PUBH210 Epidemiology Exam Prep – Real Practice Questions, Answers &
Detailed Rationales (Updated 2026) | Disease Patterns &
Transmission, Outbreak Investigation, Incidence & Prevalence
Calculations, Cohort & Case-Control Studies, Public Health Surveillance,
Risk Factors & Bias, Screening Methods, Biostatistics Foundations,
Population Health & Data Analysis
Question 1: What is the primary distinction between incidence proportion and
prevalence in epidemiological measurement?
A. Incidence proportion measures all existing cases, while prevalence measures only
new cases
B. Incidence proportion quantifies new cases over time among those at risk, while
prevalence quantifies all existing cases at a point or period in time
C. Incidence proportion is expressed as a rate per person-time, while prevalence is
always a simple count
D. Incidence proportion applies only to infectious diseases, while prevalence applies
only to chronic conditions
CORRECT ANSWER: B. Incidence proportion quantifies new cases over time among
those at risk, while prevalence quantifies all existing cases at a point or period in
time
Rationale: Incidence proportion (cumulative incidence) measures the risk of developing
a disease by counting new cases among a population at risk during a defined period.
Prevalence measures the burden of disease by counting all existing cases (new and pre-
existing) at a specific point or over a period. Option A reverses the definitions, Option C
incorrectly characterizes incidence proportion (which is a proportion, not a person-time
rate), and Option D incorrectly limits the application of these measures to specific
disease types.
Question 2: In a cohort study investigating the association between smoking and
lung cancer, researchers follow 10,000 smokers and 10,000 non-smokers for 20
years. Which measure of association is most appropriate to calculate from this
study design?
A. Odds ratio
B. Prevalence ratio
C. Risk ratio (relative risk)
D. Attributable fraction in the population
CORRECT ANSWER: C. Risk ratio (relative risk)
Rationale: Cohort studies follow exposed and unexposed groups forward in time to
observe disease occurrence, allowing direct calculation of incidence in each group. The
risk ratio (relative risk) compares the incidence of disease in the exposed group to the
incidence in the unexposed group, making it the most appropriate measure of
association for cohort studies. Odds ratios are typically used in case-control studies
,PUBH210 Epidemiology Exam Prep – Real Practice Questions, Answers &
Detailed Rationales (Updated 2026) | Disease Patterns &
Transmission, Outbreak Investigation, Incidence & Prevalence
Calculations, Cohort & Case-Control Studies, Public Health Surveillance,
Risk Factors & Bias, Screening Methods, Biostatistics Foundations,
Population Health & Data Analysis
where incidence cannot be directly calculated. Prevalence ratios are used in cross-
sectional studies, and attributable fraction requires additional population-level data.
Question 3: A screening test for a rare disease has high sensitivity but low
specificity. What is the most likely consequence of using this test in a general
population with low disease prevalence?
A. Most positive test results will be true positives
B. The positive predictive value will be low
C. The negative predictive value will be low
D. The test will miss most cases of the disease
CORRECT ANSWER: B. The positive predictive value will be low
Rationale: Positive predictive value (PPV) is the probability that a person with a positive
test result truly has the disease. PPV depends on sensitivity, specificity, and disease
prevalence. When prevalence is low, even a test with high sensitivity and moderate
specificity will yield many false positives relative to true positives, resulting in low PPV.
High sensitivity ensures few false negatives (so Option D is incorrect), and negative
predictive value tends to be high when prevalence is low (making Option C incorrect).
Option A is incorrect because low specificity in a low-prevalence setting produces many
false positives.
Question 4: Which of the following best describes confounding in epidemiological
research?
A. A systematic error in the design or conduct of a study that leads to an incorrect
estimate of association
B. A distortion of the exposure-outcome association due to a third variable associated
with both exposure and outcome, but not on the causal pathway
C. The modification of an exposure effect by a third variable, resulting in different effect
estimates across subgroups
D. Random variation in study results due to sampling error
CORRECT ANSWER: B. A distortion of the exposure-outcome association due to a
third variable associated with both exposure and outcome, but not on the causal
pathway
Rationale: Confounding occurs when a third variable (confounder) is associated with
both the exposure and the outcome and is not an intermediate step in the causal
pathway. This creates a spurious association or distorts the true exposure-outcome
,PUBH210 Epidemiology Exam Prep – Real Practice Questions, Answers &
Detailed Rationales (Updated 2026) | Disease Patterns &
Transmission, Outbreak Investigation, Incidence & Prevalence
Calculations, Cohort & Case-Control Studies, Public Health Surveillance,
Risk Factors & Bias, Screening Methods, Biostatistics Foundations,
Population Health & Data Analysis
relationship. Option A describes bias broadly, Option C describes effect modification
(interaction), and Option D describes random error, not confounding.
