[R-sig-eco] extracting variance components from lm (Lee, Laura)

[Carl von Ende]

Hi Laura,

To quote the Statsoft Electronic Textbook (Stats), “The basic goal of variance component estimation is to estimate the population covariation between random factors and the dependent variable.”

In using “lm,” you are assuming Station and Year are fixed factors.  Therefore, the only random component is the residual error term. 

To estimate variance components, you must assume either Year or Station is fixed & the other factor random (= mixed model analysis), or that both Year & Station are random.  You will need to use nlme/lmm for the mixed or random analyses. 

Also, re. your R code for the LM, it should be either Year * Station, or Year + Station + Year:Station.

See The R Book, 2nd ed., Michael J. Crawley, Chap. 19 – Mixed-Effect Models, for some examples. 

Hope this helps?

Carl von Ende


On 7/22/17, 5:00 AM, "R-sig-ecology on behalf of r-sig-ecology-request at r-project.org" <r-sig-ecology-bounces at r-project.org on behalf of r-sig-ecology-request at r-project.org> wrote:

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       1. extracting variance components from lm (Lee, Laura)
    
    
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    Date: Fri, 21 Jul 2017 12:19:22 +0000
    From: "Lee, Laura" <laura.lee at ncdenr.gov>
    To: "'r-sig-ecology at r-project.org'" <r-sig-ecology at r-project.org>
    Subject: [R-sig-eco] extracting variance components from lm
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    Hi all-
    
    I have a fairly simple model:
    
    m1 <- lm(Catch ~ Year + Station + Year*Station, data = data)
    
    I would like to extract the among years and year*station variance components and need assistance. I'm aware of the 'varComp' package, but I believe that only applies to nlme and requires a random effect. Any help is greatly appreciated. Thanks!
    
    
    Cheers,
    
    Laura
    
    
    
    Laura M. Lee
    Senior Stock Assessment Scientist
    Division of Marine Fisheries
    Department of Environmental Quality
    
    252 808 8094??? office
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    mailto:Laura.Lee at ncdenr.gov
    
    3441 Arendell Street
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