[R] linear mixed model?

Dave Sun
2007-03-27T16:40:37Z

Hi,
I got the following example from MASS (10.2 Classic Nested Designs)

"A cooperative trial in analytical chemistry taken from Analytical Methods
Committe (1987). Seven specimens were sent to six laboratories, each three
times a month apart for duplicate analysis. The response is the
concentration of (unspecified) analyte in g/kg".

I understand what is written in the book about the linear mixed model
(nested). Laboratories and batches are treated as random and to assess
components of variation. However, I have an extral question about it. From
the analysis, we can evaluate the variance from different labs. Let's say a
training program was done to the labs, I want to see whether after the
trainning program, the variance from the lab (sigma_L in the book) becomes
smaller or not. Basically I need to compare \sigma_L before and after the
training program. How can I do that? I think there should already be some
model for this type of analysis.

Thank you in advance.
Dave

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