NR 503 / NR503 Midterm Exam Actual Exam 2026 |
Population Health Epidemiology & Biostatistics | Questions
with Verified Answers | 100% Correct | Pass Guaranteed
SECTION 1: Epidemiological Concepts & Measures
Q1: In a cohort of 2,000 healthy adults, 80 new cases of hypertension are identified over
12 months. What is the cumulative incidence per 1,000 population?
A. 20
B. 40
C. 60
D. 80
Correct Answer: B
Rationale: Cumulative incidence = (new cases / population at risk) × 1,000 = (,000)
× 1,000 = 40 per 1,000. Option A halves the correct rate, C uses total population instead
of at-risk, and D forgets to multiply by 1,000.
Q2: Which measure best expresses the probability that a healthy individual will develop
a disease during a specified period?
A. Point prevalence
B. Incidence rate
,C. Period prevalence
D. Attack rate
Correct Answer: B
Rationale: Incidence rate quantifies new-disease occurrence over person-time. Point
prevalence (A) is a snapshot of existing disease, period prevalence (C) covers a span
but includes pre-existing cases, and attack rate (D) is a cumulative incidence used in
outbreaks, not general probability.
Q3: A county’s adult smoking prevalence is 18 % in 2024 and 15 % in 2025. Which term
describes this change?
A. Secular trend
B. Birth-cohort effect
C. Regression to the mean
D. Hawthorne effect
Correct Answer: A
Rationale: A secular trend is a gradual population-level shift over time. A birth-cohort
effect (B) compares generations, regression to the mean (C) is a statistical artifact, and
the Hawthorne effect (D) refers to behavior changes from being observed.
Q4: In a two-by-two table, the calculated risk ratio (RR) is 0.75. This is interpreted as:
A. 75 % increased risk in the exposed group
B. 25 % reduced risk in the exposed group
, C. No association between exposure and outcome
D. 75 % reduced risk in the unexposed group
Correct Answer: B
Rationale: RR = 0.75 implies the exposed group has 25 % lower risk than the unexposed
(1 – 0.75 = 0.25). Option A misreads 0.75 as increased, C applies to RR = 1, and D
reverses the comparison direction.
Q5: Which of the following is a proportion (unitless)?
A. Incidence rate (per 1,000 py)
B. Cumulative incidence (%)
C. Person-years of follow-up
D. Age-adjusted rate
Correct Answer: B
Rationale: Cumulative incidence is a proportion (cases / population) with no time unit.
Incidence rate (A) and age-adjusted rate (D) include person-time, while person-years (C)
is a denominator, not a proportion.
Q6: A point-source outbreak epidemic curve typically appears:
A. Irregularly scattered over months
B. As a sharp peak with a rapid return to baseline
C. As a gradual rise over several incubation periods
D. Bimodal with equal-sized peaks
Population Health Epidemiology & Biostatistics | Questions
with Verified Answers | 100% Correct | Pass Guaranteed
SECTION 1: Epidemiological Concepts & Measures
Q1: In a cohort of 2,000 healthy adults, 80 new cases of hypertension are identified over
12 months. What is the cumulative incidence per 1,000 population?
A. 20
B. 40
C. 60
D. 80
Correct Answer: B
Rationale: Cumulative incidence = (new cases / population at risk) × 1,000 = (,000)
× 1,000 = 40 per 1,000. Option A halves the correct rate, C uses total population instead
of at-risk, and D forgets to multiply by 1,000.
Q2: Which measure best expresses the probability that a healthy individual will develop
a disease during a specified period?
A. Point prevalence
B. Incidence rate
,C. Period prevalence
D. Attack rate
Correct Answer: B
Rationale: Incidence rate quantifies new-disease occurrence over person-time. Point
prevalence (A) is a snapshot of existing disease, period prevalence (C) covers a span
but includes pre-existing cases, and attack rate (D) is a cumulative incidence used in
outbreaks, not general probability.
Q3: A county’s adult smoking prevalence is 18 % in 2024 and 15 % in 2025. Which term
describes this change?
A. Secular trend
B. Birth-cohort effect
C. Regression to the mean
D. Hawthorne effect
Correct Answer: A
Rationale: A secular trend is a gradual population-level shift over time. A birth-cohort
effect (B) compares generations, regression to the mean (C) is a statistical artifact, and
the Hawthorne effect (D) refers to behavior changes from being observed.
Q4: In a two-by-two table, the calculated risk ratio (RR) is 0.75. This is interpreted as:
A. 75 % increased risk in the exposed group
B. 25 % reduced risk in the exposed group
, C. No association between exposure and outcome
D. 75 % reduced risk in the unexposed group
Correct Answer: B
Rationale: RR = 0.75 implies the exposed group has 25 % lower risk than the unexposed
(1 – 0.75 = 0.25). Option A misreads 0.75 as increased, C applies to RR = 1, and D
reverses the comparison direction.
Q5: Which of the following is a proportion (unitless)?
A. Incidence rate (per 1,000 py)
B. Cumulative incidence (%)
C. Person-years of follow-up
D. Age-adjusted rate
Correct Answer: B
Rationale: Cumulative incidence is a proportion (cases / population) with no time unit.
Incidence rate (A) and age-adjusted rate (D) include person-time, while person-years (C)
is a denominator, not a proportion.
Q6: A point-source outbreak epidemic curve typically appears:
A. Irregularly scattered over months
B. As a sharp peak with a rapid return to baseline
C. As a gradual rise over several incubation periods
D. Bimodal with equal-sized peaks
