PUBH210 Epidemiology Practice Exam Study Guide Updated 2026 | 300+
Verified Questions and Answers with Detailed Rationales | Measures of
Disease Frequency (Incidence and Prevalence), Study Designs (Cohort,
Case-Control, Cross-Sectional), Outbreak Investigation, Bias and
Confounding, Risk Ratios and Odds Ratios, Screening and Surveillance,
Data Interpretation, Public Health Interventions, Biostatistics Basics |
Complete Exam Prep Resource for Public Health Students Success
Question 1: Which measure of disease frequency represents the proportion of a population
that has a disease at a specific point in time?
A. Incidence rate
B. Cumulative incidence
C. Prevalence
D. Attack rate
CORRECT ANSWER: C. Prevalence
Rationale: Prevalence measures the proportion of individuals in a population who have a
disease or condition at a specific point in time (point prevalence) or during a specified
period (period prevalence). Incidence measures new cases, while prevalence includes
both new and existing cases, making it the appropriate measure for burden of disease at a
given time.
Question 2: In a cohort study investigating the association between smoking and lung
cancer, researchers follow 1,000 smokers and 1,000 non-smokers for 20 years. What is the
primary measure of association that should be calculated?
A. Odds ratio
B. Relative risk
C. Attributable risk percent
D. Population attributable fraction
CORRECT ANSWER: B. Relative risk
Rationale: Cohort studies follow exposed and unexposed groups forward in time to
compare disease incidence, allowing direct calculation of relative risk (risk ratio). The odds
ratio is primarily used in case-control studies where incidence cannot be directly
measured. Relative risk quantifies how many times more likely the exposed group is to
develop the outcome compared to the unexposed group.
**Question 3: A screening test for diabetes has
Thinking completed
Question 1: Which measure of disease frequency represents the proportion of a population
that has a disease at a specific point in time?
A. Incidence rate
B. Cumulative incidence
C. Prevalence
D. Attack rate
,CORRECT ANSWER: C. Prevalence
Rationale: Prevalence measures the proportion of individuals in a population who have a
disease or condition at a specific point in time (point prevalence) or during a specified
period (period prevalence). Incidence measures new cases, while prevalence includes
both new and existing cases, making it the appropriate measure for burden of disease at a
given time.
Question 2: In a cohort study investigating the association between smoking and lung
cancer, researchers follow 1,000 smokers and 1,000 non-smokers for 20 years. What is the
primary measure of association that should be calculated?
A. Odds ratio
B. Relative risk
C. Attributable risk percent
D. Population attributable fraction
CORRECT ANSWER: B. Relative risk
Rationale: Cohort studies follow exposed and unexposed groups forward in time to
compare disease incidence, allowing direct calculation of relative risk (risk ratio). The odds
ratio is primarily used in case-control studies where incidence cannot be directly
measured. Relative risk quantifies how many times more likely the exposed group is to
develop the outcome compared to the unexposed group.
Question 3: A screening test for diabetes has a sensitivity of 90% and a specificity of 85%. If
the prevalence of diabetes in the population is 10%, what is the approximate positive
predictive value?
A. 40%
B. 52%
C. 75%
D. 90%
CORRECT ANSWER: B. 52%
Rationale: Positive predictive value (PPV) depends on sensitivity, specificity, and disease
prevalence. Using a 2x2 table with 1,000 people: 100 have diabetes (prevalence 10%), 900
do not. True positives = 90 (90% of 100), false positives = 135 (15% of 900). PPV = 90/(90+135)
= 90/225 = 40%. Wait, let me recalculate: specificity 85% means 15% false positive rate.
15% of 900 = 135 false positives. True positives = 90% of 100 = 90. PPV = 90/(90+135) =
90/225 = 0.40 = 40%. I need to correct this. Let me adjust the question parameters for
accuracy.
Actually, let me revise this question to ensure numerical accuracy:
Question 3: A screening test for a disease has a sensitivity of 95% and a specificity of 90%.
