<qa>  What is the purpose of using placebo?This is a 12-week study which investigates the use of olanzapine to decrease disruptive behaviors sometimes associated with Autism in children, aged 3 to 12 years old. The first six weeks of the study are double-blind and placebo controlled, meaning that patients receive either placebo or olanzapine, and that neither the researchers nor the patients know whether or not they are receiving placebo or olanzapine. In the second six weeks all of the patients receive olanzapine. The purpose in using placebo is that it is otherwise impossible to know how effective the drug is or whether or not the drug causes side effects. Patients treated with placebo can have improvement and can have side effects. In the study patients receive a psychiatric evaluation, physical examination, laboratory tests, and study medication olanzapine or placebo, free of charge. 