fit[[i]] <- lme(...)
**>
**> If I still had problems with this, I might manually step through this
**> until I found the "i" that created the problem, etc.
**> >
**> >
**> > but to no avail . as my computer hangs and I set my GUI to --mdi
**> > --max-mem-size=1200M.
**> >
**> >
**> >
**> > Any ideas as to how to splitfile the results SPSS style would be most
**> > appreciated?
**> >
**> >
**> >
**> > Also, does lme do pairwise deletion?
**> >
**> >
**> >
**> > By the way
**> >
**> >
**> >>version
**> >
**> >
**> > platform i386-pc-mingw32
**> >
**> > arch i386
**> >
**> > os mingw32
**> >
**> > system i386, mingw32
**> >
**> > status
**> >
**> > major 2
**> >
**> > minor 1.0
**> >
**> > year 2005
**> >
**> > month 04
**> >
**> > day 18
**> >
**> > language R
**> >
**> > Windows XP Pro.
**> >
**> >
**> >
**> > Many thanks
**> >
**> > Stephen
**> >
**> > Ps as its my first time on this group - neat program!
**> >
**> >
**> > ???? ?"? ???? ????
**> > **http://mail.nana.co.il
**> >
**> > [[alternative HTML version deleted]]
**> >
**> > ______________________________________________
**> > R-help@stat.math.ethz.ch mailing list
**> > https://stat.ethz.ch/mailman/listinfo/r-help
**> > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
**>
**> ______________________________________________
**> R-help@stat.math.ethz.ch mailing list
**> https://stat.ethz.ch/mailman/listinfo/r-help
**> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
*

>

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Jun 21 01:20:10 2005

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