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st: xt?

From   David Airey <david.airey@Vanderbilt.Edu>
Subject   st: xt?
Date   Wed, 12 Jun 2002 13:13:19 -0500

Dear Listmembers,

I have a set of 10 inbred mouse strains, 20 per strain, 200 mice total. Because each strain is inbred, they have the same genes (like twins or clones). Thus variation within strain is environmental, between strain is genetic. I want to remove environmental and genetic variation from one measure that is associated with another. In this case I have a size measure of a brain part that correlates, not surprisingly, with total brain size. I want to remove variation associated with brain size from the brain part measure.

I was wondering if this is a situation for xt models? With regression the problem is that the animals within strain are cannot be considered independent. With ANCOVA I cannot assume parallel lines among strains for the relation between brain part and brain.

brain part = constant + brain + strain + (mouse nested in strain) + error

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