A medical study is designed to evaluate a new drug, D1, for treating a particular illness. There is a widely used treatment, D2, for this disease to which the new drug will be compared. A placebo will also be included in the study. The researcher has selected 10 hospitals for the study. She does a thorough evaluation of the hospitals and concludes that there may be aspects of the hospitals that may result in the elevation of responses at some of the hospitals. Each hospital has six wards of patients. She will randomly select six patients in each ward to participate in the study. Within each hospital, two wards are randomly assigned to administer D1, two wards to administer D2, and two wards administer the placebo. All six patients in each of the wards will be given the same treatment. Age, BMI, blood pressure, and a measure of degree of illness are recorded for each patient upon entry into the hospital. The response is an assessment of the degree of illness after 6 days of treatment.