Question

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 intervention.

Participant ID	Before Intervention	After Intervention
1	75%	80%
2	82%	84%
3	66%	70%
4	74%	70%
5	88%	90%
6	66%	75%
7	51%	60%
8	93%	90%
9	88%	90%
10	91%	95%

Answer 1

Participant ID	Before Intervention (B)	After Intervention (A)	D = A - B	(D - M) ^2
1	75%	80%	5%	0.0004
2	82%	84%	2%	1E-04
3	66%	70%	4%	1E-04
4	74%	70%	-4%	0.0049
5	88%	90%	2%	1E-04
6	66%	75%	9%	0.0036
7	51%	60%	9%	0.0036
8	93%	90%	-3%	0.0036
9	88%	90%	2%	1E-04
10	91%	95%	4%	1E-04
Total			30%	0.0166

1. The mean difference score is M = = = 3%

2. Estimated standard deviation of difference mean score is

                                     S= =    = 0.043

The standard deviation of the difference in adherence before versus after intervention is 0.043