If the disease prevalence is 5% in a population of 1,000 individuals, approximately how
many true positive results would be expected?
A. 45
B. 48
,C. 90
D. 95
CORRECT ANSWER: B. 48
Rationale: With 5% prevalence in 1,000 people, 50 individuals have the disease. Sensitivity
of 95% means the test correctly identifies 95% of those with disease: 0.95 × 50 = 47.5,
which rounds to approximately 48 true positives. This question tests understanding of how
sensitivity operates on the diseased population to produce true positive results.
Question 4: Which type of bias occurs when the association between exposure and
outcome differs between those who participate in a study and those who do not?
A. Recall bias
B. Observer bias
C. Selection bias
D. Confounding bias
CORRECT ANSWER: C. Selection bias
Rationale: Selection bias arises when the relationship between exposure and disease
differs for those who participate in the study versus those who are eligible but do not
participate. This can distort the measure of association if participation is related to both
exposure and outcome. Recall bias involves differential memory of past exposures,
observer bias involves differential assessment of outcomes, and confounding involves a
third variable associated with both exposure and outcome.
Question 5: The Bradford Hill criterion that assesses whether the exposure precedes the
outcome in time is known as:
A. Strength of association
B. Consistency
C. Temporality
D. Biological gradient
CORRECT ANSWER: C. Temporality
Rationale: Temporality is the only Bradford Hill criterion that is absolutely essential for
causation: the cause must precede the effect in time. Without establishing that exposure
occurred before disease onset, a causal relationship cannot be inferred. Other criteria like
strength, consistency, and biological gradient support causality but are not strictly
required.
Question 6: In a case-control study, the odds ratio is used to estimate the relative risk
under which condition?
A. When the disease is common (>10% prevalence)
B. When the disease is rare (<10% prevalence)
C. When exposure is rare
D. When the study is prospective
CORRECT ANSWER: B. When the disease is rare (<10% prevalence)
, Rationale: The odds ratio approximates the relative risk when the disease outcome is rare
(typically <10% prevalence) in both exposed and unexposed groups. This is known as the
"rare disease assumption." When disease is common, the odds ratio overestimates the
relative risk, making interpretation less intuitive. Case-control studies cannot directly
calculate incidence, so the odds ratio is the primary measure of association.
Question 7: Which study design is most appropriate for investigating the incidence of a
newly emerging infectious disease in a defined population?
A. Cross-sectional study
B. Case-control study
C. Prospective cohort study
D. Ecological study
CORRECT ANSWER: C. Prospective cohort study
Rationale: A prospective cohort study follows a defined population over time to identify
new cases of disease, allowing direct calculation of incidence rates and risk. This design is
ideal for emerging diseases where the goal is to measure how quickly the disease spreads
and identify risk factors. Cross-sectional studies measure prevalence at one time point,
case-control studies start with cases and look backward, and ecological studies use
group-level data.
Question 8: A researcher calculates that the attributable risk of lung cancer due to
smoking is 70 per 1,000 person-years. This means that:
A. 70% of lung cancer cases in smokers are due to smoking
B. 70 additional cases of lung cancer per 1,000 person-years occur among smokers
compared to non-smokers
C. Smokers have a 70 times higher risk of lung cancer
D. Eliminating smoking would prevent 70% of all lung cancer cases
CORRECT ANSWER: B. 70 additional cases of lung cancer per 1,000 person-years occur
among smokers compared to non-smokers
Rationale: Attributable risk (also called risk difference) quantifies the excess incidence of
disease in the exposed group that can be attributed to the exposure. An attributable risk of
70 per 1,000 person-years means that among smokers, there are 70 more cases of lung
cancer per 1,000 person-years of follow-up than would be expected if they had the same
risk as non-smokers. This measure is useful for public health planning and intervention
impact assessment.
Question 9: Which measure is most appropriate for comparing mortality between two
populations with different age distributions?
