1|Page
NR 503 MIDTERM EXAM 2025-2026 | 240 VERIFIED QUESTIONS
AND 100% CORRECT ANSWERS WITH DETAILED
RATIONALES | PUBLIC HEALTH, EPIDEMIOLOGY &
POPULATION HEALTH STUDY GUIDE
Q1. Which measure best describes the occurrence of new cases of disease in
a defined population during a specific time?
A. Prevalence
B. Incidence
C. Mortality rate
D. Case-fatality ratio
Answer: B. Incidence
Rationale: Incidence reflects new cases within a population during a set
time, while prevalence includes both old and new cases.
Q2. The number of people living with diabetes in a community at a given
time represents:
A. Incidence rate
B. Prevalence rate
C. Mortality rate
D. Risk ratio
Answer: B. Prevalence rate
Rationale: Prevalence measures the burden of disease, including both
existing and new cases.
Q3. In epidemiology, which type of study design is most useful for
identifying risk factors for rare diseases?
A. Cross-sectional study
B. Case-control study
C. Cohort study
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D. Randomized controlled trial
Answer: B. Case-control study
Rationale: Case-control studies are efficient for studying rare diseases by
comparing those with the disease (cases) to those without (controls).
Q4. A community has 200 new flu cases in January. The population is
10,000. What is the incidence rate?
A. 0.2%
B. 2%
C. 20%
D. 10%
Answer: B. 2%
Rationale: Incidence rate = (200 ÷ 10,000) × 100 = 2%.
Q5. The epidemiologic triangle includes:
A. Host, agent, environment
B. Agent, outcome, community
C. Person, place, time
D. Risk, prevention, control
Answer: A. Host, agent, environment
Rationale: The classic model explains disease occurrence as interaction
among these three components.
Q6. Herd immunity occurs when:
A. All individuals are vaccinated
B. A critical proportion of the population is immune
C. Disease eradication has been achieved
D. Only children are vaccinated
Answer: B. A critical proportion of the population is immune
Rationale: Herd immunity protects even non-immune individuals when
enough people are resistant to transmission.
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Q7. Which type of bias occurs when participants with certain characteristics
are more likely to be included in a study?
A. Recall bias
B. Selection bias
C. Observer bias
D. Information bias
Answer: B. Selection bias
Rationale: Selection bias occurs when study participants are not
representative of the population.
Q8. Relative risk is best calculated in which type of study design?
A. Case-control study
B. Cohort study
C. Cross-sectional study
D. Qualitative study
Answer: B. Cohort study
Rationale: Cohort studies follow exposed and unexposed groups to calculate
relative risk.
Q9. Odds ratio is most appropriate in:
A. Cohort studies
B. Case-control studies
C. Ecological studies
D. Clinical trials
Answer: B. Case-control studies
Rationale: Case-control studies measure association using odds ratios since
incidence cannot be directly measured.
Q10. The natural history of disease model includes:
A. Exposure, diagnosis, recovery
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B. Susceptibility, subclinical disease, clinical disease, outcome
C. Primary, secondary, tertiary prevention
D. Screening, treatment, cure
Answer: B. Susceptibility, subclinical disease, clinical disease, outcome
Rationale: This model illustrates disease progression over time.
Q11. The purpose of primary prevention is to:
A. Reduce complications of established disease
B. Prevent disease occurrence
C. Detect disease early
D. Prolong survival after diagnosis
Answer: B. Prevent disease occurrence
Rationale: Primary prevention aims to prevent disease before it begins (e.g.,
vaccination, education).
Q12. Mammography screening for breast cancer is an example of:
A. Primary prevention
B. Secondary prevention
C. Tertiary prevention
D. Palliative care
Answer: B. Secondary prevention
Rationale: Screening detects disease early, before symptoms progress.
