R help - Mar 2013 - Extracting coefficients of covariates in a LME-model

Hi all,

I have created a linear mixed-effects model using lmer. My dependent
variable is comp.score and my main independent variable is delay.type, a
repeated-measures within-subject variable (2 levels: Synch and Asynch,
order counter-balanced across participants). I had a series of covariates
that were included in the initial model and used a step-wise process to
produce the most parsimonious model (two covariates age and PLE).

The final model was:

disem<-lmer(comp.score~delay.type+age+PLE+(1|id), data=Disembodiment)



The first 5 rows of the data frame appeared as follows:

head(Disembodiment)

  id          comp comp.score delay.type sex age yrs.edu PLE fds bds

4  C01 Disembodiment  1.3846685      Synch   f  56      14   0   8   6

5  C01 Disembodiment  0.3782303     Asynch   f  56      14   0   8   6

12 C02 Disembodiment  1.4691870     Asynch   f  48      15   0  12  11

16 C02 Disembodiment  1.5863690      Synch   f  48      15   0  12  11

22 C03 Disembodiment -1.3751083     Asynch   m  26      15   0  13  12

23 C03 Disembodiment -0.4114244      Synch   m  26      15   0  13  12



I am at the point where I am creating the plots for the data and I want to
display the effects of each covariate on my dependent variable (a separate
plot for each covariate), which would be achieved by finding the linear
equation for each covariate and plotting it.

e.g.

with(Disembodiment, plot(age, comp.score, ylab="Component Score",
xlab="Age
(years)"))

abline(coef(disem)) ## this doesn’t work but as an example



My question is how do I obtain this information from my model? When I use
summary(disem), I can see the slopes easily enough and I understand that
the intercept is the overall mean for the data, and not the intercept for
the covariates age and PLE. Do I need to alter my model in order to
calculate separate intercepts for each of the covariates and, if so, how?



Thanks for your help!


-- 
Kyran Graham (PhD Candidate)
School of Medicine & Pharmacology, University of Western Australia (M510)
35 Stirling Highway
Crawley, WA 6009
Centre for Clinical Research in Neuropsychiatry, Graylands Hospital
Private Bag No 1
Claremont, WA 6910
Phone: 9347 6430 Email: grahak02@student.uwa.edu.au

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