A. Crude death rate
B. Case fatality rate
C. Age-adjusted mortality rate
D. Proportional mortality ratio
CORRECT ANSWER: C. Age-adjusted mortality rate
Verified Questions and Answers with Detailed Rationales | Measures of
Disease Frequency (Incidence and Prevalence), Study Designs (Cohort,
Case-Control, Cross-Sectional), Outbreak Investigation, Bias and
Confounding, Risk Ratios and Odds Ratios, Screening and Surveillance,
Data Interpretation, Public Health Interventions, Biostatistics Basics |
Complete Exam Prep Resource for Public Health Students Success
Question 1: Which measure of disease frequency represents the proportion of a population
that has a disease at a specific point in time?
A. Incidence rate
B. Cumulative incidence
C. Prevalence
D. Attack rate
CORRECT ANSWER: C. Prevalence
Rationale: Prevalence measures the proportion of individuals in a population who have a
disease or condition at a specific point in time (point prevalence) or during a specified
period (period prevalence). Incidence measures new cases, while prevalence includes
both new and existing cases, making it the appropriate measure for burden of disease at a
given time.
Question 2: In a cohort study investigating the association between smoking and lung
cancer, researchers follow 1,000 smokers and 1,000 non-smokers for 20 years. What is the
primary measure of association that should be calculated?
A. Odds ratio
B. Relative risk
C. Attributable risk percent
D. Population attributable fraction
CORRECT ANSWER: B. Relative risk
Rationale: Cohort studies follow exposed and unexposed groups forward in time to
compare disease incidence, allowing direct calculation of relative risk (risk ratio). The odds
ratio is primarily used in case-control studies where incidence cannot be directly
measured. Relative risk quantifies how many times more likely the exposed group is to
develop the outcome compared to the unexposed group.
**Question 3: A screening test for diabetes has
Thinking completed
Question 1: Which measure of disease frequency represents the proportion of a population
that has a disease at a specific point in time?
A. Incidence rate
B. Cumulative incidence
C. Prevalence
D. Attack rate
,CORRECT ANSWER: C. Prevalence
Rationale: Prevalence measures the proportion of individuals in a population who have a
disease or condition at a specific point in time (point prevalence) or during a specified
period (period prevalence). Incidence measures new cases, while prevalence includes
both new and existing cases, making it the appropriate measure for burden of disease at a
given time.
Question 2: In a cohort study investigating the association between smoking and lung
cancer, researchers follow 1,000 smokers and 1,000 non-smokers for 20 years. What is the
primary measure of association that should be calculated?
A. Odds ratio
B. Relative risk
C. Attributable risk percent
D. Population attributable fraction
CORRECT ANSWER: B. Relative risk
Rationale: Cohort studies follow exposed and unexposed groups forward in time to
compare disease incidence, allowing direct calculation of relative risk (risk ratio). The odds
ratio is primarily used in case-control studies where incidence cannot be directly
measured. Relative risk quantifies how many times more likely the exposed group is to
develop the outcome compared to the unexposed group.
Question 3: A screening test for diabetes has a sensitivity of 90% and a specificity of 85%. If
the prevalence of diabetes in the population is 10%, what is the approximate positive
predictive value?
A. 40%
B. 52%
C. 75%
D. 90%
CORRECT ANSWER: B. 52%
Rationale: Positive predictive value (PPV) depends on sensitivity, specificity, and disease
prevalence. Using a 2x2 table with 1,000 people: 100 have diabetes (prevalence 10%), 900
do not. True positives = 90 (90% of 100), false positives = 135 (15% of 900). PPV = 90/(90+135)
= 90/225 = 40%. Wait, let me recalculate: specificity 85% means 15% false positive rate.
15% of 900 = 135 false positives. True positives = 90% of 100 = 90. PPV = 90/(90+135) =
90/225 = 0.40 = 40%. I need to correct this. Let me adjust the question parameters for
accuracy.
Actually, let me revise this question to ensure numerical accuracy:
Question 3: A screening test for a disease has a sensitivity of 95% and a specificity of 90%.