Question 5: In a case-control study, the odds ratio is calculated as 3.5 with a 95%
confidence interval of 1.8 to 6.9. How should this result be interpreted?
A. The exposure causes the disease with 95% certainty
B. Cases were 3.5 times more likely to have been exposed than controls, and the
association is statistically significant at the 0.05 level
C. The risk of disease is 3.5 times higher in the exposed group
D. There is no association between exposure and disease because the confidence
interval includes values close to 1
CORRECT ANSWER: B. Cases were 3.5 times more likely to have been exposed than
controls, and the association is statistically significant at the 0.05 level
Rationale: In case-control studies, the odds ratio approximates the relative risk when
the disease is rare. An OR of 3.5 indicates that cases had 3.5 times the odds of exposure
compared to controls. The 95% CI (1.8–6.9) does not include 1.0, indicating statistical
significance at α=0.05. Option A incorrectly implies causation from an observational
measure. Option C misinterprets the OR as a risk ratio (which cannot be directly
calculated in case-control studies). Option D is incorrect because the CI does not
include 1.0.
Question 6: Which Bradford Hill criterion is best illustrated by the observation that
higher doses of a chemical exposure are associated with progressively higher risk
of disease?
A. Strength of association
B. Consistency
C. Biological gradient (dose-response)
D. Temporality
CORRECT ANSWER: C. Biological gradient (dose-response)
Rationale: The biological gradient criterion refers to a dose-response relationship,
where increasing levels of exposure correspond to increasing risk of the outcome. This
pattern strengthens the argument for a causal relationship. Strength of association
refers to the magnitude of the measure of association. Consistency refers to replication
of findings across different studies and settings. Temporality requires that exposure
precedes outcome, which is necessary but not demonstrated by dose-response alone.
, PUBH210 Epidemiology Exam Prep – Real Practice Questions, Answers &
Detailed Rationales (Updated 2026) | Disease Patterns &
Transmission, Outbreak Investigation, Incidence & Prevalence
Calculations, Cohort & Case-Control Studies, Public Health Surveillance,
Risk Factors & Bias, Screening Methods, Biostatistics Foundations,
Population Health & Data Analysis
Question 7: During an outbreak investigation, the epidemic curve shows a sharp
peak followed by a rapid decline in cases over a 3-day period. What type of
outbreak pattern does this most likely represent?
A. Point source outbreak
B. Propagated outbreak
C. Continuous common source outbreak
D. Intermittent common source outbreak
CORRECT ANSWER: A. Point source outbreak
Rationale: A point source outbreak occurs when individuals are exposed to a common
harmful agent over a brief, well-defined period. The epidemic curve typically shows a
rapid rise and fall in cases, with most cases occurring within one incubation period of
the disease. Propagated outbreaks show successive waves of cases due to person-to-
person transmission. Continuous common source outbreaks show a plateau of cases
over time, while intermittent sources show irregular peaks.
Question 8: What is the primary purpose of age standardization when comparing
disease rates between two populations?
A. To eliminate all sources of bias in rate comparison
B. To adjust for differences in age distribution so that rates reflect true differences in risk
rather than demographic structure
C. To increase the statistical power of the comparison
D. To convert incidence rates into prevalence estimates
CORRECT ANSWER: B. To adjust for differences in age distribution so that rates
reflect true differences in risk rather than demographic structure
Rationale: Age standardization (direct or indirect) adjusts crude rates to account for
differences in age composition between populations. Since many diseases have age-
specific risks, comparing crude rates between populations with different age structures
can be misleading. Standardization allows for fairer comparisons by applying age-
specific rates to a standard population. It does not eliminate all bias (Option A), does
not inherently increase statistical power (Option C), and does not convert incidence to
prevalence (Option D).
Question 9: In a randomized controlled trial, participants are assigned to
intervention or control groups using computer-generated random numbers. What
type of bias is primarily minimized by this procedure?
