Inter occasion variability

From: Sriram Krishnaswami <ksriram@ufl.edu> Subject: Inter occasion variability Date: Sat, 26 Feb 2000 13:18:17 -0500 Dear NMusers I am trying to PK/PD model a rich data set comprising 14 subjects. I basically have the PK profile, the baseline PD profile (endogenous cortisol) over 24 hours (because cortisol exhibits circadian rhythm) and the drug induced PD (Suppressed cortisol levels) profile over 24 hours. I am currently doing the two-stage procedure of fitting each individual using a well established PK/PD model and finally hope to use means and SDs to make some sense out of them. But, I find that in some cases (actually half of the patients), the drug induced levels of cortisol are higher than the baseline levels. The study was part of a lenghty crossover design with patients taking placebo over 5 days followed by 3 weeks washout and then followed by the drug treatment over 5 days. We are wondering if this is due to inter occasion variability. Would this be a candidate to evaluate inter-occasion variability? If so , please suggest a way to do this. If my understanding is right, one usually does inter-occasion variability if the same conditions are repeated on a different occasion. In our case, in one occasion we have the placebo effect and in the other occasion we have the drug effect. Thanks in advance Sriram