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Running repeated measures in lme4

5 messages · Emma Stone, Ben Bolker, Andrew Dolman

Original
Emma Stone
# 
Dear all,

I wander if you can help.

I am running a repeated measures model with lmer.I have 8 sites, at each I 
conducted an experiment with treatments which have 4 levels. Each treatment 
was conducted only once per site, but each site has one of each of the 
treatment levels so it is balanced. Obviously the treatments within sites 
are the repeated measures component, and I want to look at differences 
between treatments within sites, I am not really interested in the site 
group effect but need to incorporate it. So I have set up my model as 
follows:

model1<-lmer~(minutes~treatment+(treatment|site), data = data)


But when I run the model, it gives no variance for the group level effect 
as shown below.

Random effects:
 Groups   Name        Variance Std.Dev. Corr
 site     (Intercept) 0.00000  0.00000
          treatment   0.00000  0.00000    NaN
 Residual             0.07707  0.27762
Number of obs: 32, groups: site, 8

Is this because I only have one replicate of each treatment level at each 
site? Can anyone help?

Thanks

Emma
University of Bristol
Ben Bolker
#
Emma Stone wrote:
This model fits a site by treatment interaction, which you don't
have enough information for since you don't have replication.  I believe
you want

model1<-lmer~(minutes~treatment+(1|site), data = data)
Emma Stone
# 
Hi Ben,

Thanks for your reply, however I have re ran this and I still get zero 
group variance. Also, forgive my ignorance but doesn't this code remove the 
repeated measures element of the design? Also for note, I ran my code with 
a poisson distribution and I did get variance outputs for the Random Group 
level.

Emma
--On 03 March 2010 07:28 -0500 Ben Bolker <bolker at ufl.edu> wrote:

            

      
      
      
    

        
----------------------
Emma Stone
Postgraduate Researcher
Bat Ecology and Bioacoustics Lab
& Mammal Research Unit
School of Biological Sciences,
University of Bristol, Woodland Road,
Bristol, BS8 1UG
Email: emma.stone at bristol.ac.uk