Question 1: The following data were presented summarizing the background characteristics of 50 participants in a research study evaluating HIV medications.
|
Patient Characteristics
|
Mean (SD)/%
|
|
Age, years
|
37.6 (6.8)
|
|
% Male
|
75.1%
|
|
Education, years
|
13.6 (2.4)
|
|
Annual Income, $000s
|
31.4 (5.2)
|
|
CD4 Cell Count, cells/μ1
|
376 (94)
|
a) Construct a 95% confidence interval estimate of the mean CD4 cell count.
b) How many subjects would be required to estimate the mean CD4 cell count within 15 cells of the true value with 95% confidence?
Question 2: We wish to design a study to estimate the mean weight loss (in pounds) among participants in a study of a newly developed weight loss drug. How many subjects would be required to ensure that the estimate is within 2 pounds of the true mean with 95% confidence ?
A published study of a similar drug reported the following:
|
Number of subjects |
Mean |
Variance |
Median |
Range |
| Weight Loss(pounds) |
125 |
53 |
14.4 |
6.1 |
0-15 |
Question 3:
A recent article appeared in Medical Care describing the health status of HIV-infected patients. Based on the Centers for Disease Control classification algorithm, patients were classified into one of three HIV disease stages: Asymptomatic, Symptomatic or AIDS. Demographic characteristics of the study sample were provided in the article and are summarized below:
| Demographic Charaterstics by HIV Disease Stage |
|
Asymptomatic |
Symptomatic |
AIDS |
| n |
40 |
49 |
71 |
| Mean age (± SE) |
37.7 ± 1.3 |
36.1 ± 1.2 |
36.6 ± 1.0 |
| Male (%) |
70 |
61 |
68 |
a. Is there a relationship between disease stage and age ? If yes, what is the nature of the relationship ? Explain (briefly).
b. Compute a 90% confidence interval for the mean age of Asymptomatic patients.