[R] repeated measures nonlinear regression

Wayne Hallstrom wayne.hallstrom at ualberta.ca
Mon Feb 16 11:25:25 CET 2004

I found this email on the R website.  I am trying to figure out how to
analyse a data set that I believe will need to be run through a procedure
involving repeated measures, regression and mixed models.

The data is of insect populations (dependent variable - either 0/1=binomial,
or as counts=poisson) in sites with different characteristics (multiple
independent variables which are both categorical and continuous).  These
populations were repeatedly sampled (an unequal number of times) at different
times during the year.

The standard stats packages are not able to do what I would like to do.  Any 
suggestions for some alternative methods such as those which are specially 
programmed for R and are suited to the type of data which I am analysing?  I 
understand I will need a flexible repeated measures application to be able to 
accept the unequal sampling.  I also will need a gnlm regression to fit the 
general data structure.  And also, I think, the mixed models capability in 
order to fit in the true nature of the data (see next paragraph).

Lastly, I have a question about independent variables.  For example, I have a
measure for host plant density at a site, which I am using as a
predictive/independent variable to compare with the insect population/response
variable.  However, the values for the host plant data at each site are 
produced by many samples taken in the site to derive a mean. The normal method 
in ecology is to then use this mean as 'the' host plant value for that site in 
your analysis.  I don't think this represents the full qualities of the data, 
and would like to be able to include the fact that this is really a mean +/- 
SD into the final statistical model, since this is what it really is, not just 
a single perfect value.  Any suggestions on how to do this?  I thought maybe a 
generalized linear mixed model (glmm) might allow this type of analysis to be 
done.  Perhaps it could be accomplished with some restructuring of the data?  
>From my reading about statistics I gather it is a general problem in 

Thank you for your time,
Wayne Hallstrom

Wayne Hallstrom
Department of Biological Sciences
CW 405, Biological Sciences Centre
University of Alberta
Edmonton, Alberta
Canada, T6G 2E9 
Telephone: (780) 492-1180
Fax: (780) 492-9234

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