TO THE EDITOR: We read the recent article on olanzapine by Gary D. Tollefson, M.D., Ph.D., and colleagues (1) and wish to comment on several issues. The authors' methodological choices were interesting. Combining patients from distinct diagnostic groups and of different severity levels can lead to analytic difficulties. Also, patient exclusion criteria were not listed. Were patients with comorbid substance abuse or who were taking depot antipsychotic medications excluded from the study? While we appreciate the goal of demonstrating efficacy in a diverse group of patients, pooling data from several distinct groups opens the possibility that important findings will be overlooked.