You conduct a study in which you compare the blood pressure of three groups of people diagnosed with hypertension, one group taking a standard blood pressure medication, one group taking a new treatment, and a third group assigned to a strict diet and exercise protocol. The patients were allowed to choose which treatment they wanted to try. You measure the patients' blood pressure 6 months after the patients began their treatment. Which would be the best null hypothesis to test using ANCOVA in this study?

Select one:

a.

There is no difference in the probability of having hypertension 6 months after treatment in the three groups.

b.

There is a small difference in the mean blood pressure 6 months posttreatment in the three groups after adjusting for pretreatment blood pressure and other potential confounders.

c.

There is no difference in the mean blood pressure 6 months posttreatment in the three groups after adjusting for pretreatment blood pressure and other potential confounders.

d.

There is no difference in the mean blood pressure at 6 months posttreatment in the three groups.