RE: sample size

From: "Mats Karlsson" mats.karlsson@farmbio.uu.se Subject: RE: [NMusers] sample size Date: Mon, November 15, 2004 5:15 am Hi Steve and Pascal, Steve, Even in the case you have some information about your system, I don't see how the performing an assessment on the design before analyzing the data is more informative than analyzing the data and then assess the appropriateness of the design. Your guess at what the true model is must be better after looking at the data. I can't imagine the situation where you would 1) guess at the appropriate model, 2) assess the design and find that it is not sufficient to characterize it, and therefore 3) throw away your data. You are always going to analyse your data so why not take advantage of the information you gain. Pascal, I just reacted to your statement "I would certainly not use populaton analysis with 4 individuals even if NONMEM or any other algorithm gives you estimates." As it seems, we all agree that population, or non-linear mixed effects, modeling actually may be the way to go here even if the amount of information is limited with only 4 subjects.* Also, I do believe we are interested in information about population parameters, not individual parameters (unless we want to treat these specific 4 large mammals). These individuals are of interest only because they can tell us something about the population. The information will be very scarce, but it will be information about the population. *My guess is that nonlinear mixed effects modeling may be best, but wouldn't be surprised is in some situations (balanced design, not very nonlinear systems, ...) nave pooling could give more precise and less biased estimates for some population parameters. Best regards, Mats -- Mats Karlsson, PhD Professor of Pharmacometrics Div. of Pharmacokinetics and Drug Therapy Dept. of Pharmaceutical Biosciences Faculty of Pharmacy Uppsala University Box 591 SE-751 24 Uppsala Sweden phone +46 18 471 4105 fax +46 18 471 4003 mats.karlsson@farmbio.uu.se