23 Jan Question 1 A cohort study

MPH501 Quantitative Methods for Public Health Application

Module 2 Exercise

Question 1 A cohort study is conducted to assess the association between clinical characteristics and the risk of stroke. The study involves n=1,250 participants who are free of stroke at the study start. Each participant is assessed at study start (baseline) and every year thereafter for five years. The following table displays data on hypertension status measured at baseline and hypertension status measured two years later.

2 Years: Not Hypertensive 2 Years: Hypertensive

Baseline: Not Hypertensive 850 148

Baseline: Hypertensive 45 207

a. Compute the prevalence of hypertension at baseline.

b. Compute the prevalence of hypertension at 2 years.

c. Compute the cumulative incidence of hypertension over 2 years.

Question 2A randomized trial is conducted to evaluate the efficacy of a new cholesterol lowering medication. The primary outcome is incident coronary artery disease. Participants are free of coronary artery disease at the start of the study and randomized to receive either the new medication or a placebo. Participants are followed for a maximum of 10 years for the development of coronary artery disease. The following data are observed.

Number of Participants Number with Coronary Artery Disease

Cholesterol Medication 400 28

Placebo 400 42

Some patients were not followed for a total of 10 years. Some suffered events (i.e., developed coronary artery disease during the course of follow-up) while others dropped out of the study. The following table displays the total number of person-years of follow-up in each group.

Number with Coronary Artery Disease

Total Years of Follow-Up

Cholesterol Medication 28 3,451

Placebo 42 2,984

a. Compute the incidence rate of coronary artery disease in patients receiving the new medication.

b. Compute the incidence rate of coronary artery disease in patients receiving placebo.

Question 3A study is run to estimate the mean total cholesterol level in children 2-6 years of age. A sample of 9 participants is selected and their total cholesterol levels are measured as follows.

185 225 240 196 175 180 194 147 223

X X2

147 21,609

175 30,625

180 32,400

185 34,225

194 37,636

196 38,416

223 49,729

225 50.625

240 57,600

1765 352,865

a. Compute the sample mean.

b. Compute the sample standard deviation.

c. Compute the median.

d. Compute the first and third quartiles.

e. Which measure, the mean or median, is a better measure of a typical value? Justify.

f. Which measure, the standard deviation or the interquartile range, is a better measure of dispersion? Justify.

Question 4 The following data were collected as part of a study of coffee consumption among graduate students. The following reflect cups per day consumed:

3 4 6 8 2 1 0 2

X X2

0 0

1 1

2 4

2 4

3 9

4 16

6 36

8 64

26 134

a. Compute the sample mean.

b. Compute the sample standard deviation.

c. Compute the median.

d. Compute the first and third quartiles.

e. Which measure, the mean or median, is a better measure of a typical value? Justify.

f. Which measure, the standard deviation or the interquartile range, is a better measure of dispersion? Justify.

Question 5 In the study of a new anti-hypertensive medication, systolic blood pressures are measured at baseline (or the start of the study before any treatment is administered). The data are as follows:

120 112 138 145 135 150 145 163

148 128 143 156 160 142 150

a. Compute the sample mean.

b. Compute the sample median.

c. Compute the sample standard deviation.

d. Compute the sample range.

e. Are there any outliers? Justify.