Detailed Rationales (Updated 2026) | Disease Patterns &
Transmission, Outbreak Investigation, Incidence & Prevalence
Calculations, Cohort & Case-Control Studies, Public Health Surveillance,
Risk Factors & Bias, Screening Methods, Biostatistics Foundations,
Population Health & Data Analysis
Question 1: What is the primary distinction between incidence proportion and
prevalence in epidemiological measurement?
A. Incidence proportion measures all existing cases, while prevalence measures only
new cases
B. Incidence proportion quantifies new cases over time among those at risk, while
prevalence quantifies all existing cases at a point or period in time
C. Incidence proportion is expressed as a rate per person-time, while prevalence is
always a simple count
D. Incidence proportion applies only to infectious diseases, while prevalence applies
only to chronic conditions
CORRECT ANSWER: B. Incidence proportion quantifies new cases over time among
those at risk, while prevalence quantifies all existing cases at a point or period in
time
Rationale: Incidence proportion (cumulative incidence) measures the risk of developing
a disease by counting new cases among a population at risk during a defined period.
Prevalence measures the burden of disease by counting all existing cases (new and pre-
existing) at a specific point or over a period. Option A reverses the definitions, Option C
incorrectly characterizes incidence proportion (which is a proportion, not a person-time
rate), and Option D incorrectly limits the application of these measures to specific
disease types.
Question 2: In a cohort study investigating the association between smoking and
lung cancer, researchers follow 10,000 smokers and 10,000 non-smokers for 20
years. Which measure of association is most appropriate to calculate from this
study design?
A. Odds ratio
B. Prevalence ratio
C. Risk ratio (relative risk)
D. Attributable fraction in the population
CORRECT ANSWER: C. Risk ratio (relative risk)
Rationale: Cohort studies follow exposed and unexposed groups forward in time to
observe disease occurrence, allowing direct calculation of incidence in each group. The
risk ratio (relative risk) compares the incidence of disease in the exposed group to the
incidence in the unexposed group, making it the most appropriate measure of
association for cohort studies. Odds ratios are typically used in case-control studies
,PUBH210 Epidemiology Exam Prep – Real Practice Questions, Answers &
Detailed Rationales (Updated 2026) | Disease Patterns &
Transmission, Outbreak Investigation, Incidence & Prevalence
Calculations, Cohort & Case-Control Studies, Public Health Surveillance,
Risk Factors & Bias, Screening Methods, Biostatistics Foundations,
Population Health & Data Analysis
where incidence cannot be directly calculated. Prevalence ratios are used in cross-
sectional studies, and attributable fraction requires additional population-level data.
Question 3: A screening test for a rare disease has high sensitivity but low
specificity. What is the most likely consequence of using this test in a general
population with low disease prevalence?
A. Most positive test results will be true positives
B. The positive predictive value will be low
C. The negative predictive value will be low
D. The test will miss most cases of the disease
CORRECT ANSWER: B. The positive predictive value will be low
Rationale: Positive predictive value (PPV) is the probability that a person with a positive
test result truly has the disease. PPV depends on sensitivity, specificity, and disease
prevalence. When prevalence is low, even a test with high sensitivity and moderate
specificity will yield many false positives relative to true positives, resulting in low PPV.
High sensitivity ensures few false negatives (so Option D is incorrect), and negative
predictive value tends to be high when prevalence is low (making Option C incorrect).
Option A is incorrect because low specificity in a low-prevalence setting produces many
false positives.
Question 4: Which of the following best describes confounding in epidemiological
research?
A. A systematic error in the design or conduct of a study that leads to an incorrect
estimate of association
B. A distortion of the exposure-outcome association due to a third variable associated
with both exposure and outcome, but not on the causal pathway
C. The modification of an exposure effect by a third variable, resulting in different effect
estimates across subgroups
D. Random variation in study results due to sampling error
CORRECT ANSWER: B. A distortion of the exposure-outcome association due to a
third variable associated with both exposure and outcome, but not on the causal
pathway
Rationale: Confounding occurs when a third variable (confounder) is associated with
both the exposure and the outcome and is not an intermediate step in the causal
pathway. This creates a spurious association or distorts the true exposure-outcome
,PUBH210 Epidemiology Exam Prep – Real Practice Questions, Answers &
Detailed Rationales (Updated 2026) | Disease Patterns &
Transmission, Outbreak Investigation, Incidence & Prevalence
Calculations, Cohort & Case-Control Studies, Public Health Surveillance,
Risk Factors & Bias, Screening Methods, Biostatistics Foundations,
Population Health & Data Analysis
relationship. Option A describes bias broadly, Option C describes effect modification
(interaction), and Option D describes random error, not confounding.
