st: xtmixed syntax

[David Airey <david.airey@vanderbilt.edu>]

.

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?

-Dave

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