Can anyone tell me the rules/formulae for combining Standard Deviations
or Coefficients of Variation for products and ratios? I haven't been
able to find this covered in statistics texts. I can find a little bit
in Callum Fraser's book, but there's a discrepancy with something I
found in a letter to Clin Chem.
For example, if you know the analytical SD or CV of urea and
creatinine, how would you calculate the SD or CV of the urea/creatinine
ratio? (I can't think of a good practical example of the product of two
analytes. Well, maybe something like the CSF IgG Index = (CSF IgG x
serum Alb)/(CSF Alb x serum IgG), but that can be simplified to all
ratios.)
Thanks. -Jim
James J Miller, Ph.D., DABCC, FACB
Associate Professor, Pathology & Laboratory Medicine
University of Louisville, Louisville, KY 40292
Director of Clinical Chemistry & Toxicology
University of Louisville Hospital Laboratory
[log in to unmask]
Office: 502-852-1179
Pager: 502-478-1219
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