Question 5: In a case-control study, the odds ratio is calculated as 3.5 with a 95%
confidence interval of 1.8 to 6.9. How should this result be interpreted?
A. The exposure causes the disease with 95% certainty
B. Cases were 3.5 times more likely to have been exposed than controls, and the
association is statistically significant at the 0.05 level
C. The risk of disease is 3.5 times higher in the exposed group
D. There is no association between exposure and disease because the confidence
interval includes values close to 1
CORRECT ANSWER: B. Cases were 3.5 times more likely to have been exposed than
controls, and the association is statistically significant at the 0.05 level
Rationale: In case-control studies, the odds ratio approximates the relative risk when
the disease is rare. An OR of 3.5 indicates that cases had 3.5 times the odds of exposure
compared to controls. The 95% CI (1.8–6.9) does not include 1.0, indicating statistical
significance at α=0.05. Option A incorrectly implies causation from an observational
measure. Option C misinterprets the OR as a risk ratio (which cannot be directly
calculated in case-control studies). Option D is incorrect because the CI does not
include 1.0.
Question 6: Which Bradford Hill criterion is best illustrated by the observation that
higher doses of a chemical exposure are associated with progressively higher risk
of disease?
A. Strength of association
B. Consistency
C. Biological gradient (dose-response)
D. Temporality
CORRECT ANSWER: C. Biological gradient (dose-response)
Rationale: The biological gradient criterion refers to a dose-response relationship,
where increasing levels of exposure correspond to increasing risk of the outcome. This
pattern strengthens the argument for a causal relationship. Strength of association
refers to the magnitude of the measure of association. Consistency refers to replication
of findings across different studies and settings. Temporality requires that exposure
precedes outcome, which is necessary but not demonstrated by dose-response alone.
, PUBH210 Epidemiology Exam Prep – Real Practice Questions, Answers &
Detailed Rationales (Updated 2026) | Disease Patterns &
Transmission, Outbreak Investigation, Incidence & Prevalence
Calculations, Cohort & Case-Control Studies, Public Health Surveillance,
Risk Factors & Bias, Screening Methods, Biostatistics Foundations,
Population Health & Data Analysis
Question 7: During an outbreak investigation, the epidemic curve shows a sharp
peak followed by a rapid decline in cases over a 3-day period. What type of
outbreak pattern does this most likely represent?
A. Point source outbreak
B. Propagated outbreak
C. Continuous common source outbreak
D. Intermittent common source outbreak
CORRECT ANSWER: A. Point source outbreak
Rationale: A point source outbreak occurs when individuals are exposed to a common
harmful agent over a brief, well-defined period. The epidemic curve typically shows a
rapid rise and fall in cases, with most cases occurring within one incubation period of
the disease. Propagated outbreaks show successive waves of cases due to person-to-
person transmission. Continuous common source outbreaks show a plateau of cases
over time, while intermittent sources show irregular peaks.
Question 8: What is the primary purpose of age standardization when comparing
disease rates between two populations?
A. To eliminate all sources of bias in rate comparison
B. To adjust for differences in age distribution so that rates reflect true differences in risk
rather than demographic structure
C. To increase the statistical power of the comparison
D. To convert incidence rates into prevalence estimates
CORRECT ANSWER: B. To adjust for differences in age distribution so that rates
reflect true differences in risk rather than demographic structure
Rationale: Age standardization (direct or indirect) adjusts crude rates to account for
differences in age composition between populations. Since many diseases have age-
specific risks, comparing crude rates between populations with different age structures
can be misleading. Standardization allows for fairer comparisons by applying age-
specific rates to a standard population. It does not eliminate all bias (Option A), does
not inherently increase statistical power (Option C), and does not convert incidence to
prevalence (Option D).
Question 9: In a randomized controlled trial, participants are assigned to
intervention or control groups using computer-generated random numbers. What
type of bias is primarily minimized by this procedure?
