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st: xtmixed syntax

From   David Airey <>
Subject   st: xtmixed syntax
Date   Thu, 22 May 2008 10:43:44 -0500


I have a variance components mixed model that I am have trouble with syntax using xtmixed. I'm interested in a genetic polymorphism effect (think of this as simple treatment effect) on gene expression, where gene expression is measured on set of genes where genes are actually measured by multiple probes.

two group allelic fixed effect A
random sample effect S, one sample per subject, subjects nested in allelic group, 80 subjects
random gene effect G, measured on all samples, so crossed with group, typically 20-50 genes
random probe effect P, nested in gene, < 5 probes per gene, different probes per gene

So the structure of the data is something like:

(random effect probes nested in random effect genes) crossed with random effect samples

I see examples of two crossed random effects for xtmixed and two-level nested models for xtmixed, but not a combination of these two models. Has anyone modeled a similar variance components model with xtmixed?


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