23 Jan MPH501 Quantitative Methods

MPH501 Quantitative Methods for Public Health Application

Module 2 Quiz

Question 1The following are baby height measurements, in cm, for a sample of infants participating in a study of infant health:

28 30 41 48 29 48 62 49 51 39

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 2A pilot study is run to investigate the feasibility of recruiting pregnant women into a study of risk factors for preterm delivery. Women are invited to participate at their first clinical visit for prenatal care. The following represent the gestational ages in weeks of women who consent to participate in the study.

11 14 21 22 9 10 13 18

X X2

11 121

14 196

21 441

22 484

9 81

10 100

13 169

18 324

118 1916

a. Compute the sample mean gestational age.

b. Compute the sample standard deviation of gestational age.

c. Compute the median gestational age

d. What proportion of the sample enroll in first trimester of pregnancy (i.e., between 1-13 weeks, inclusive, of pregnancy)?

Question 3A prospective cohort study is run to estimate the incidence of stroke in persons 55 years of age and older. All participants are free of stroke at study start. Each participant is followed for a maximum of 5 years. The data are summarized below.

Number of Strokes Number of Stroke Free Person-Years

Men (n=125) 9 478

Women (n=200) 21 974

a. What is the annual incidence rate of stroke in men?

b. What is the annual incidence rate of stroke in women?

c. What is the annual incidence rate of stroke (men and women combined)?

Question 4A clinical trial is run to assess the efficacy of a new drug to reduce high blood pressure. Patients with a diagnosis of hypertension (high blood pressure) are recruited to participate in the trial and randomized to receive either the new drug or placebo. Participants take the assigned drug for 12 weeks and their blood pressure status is recorded. At the end of the trial, participants are classified as still having hypertension or not. The data are shown below:

Group Number Randomized Number Free of Hypertension at 12 Weeks

Placebo 50 6

New Drug 50 14

a. What is the prevalence of hypertension at the start of the trial?

b. What is the prevalence of hypertension at the end of the trial?

c. Estimate the relative risk comparing the proportions who are free of hypertension at 12 weeks between groups.