RE: covariates

From: "Nick Holford" n.holford@auckland.ac.nz Subject: RE: [NMusers] covariates Date: Wed, September 15, 2004 10:22 pm Renee, The first step in covariate analysis is to apply biology not statistics. Your two compartment model has 4 parameters which will vary with weight. So step 1 is to use an allometric model to describe between subject differences in CL, V1, Q, V2. No statistics required. Just do it. Then you might consider other biological covariates e.g. renal function on CL if you think the drug is renally eliminated. Finally you might have to resort to the usual Holy Grail search for effects of age, sex, race, hair colour, etc. IMHO this is mainly a waste of time for any practical application but if you do it then you should read: Ribbing J, Jonsson EN. Power, Selection Bias and Predictive Performance of the Population Pharmacokinetic Covariate Model. Journal of Pharmacokinetics and Pharmacodynamics 2004;31(2):109-134. They caution against Holy Grail searches if you have less than 50-100 subjects in your data base. Nick