Dear Emla,
It seems to me that you may have hit in the problem. Try removing
one of the duplicated covariates and see if the problem goes away.
Ray
Ray C Boston, PhD
Professor of Biomathematics and Biostatistics
Dept. of Clinical Studies, NBC
School of Veterinary Medicine
382 West Street Road Kennett Square, PA 19348
Phone 610 444 5800 (X 2557)
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