[R] Basic LME
Martin Hoyle
plxmh at nottingham.ac.uk
Tue Apr 8 16:08:32 CEST 2003
Hello R Users,
I am investigating the basic use of the LME function, using the following example;
Response is Weight, covariate is Age, random factor is Genotype
model.lme <- lme (Weight~Age, random=~ 1|Genotype)
After summary(model.lme), I find that the estimate of Age is 0.098 with p=0.758.
I am comparing the above model with the AOV function;
model.aov <- aov (Weight~Age + Genotype)
I find that the estimate of Age is also 0.098, and p=0.758 as in the LME model above.
So, my questions are;
1: I expected that the LME model would be a better way to analyse this data compared to the AOV model, since Genotype is a random factor. However, I obtain the same parameter estimate and p value for Age. Please can someone tell me why?
2: When using LME, when I am after a p value for the covariate Age, is it better to do the following;
Model.lme2 <- lme (Weight~Age, random=~ 1|Genotype, method="ML")
Model.lme3 <- lme (Weight~1, random=~ 1|Genotype, method="ML")
Anova(Model.lme2, Model.lme3)
Giving likelihood ratio=0.102, with p=0.749, which is slightly different to the p values of 0.758 above.
Thanks for your attention,
Martin.
Martin Hoyle,
School of Life and Environmental Sciences,
University of Nottingham,
University Park,
Nottingham,
NG7 2RD,
UK
Webpage: http://myprofile.cos.com/martinhoyle
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