[R-sig-ME] How does one include a factor in a groupedData object; What is the meaning and use of inner and outer parameters of groupedData object?

Ben Bolker bbolker at gmail.com
Thu Mar 22 19:52:50 CET 2018

  lme4 essentially ignores groupedData information, so I'm not sure
what the goal is here. (Full disclosure:
groupedData was invented for/used in nlme, in principle I think it's a
great idea to incorporate this kind of
metadata system for mixed models, but I've never been able to use it
very effectively myself.)  Are you
trying to run the equivalent model in nlme?  I don't think groupedData
is *necessary* for running an (n)lme model ...

On Thu, Mar 22, 2018 at 11:02 AM, Sorkin, John
<jsorkin at som.umaryland.edu> wrote:
> Several questions relating to groupedData:
> (1) I am trying to create a groupedData object that can be used to run an analysis that I have been able to urn using lmer. When I include the interaction terms in the groupedData opbject I get an error message stating that + is not meaningful for factors. How do I include factors in my model? See code and error below.
> (2) I have read the help file for groupedData multiple times. I am unable to understand the meaning or, or the use for the inner= and outer= parameters in the call to groupedData. Can someone either explain the meaning of these parameters or refer me to a source that give a clear explanation?
>> fit0 <- lmer(THmean~INTRVNTN+factor(TimePtID)+INTRVNTN*factor(TimePtID)+(1|PatientID),data=smalldata)
>> sdgd <- groupedData(THmean~INTRVNTN+TimePtID+INTRVNTN*TimePtID|PatientID,data=smalldata)
> Warning messages:
> 1: In Ops.factor(INTRVNTN, TimePtID) : �+� not meaningful for factors
> 2: In Ops.factor(INTRVNTN, TimePtID) : �*� not meaningful for factors
> Thank you,
> John
> John David Sorkin M.D., Ph.D.
> Professor of Medicine
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology and Geriatric Medicine
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
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