[R] Variance explained in mixed models

[Doran, Harold]

Ahh, the key to getting what you want is to ask the same question over
and over again. This question is not about R and an answer can be found
in all basic books on hierarchical linear models. 

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Simon Pickett
> Sent: Friday, August 31, 2007 9:43 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Variance explained in mixed models
> 
> Hi,
> 
> I realise this has come up before in various reincarnations 
> but I couldnt find the answer...
> 
> I wish to quote the "percentage variance explained" by each 
> of three components in my mixed model, one random effect and 
> two fixed effects.
> 
> lmer(response~x1+x2+(1|random), data=data)
> 
> Using lmer I can get the variance explained by the random 
> effect but not the fixed effects obviously.
> 
> I was using a suggestion by someone that you can compare the 
> variance components of the model with with both fixed terms 
> included, with another model that has one of the fixed terms 
> removed. When I did this the Variance + residual variance did 
> not add up to the same figure each time.
> 
> #first model with both fixed terms
>           Variance StdDev
> (Intercept) 1.074666 1.036661
> Residual    1.136264 1.065957
> 
> #second model with one term ommitted
>             Variance StdDev
> (Intercept) 1.113713 1.055326
> Residual    1.154527 1.074489
> 
> #third model with the other term ommitted Variance StdDev
> (Intercept) 1.069478 1.034156
> Residual    1.145590 1.070322
> 
> Actually the second model with only one fixed effect is 
> saying that the percentage variance explained is higher than 
> the one with both fixed effects which is impossible right?
> 
> Any better ideas?
> 
> Thanks in advance, Simon.
> 
> 
> Simon Pickett
> PhD student
> Centre For Ecology and Conservation
> Tremough Campus
> University of Exeter in Cornwall
> TR109EZ
> Tel 01326371852
> 
> http://www.uec.ac.uk/biology/research/phd-students/simon_pickett.shtml
> 
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