In evaluation research studies, it often occurs that several program participants (experimentals) drop out of the program prior to completion. Since noncompleters generally differ substantially from completers in many respects, a control group which originally was representative of the participant group will most likely not be representative of either the completers or noncompleters considered separately. This paper presents a maximum likelihood procedure for partitioning a control group in such a situation into separate comparison subgroups for assessing program impacts on completers and noncompleters. The approach was used in evaluating the Mountain Plains Career Education Program. (Author)