A long--standing problem in clinical research is distinguishing drug treated subjects that respond due to specific effects of the drug from those that respond to non-specific (or placebo) effects of the treatment. Linear mixed effect models are commonly used to model longitudinal clinical trial data. A solution to this problem is presented using an optimal partitioning methodology for linear mixed effects models. The approach is compared and contrasted with a growth mixture model approach. The methodology is applied to a twophase depression clinical trial where subjects in a first phase were treated openly for 12 weeks with fluoxetine followed by a double blind discontinuation phase where responders to treatment in the first phase were randomized to either stay on fluoxetine or switched to a placebo.
Available at: http://works.bepress.com/thaddeus_tarpey/52/