Test Bank For Gordis Epidemiology, 7th Edition
Authors: David D. Celentano,Moyses Szklo,Youssef Farag
,Gordis Epidemiology, 7th Edition
Chapter 1 Introduction
Question 1
Measures of disease frequency
A city of 500,000 residents reports 2,500 newly diagnosed cases of tuberculosis during
2026. What is the incidence proportion (cumulative incidence) of tuberculosis for that
year?
A. 0.05%
B. 0.5%
C. 5%
D. 50%
Correct answer
B. 0.5%
Explanation
Incidence proportion = new cases ÷ population at risk = 2,500 ÷ 500,000 = 0.005 = 0.5%.
This measure describes the risk of developing disease during a specified period.
Why the other options are incorrect
• A. 0.05% – Tenfold too low; would correspond to 250 cases.
• C. 5% – Tenfold too high; would correspond to 25,000 cases.
• D. 50% – Grossly overestimates risk; would require 250,000 cases.
Question 2
Prevalence vs incidence
,Researchers observe that the prevalence of a chronic neurologic disease has
increased over the past decade while the incidence has remained stable. Which
explanation is most consistent with these findings?
A. Improved survival among affected patients
B. Reduced duration of disease
C. Decreased case ascertainment
D. Elimination of risk factors
Correct answer
A. Improved survival among affected patients
Explanation
Prevalence depends on both incidence and duration. If incidence remains stable but
patients live longer with the disease, prevalence increases because more people are
living with the condition at any given time.
Why the other options are incorrect
• B. Reduced duration of disease – Would tend to decrease prevalence.
• C. Decreased case ascertainment – Would generally reduce measured
prevalence.
• D. Elimination of risk factors – Would be expected to reduce incidence over
time.
Question 3
Measures of association
In a cohort study, smokers had a lung cancer incidence of 40 per 1,000 person-years,
while nonsmokers had an incidence of 10 per 1,000 person-years. What is the relative
risk?
A. 0.25
B. 1.0
C. 2.5
D. 4.0
, Correct answer
D. 4.0
Explanation
Relative risk = incidence in exposed ÷ incidence in unexposed = 40 ÷ 10 = 4.0. Smokers
have four times the risk of lung cancer compared with nonsmokers.
Why the other options are incorrect
• A. 0.25 – Inverse of the correct ratio.
• B. 1.0 – Would indicate no association.
• C. 2.5 – Does not match the observed incidence ratio.
Question 4
Absolute risk
Using the data from Question 3, what is the attributable risk (risk difference)
associated with smoking?
A. 10 per 1,000 person-years
B. 20 per 1,000 person-years
C. 30 per 1,000 person-years
D. 40 per 1,000 person-years
Correct answer
C. 30 per 1,000 person-years
Explanation
Attributable risk = incidence in exposed − incidence in unexposed = 40 − 10 = 30 per
1,000 person-years. This represents the excess incidence associated with the
exposure.
Why the other options are incorrect
• A. 10 – Equals the unexposed incidence, not the difference.
• B. 20 – Incorrect subtraction.
• D. 40 – Equals the exposed incidence, not the excess risk.
Authors: David D. Celentano,Moyses Szklo,Youssef Farag
,Gordis Epidemiology, 7th Edition
Chapter 1 Introduction
Question 1
Measures of disease frequency
A city of 500,000 residents reports 2,500 newly diagnosed cases of tuberculosis during
2026. What is the incidence proportion (cumulative incidence) of tuberculosis for that
year?
A. 0.05%
B. 0.5%
C. 5%
D. 50%
Correct answer
B. 0.5%
Explanation
Incidence proportion = new cases ÷ population at risk = 2,500 ÷ 500,000 = 0.005 = 0.5%.
This measure describes the risk of developing disease during a specified period.
Why the other options are incorrect
• A. 0.05% – Tenfold too low; would correspond to 250 cases.
• C. 5% – Tenfold too high; would correspond to 25,000 cases.
• D. 50% – Grossly overestimates risk; would require 250,000 cases.
Question 2
Prevalence vs incidence
,Researchers observe that the prevalence of a chronic neurologic disease has
increased over the past decade while the incidence has remained stable. Which
explanation is most consistent with these findings?
A. Improved survival among affected patients
B. Reduced duration of disease
C. Decreased case ascertainment
D. Elimination of risk factors
Correct answer
A. Improved survival among affected patients
Explanation
Prevalence depends on both incidence and duration. If incidence remains stable but
patients live longer with the disease, prevalence increases because more people are
living with the condition at any given time.
Why the other options are incorrect
• B. Reduced duration of disease – Would tend to decrease prevalence.
• C. Decreased case ascertainment – Would generally reduce measured
prevalence.
• D. Elimination of risk factors – Would be expected to reduce incidence over
time.
Question 3
Measures of association
In a cohort study, smokers had a lung cancer incidence of 40 per 1,000 person-years,
while nonsmokers had an incidence of 10 per 1,000 person-years. What is the relative
risk?
A. 0.25
B. 1.0
C. 2.5
D. 4.0
, Correct answer
D. 4.0
Explanation
Relative risk = incidence in exposed ÷ incidence in unexposed = 40 ÷ 10 = 4.0. Smokers
have four times the risk of lung cancer compared with nonsmokers.
Why the other options are incorrect
• A. 0.25 – Inverse of the correct ratio.
• B. 1.0 – Would indicate no association.
• C. 2.5 – Does not match the observed incidence ratio.
Question 4
Absolute risk
Using the data from Question 3, what is the attributable risk (risk difference)
associated with smoking?
A. 10 per 1,000 person-years
B. 20 per 1,000 person-years
C. 30 per 1,000 person-years
D. 40 per 1,000 person-years
Correct answer
C. 30 per 1,000 person-years
Explanation
Attributable risk = incidence in exposed − incidence in unexposed = 40 − 10 = 30 per
1,000 person-years. This represents the excess incidence associated with the
exposure.
Why the other options are incorrect
• A. 10 – Equals the unexposed incidence, not the difference.
• B. 20 – Incorrect subtraction.
• D. 40 – Equals the exposed incidence, not the excess risk.
