Conditioning on certain random events associated with statistical variability in PK/PD

In PK/PD data analysis, statistical models involving random variables are developed. At times an analysis can be carried out by conditioning on certain random events involving these variables. This paper attempts to clarify issues regarding conditioning. In particular, conditioning is examined as it relates to a number of disparate practical matters: missing covariate values, dose titration, BQL data, "no change from baseline" data, and the use of a truncated intraindividual probability distribution for PK observations.