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 5,000 adults, 150 new cases of hypertension are identified during
2025. The total person-time of observation is 4,750 person-years. What is the incidence
rate (per 1,000 person-years)?
A. 15.8
B. 31.6
C. 7.5
D. 30.0
Correct Answer: B
Rationale: Incidence rate = (new cases / total person-time) × 1,000 = (,750) ×
1,000 ≈ 31.6 per 1,000 person-years. Option A incorrectly divides by 5,000 (total
cohort), option C forgets the multiplier, and option D mis-uses total population as
denominator.
,Q2: Which pair of indicators best distinguishes the "force" of a disease from its "burden"
in a population?
A. Incidence vs. prevalence
B. Sensitivity vs. specificity
C. Attack rate vs. case-fatality rate
D. Odds ratio vs. risk ratio
Correct Answer: A
Rationale: Incidence quantifies new events (force), while prevalence quantifies existing
cases (burden). Sensitivity/specificity evaluate tests, attack/case-fatality rates measure
outbreak intensity/fatality, and odds/risk ratios compare exposures.
Q3: A point-source outbreak of gastroenteritis occurs at a conference. Epidemiologists
calculate an "attack rate." The correct formula is:
A. (Existing cases / Total population) × 1,000
B. (New cases during follow-up / Population at start) × 100
C. (Ill persons / Total persons exposed) × 100
D. (Deaths / Total cases) × 100
Correct Answer: C
, Rationale: Attack rate = (ill among exposed / total exposed) × 100; used for short,
defined-risk periods. A describes prevalence, B incidence proportion, and D
case-fatality rate.
Q4: In a cross-sectional survey, 120 persons are found hypertensive out of 1,200
screened. This proportion is best described as:
A. Incidence
B. Prevalence
C. Cumulative incidence
D. Incidence density
Correct Answer: B
Rationale: A single-time snapshot yields prevalence (existing cases). Incidence requires
follow-up time; cumulative incidence is a proportion over time; incidence density uses
person-time.
Q5: The case-fatality rate of a disease is 5 %. This means:
A. 5 % of the entire population dies from the disease
B. Among diagnosed cases, 5 % die from the disease
C. 5 % of exposed persons become cases
Population Health Epidemiology & Biostatistics | Questions
with Verified Answers | 100% Correct | Pass Guaranteed
SECTION 1: Epidemiological Concepts & Measures
Q1: In a cohort of 5,000 adults, 150 new cases of hypertension are identified during
2025. The total person-time of observation is 4,750 person-years. What is the incidence
rate (per 1,000 person-years)?
A. 15.8
B. 31.6
C. 7.5
D. 30.0
Correct Answer: B
Rationale: Incidence rate = (new cases / total person-time) × 1,000 = (,750) ×
1,000 ≈ 31.6 per 1,000 person-years. Option A incorrectly divides by 5,000 (total
cohort), option C forgets the multiplier, and option D mis-uses total population as
denominator.
,Q2: Which pair of indicators best distinguishes the "force" of a disease from its "burden"
in a population?
A. Incidence vs. prevalence
B. Sensitivity vs. specificity
C. Attack rate vs. case-fatality rate
D. Odds ratio vs. risk ratio
Correct Answer: A
Rationale: Incidence quantifies new events (force), while prevalence quantifies existing
cases (burden). Sensitivity/specificity evaluate tests, attack/case-fatality rates measure
outbreak intensity/fatality, and odds/risk ratios compare exposures.
Q3: A point-source outbreak of gastroenteritis occurs at a conference. Epidemiologists
calculate an "attack rate." The correct formula is:
A. (Existing cases / Total population) × 1,000
B. (New cases during follow-up / Population at start) × 100
C. (Ill persons / Total persons exposed) × 100
D. (Deaths / Total cases) × 100
Correct Answer: C
, Rationale: Attack rate = (ill among exposed / total exposed) × 100; used for short,
defined-risk periods. A describes prevalence, B incidence proportion, and D
case-fatality rate.
Q4: In a cross-sectional survey, 120 persons are found hypertensive out of 1,200
screened. This proportion is best described as:
A. Incidence
B. Prevalence
C. Cumulative incidence
D. Incidence density
Correct Answer: B
Rationale: A single-time snapshot yields prevalence (existing cases). Incidence requires
follow-up time; cumulative incidence is a proportion over time; incidence density uses
person-time.
Q5: The case-fatality rate of a disease is 5 %. This means:
A. 5 % of the entire population dies from the disease
B. Among diagnosed cases, 5 % die from the disease
C. 5 % of exposed persons become cases
