A pilot study is run to investigate the effect of a lifestyle intervention

designed to increase medication adherence in patients with HIV.

Medication adherence is measured as the percentage of prescribed

pills that are taken over a one-week observation period. Ten patients

with HIV agree to participate and their medication adherence before

and after the intervention are shown below. Compute the standard

deviation of the difference in adherence before versus after the

intervention.

Participant Before After

ID Intervention Intervention

1 75% 79%

2 83% 84%

3 66% 70%

4 79% 68%

5 88% 90%

6 66% 78%

7 55% 60%

8 93% 90%

9 97% 90%

10 91% 95%