RE: sample size

From:"GIRARD PASCAL" PASCAL.GIRARD@adm.univ-lyon1.fr Subject: RE: [NMusers] sample size Date: Sun, November 14, 2004 3:54 am Hi Vijay, I would certainly not use populaton analysis with 4 individuals even if NONMEM or any other algorithm gives you estimates. Basic idea of parametric population analysis is to estimate parameter statistical distributions, more precisely the first 2 moments mean and variance, of a symetrically distributed random variable . I suggest that, without any fancy population software, you simply try to estimate the mean and variance from 4 simulated normally distributed values, then compute their standard errors of mean and variance. In a second step, try to fit your population model with NONMEM using the data of your 4 mammals and once again have a look at the standard errors of all your parameters (THETA and OMEGA). In both cases, you'll see how bad is the precision of your estimates and realize that they have very little values, except maybe for SIGMA since the estimates will be based on 40 values. The simple laws of statistics still apply in population analysis, which is a powerful tool but certainly not a magic one. Best regards, Pascal ========================================== Dr Pascal Girard EA 3738 Ciblage Thrapeutique en Oncologie Fac Mdecine Lyon-Sud BP12 69921 OULLINS Cedex France Tel 33 4 78 86 31 53 Fax 33 4 78 86 31 49 e-mail : Pascal.Girard@adm.univ-lyon1.fr