Dear list
I need confirmation or correction on this: how can the structure of  
the R vcv matrix of a LMM have non negative covariances if the  
residuals are independent given the random effects (and the co- 
variates)?  Covariance structures such as compound symmetry, AR 1,  
Toeplitz are specified by the user or are the marginal type of vcv  
implied/induced by the random effects?
Thank you
Pietro

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Dr. Pietro Ravani, MSc (Biostatistics), MD, FNCPI
Associate Professor - Division of Nephrology
Departments of Medicine & Community Health Sciences
Faculty of Medicine - University of Calgary
Foothills Medical Centre - AB Health Services - CHR
1403 - 29th Street N.W. (room C210N)
Calgary, AB, Canada, T2N 2T9
T 403-944-8168; F 403-944-2876; E pravani@ucalgary.ca
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