# PharmPK Discussion - Sample design

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• On 11 Dec 2009 at 15:43:47, Qi Feng (luckystar204.aaa.gmail.com) sent the message
`Hello, everybody.I want to optimize my sample designs badly, However the software AdaptII  needs the users to offer the parameters sigma inter(SDinter) and sigma  slope(SDslope) themselves. Unfortunately, the authors only afforded the  variance model description : var{v(t)} =(sigma inter + sigma  slopey(t))2. As an example assume sigma inter =0.0and sigma slope =0.1  in Eq. (2.9). Then the variance model represents an error process with  a standard deviation of 10% of the measured quantity (i.e.,10%  coe\0xFB03cient of variation). While there is another different  explanations for the two parameters of the same model: where sigma inter   is closely related to the sensitivity of the analytical method and  sigma slope is closely related to the coefficient of  variation(abbreviated from Thesis of Pakawadee Sermsappasuk). Especially  for the meaning of sigma slope, there exist contradictions. So my  questions are listed as follows: firstly, which is the purpose of sample  design, optimizing subsequent formal large sample size exp`
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• On 11 Dec 2009 at 13:46:18, "Lavigne, Jean" (Jean.Lavigne.-at-.mdsinc.com) sent the message
`The following message was posted to: PharmPKDear Dr. Qi Feng,From what I understand from ADAPT II, you do not necessary need to  have a variance model equal to (SDslope*Y + SDinter)^2; it is an error  model suggested in the documentation of ADAPT II.  Other type of error  model could be used.  The purpose of optimal sampling design is to get  the most information from you data with the minimum of samples based on  the a priori the model and variance, at least this how I interpret it.If you already have data, fit them (with ADAPT or your favorite  software) and then you can use these parameters in the optimal sampling  of ADAPT.  Perhaps it would be of interest to you to know that ADAPT 5  is now available athttp://bmsr.usc.edu/Software/ADAPT/ADAPT.htmlI would use either ITS or MLEM module of ADAPT 5 to get population  estimates.I hope this help!Jean--Jean R. Lavigne M.Sc.Associate Director, Clinical PharmacologyMDS Pharma Services4705 DobrinSt-Laurent, Quebec, CanadaH4R 2P7`
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