Q13. The most accurate measure of a screening test’s ability to detect
disease when it is truly present is:
A. Specificity
B. Sensitivity
C. Predictive value positive
D. Predictive value negative
Answer: B. Sensitivity
NR 503 MIDTERM EXAM 2025-2026 | 240 VERIFIED QUESTIONS
AND 100% CORRECT ANSWERS WITH DETAILED
RATIONALES | PUBLIC HEALTH, EPIDEMIOLOGY &
POPULATION HEALTH STUDY GUIDE
Q1. Which measure best describes the occurrence of new cases of disease in
a defined population during a specific time?
A. Prevalence
B. Incidence
C. Mortality rate
D. Case-fatality ratio
Answer: B. Incidence
Rationale: Incidence reflects new cases within a population during a set
time, while prevalence includes both old and new cases.
Q2. The number of people living with diabetes in a community at a given
time represents:
A. Incidence rate
B. Prevalence rate
C. Mortality rate
D. Risk ratio
Answer: B. Prevalence rate
Rationale: Prevalence measures the burden of disease, including both
existing and new cases.
Q3. In epidemiology, which type of study design is most useful for
identifying risk factors for rare diseases?
A. Cross-sectional study
B. Case-control study
C. Cohort study
,2|Page
D. Randomized controlled trial
Answer: B. Case-control study
Rationale: Case-control studies are efficient for studying rare diseases by
comparing those with the disease (cases) to those without (controls).
Q4. A community has 200 new flu cases in January. The population is
10,000. What is the incidence rate?
A. 0.2%
B. 2%
C. 20%
D. 10%
Answer: B. 2%
Rationale: Incidence rate = (200 ÷ 10,000) × 100 = 2%.
Q5. The epidemiologic triangle includes:
A. Host, agent, environment
B. Agent, outcome, community
C. Person, place, time
D. Risk, prevention, control
Answer: A. Host, agent, environment
Rationale: The classic model explains disease occurrence as interaction
among these three components.
Q6. Herd immunity occurs when:
A. All individuals are vaccinated
B. A critical proportion of the population is immune
C. Disease eradication has been achieved
D. Only children are vaccinated
Answer: B. A critical proportion of the population is immune
Rationale: Herd immunity protects even non-immune individuals when
enough people are resistant to transmission.
,3|Page
Q7. Which type of bias occurs when participants with certain characteristics
are more likely to be included in a study?
A. Recall bias
B. Selection bias
C. Observer bias
D. Information bias
Answer: B. Selection bias
Rationale: Selection bias occurs when study participants are not
representative of the population.
Q8. Relative risk is best calculated in which type of study design?
A. Case-control study
B. Cohort study
C. Cross-sectional study
D. Qualitative study
Answer: B. Cohort study
Rationale: Cohort studies follow exposed and unexposed groups to calculate
relative risk.
Q9. Odds ratio is most appropriate in:
A. Cohort studies
B. Case-control studies
C. Ecological studies
D. Clinical trials
Answer: B. Case-control studies
Rationale: Case-control studies measure association using odds ratios since
incidence cannot be directly measured.
Q10. The natural history of disease model includes:
A. Exposure, diagnosis, recovery
, 4|Page
B. Susceptibility, subclinical disease, clinical disease, outcome
C. Primary, secondary, tertiary prevention
D. Screening, treatment, cure
Answer: B. Susceptibility, subclinical disease, clinical disease, outcome
Rationale: This model illustrates disease progression over time.
Q11. The purpose of primary prevention is to:
A. Reduce complications of established disease
B. Prevent disease occurrence
C. Detect disease early
D. Prolong survival after diagnosis
Answer: B. Prevent disease occurrence
Rationale: Primary prevention aims to prevent disease before it begins (e.g.,
vaccination, education).
Q12. Mammography screening for breast cancer is an example of:
A. Primary prevention
B. Secondary prevention
C. Tertiary prevention
D. Palliative care
Answer: B. Secondary prevention
Rationale: Screening detects disease early, before symptoms progress.
Q13. The most accurate measure of a screening test’s ability to detect
disease when it is truly present is:
A. Specificity
B. Sensitivity
C. Predictive value positive
D. Predictive value negative
Answer: B. Sensitivity
