10.49 Does exercise help blood pressure? Several recent studies have suggested that people who suffer from abnormally high blood pressure can benefit from regular exercise. A medical researcher decides to test her belief that walking briskly for at least half an hour a day has the 10.4 Practicing the Basics effect of lowering blood pressure. She conducts a small pilot study. If results from it are supportive, she will apply for funding for a larger study. She randomly samples three of her patients who have high blood pressure. She measures their systolic blood pressure initially and then again a month later after they participate in her exercise program. The table shows the results.

Subject Before After 1 150 130 2 165 140 3 135 120

a. Explain why the three before observations and the three after observations are dependent samples.

b. Find the sample mean of the before scores, the sample mean of the after scores, and the sample mean of the difference scores d = before - after. How are they related?

c. Find a 95% confidence interval for the difference between the population means of subjects before and after going through such a study. Interpret.