Hi Rob
A couple of suggestions
1. You can use the glht command in the multcomp to get predictions for
different factor levels with simultaneous se's / ci's, you just need to
formulate the correct contrast(s)
2. You can make ad-hoc predictions by matrix-multiplying the parameter
estimates (from fixef()) from the model with the model.matrix() of explanatory
variables, and get the se's by additionally including the variance-covariance
matrix of the fixed effects. Please contact me off-list if you'd like some
example code - I have some but it was provided to me by a colleague and I'd
prefer not to broadcast it indiscriminately as it isn't my invention
3. I haven't looked at them, but the packages zelig and ez may also help
4. It isn't a dumb question, it's taken me ages to get even this far (not very
far)!
Cheers
Mike
-Original Message-
From: r-sig-ecology-boun...@r-project.org
[mailto:r-sig-ecology-boun...@r-project.org] On Behalf Of Rob Knell
Sent: 06 September 2011 14:22
To: r-sig-ecology@r-project.org
Subject: [R-sig-eco] plot confidence intervals of a line from a mixed model
Hello everyone
I'm afraid this is probably a very dumb question, but I have ended up totally
stumped in trying to do this. I have a mixed model fitted to some data using
lme, including a fixed effect that is an interaction term between a factor
(maternal treatment) with two levels and a continuous variable (weight). I'd
like to plot a graph showing the two fitted lines plus their confidence
intervals. How do I get the confidence intervals? I can get the standard error
of the difference between the two slopes from summary(model), but that's not
what I want. I can get the confidence intervals for the difference between the
slopes with intervals(model) but again that is for the difference between the
slopes. I tried using predict(model,...,int=c) but the int=c call doesn't
seem to work with an lme object. Any suggestions gratefully received.
Rob K
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