Re: End of semester MCQ and short answer question

From: "Leonid Gibiansky" leonidg@metrumrg.com Subject: Re: [NMusers] End of semester MCQ and short answer question Date: Sun, July 17, 2005 12:26 pm Nick, Your option d. Using the actual measurement i.e. ask the chemical analyst to tell the truth" should help to limit LLOQ somehow but at the end you will still get some zero values that are measurements below LLOAATDCFZ (lower limit of assay ability to distinguish concentration from zero). Then, you will need to choose among 3 other options: a. Ignoring 0 values b. Using 0 values as 0 c. Imputing 0 values as 0.5*LLOAATDCFZ Remembering the advice of "a prominent user of NONMEM" (I am not sure whether this is the same user as your adviser, but I found on more than one occasion that the advices were good), I usually use (a). Do you have any examples where this would lead to the incorrect model? Also, have you found any examples where option (d) was better (resulted in a more precise or more stable model) than option (a)? Unfortunately, information concerning NONMEM VI is not relevant to the most of mortals except those few who were granted this tool (I guess, as a recognition of the special contribution to the NONMEM development). Thanks Leonid