Nurse-practitioners are nurses with advanced qualifications who often act much like primary-care physicians. Are they as effective as doctors at treating patients with chronic conditions? An experiment was conducted with 1316 patients who had been diagnosed with asthma, diabetes, or high blood pressure.

Within each condition, patients were randomly assigned to either a doctor or a nurse-practitioner. The response variables included measures of the patients’ health and of their satisfaction with their medical care after 6 months.

a. Which are the blocks in this experiment: the different diagnoses (asthma, diabetes, or high blood pressure) or the type of care (nurse or doctor)? Why?

b. Explain why a randomized block design is preferable to a completely randomized design in this context.

c. Suppose the experiment used only diabetes patients, but there were still 1316 subjects willing to participate. What advantage would this offer? What disadvantage?