If the disease prevalence is 5% in a population of 1,000 individuals, approximately how
many true positive results would be expected?
A. 45
B. 48
,C. 90
D. 95
CORRECT ANSWER: B. 48
Rationale: With 5% prevalence in 1,000 people, 50 individuals have the disease. Sensitivity
of 95% means the test correctly identifies 95% of those with disease: 0.95 × 50 = 47.5,
which rounds to approximately 48 true positives. This question tests understanding of how
sensitivity operates on the diseased population to produce true positive results.
Question 4: Which type of bias occurs when the association between exposure and
outcome differs between those who participate in a study and those who do not?
A. Recall bias
B. Observer bias
C. Selection bias
D. Confounding bias
CORRECT ANSWER: C. Selection bias
Rationale: Selection bias arises when the relationship between exposure and disease
differs for those who participate in the study versus those who are eligible but do not
participate. This can distort the measure of association if participation is related to both
exposure and outcome. Recall bias involves differential memory of past exposures,
observer bias involves differential assessment of outcomes, and confounding involves a
third variable associated with both exposure and outcome.
Question 5: The Bradford Hill criterion that assesses whether the exposure precedes the
outcome in time is known as:
A. Strength of association
B. Consistency
C. Temporality
D. Biological gradient
CORRECT ANSWER: C. Temporality
Rationale: Temporality is the only Bradford Hill criterion that is absolutely essential for
causation: the cause must precede the effect in time. Without establishing that exposure
occurred before disease onset, a causal relationship cannot be inferred. Other criteria like
strength, consistency, and biological gradient support causality but are not strictly
required.
Question 6: In a case-control study, the odds ratio is used to estimate the relative risk
under which condition?
A. When the disease is common (>10% prevalence)
B. When the disease is rare (<10% prevalence)
C. When exposure is rare
D. When the study is prospective
CORRECT ANSWER: B. When the disease is rare (<10% prevalence)
, Rationale: The odds ratio approximates the relative risk when the disease outcome is rare
(typically <10% prevalence) in both exposed and unexposed groups. This is known as the
"rare disease assumption." When disease is common, the odds ratio overestimates the
relative risk, making interpretation less intuitive. Case-control studies cannot directly
calculate incidence, so the odds ratio is the primary measure of association.
Question 7: Which study design is most appropriate for investigating the incidence of a
newly emerging infectious disease in a defined population?
A. Cross-sectional study
B. Case-control study
C. Prospective cohort study
D. Ecological study
CORRECT ANSWER: C. Prospective cohort study
Rationale: A prospective cohort study follows a defined population over time to identify
new cases of disease, allowing direct calculation of incidence rates and risk. This design is
ideal for emerging diseases where the goal is to measure how quickly the disease spreads
and identify risk factors. Cross-sectional studies measure prevalence at one time point,
case-control studies start with cases and look backward, and ecological studies use
group-level data.
Question 8: A researcher calculates that the attributable risk of lung cancer due to
smoking is 70 per 1,000 person-years. This means that:
A. 70% of lung cancer cases in smokers are due to smoking
B. 70 additional cases of lung cancer per 1,000 person-years occur among smokers
compared to non-smokers
C. Smokers have a 70 times higher risk of lung cancer
D. Eliminating smoking would prevent 70% of all lung cancer cases
CORRECT ANSWER: B. 70 additional cases of lung cancer per 1,000 person-years occur
among smokers compared to non-smokers
Rationale: Attributable risk (also called risk difference) quantifies the excess incidence of
disease in the exposed group that can be attributed to the exposure. An attributable risk of
70 per 1,000 person-years means that among smokers, there are 70 more cases of lung
cancer per 1,000 person-years of follow-up than would be expected if they had the same
risk as non-smokers. This measure is useful for public health planning and intervention
impact assessment.
Question 9: Which measure is most appropriate for comparing mortality between two
populations with different age distributions?
A. Crude death rate
B. Case fatality rate
C. Age-adjusted mortality rate
D. Proportional mortality ratio
CORRECT ANSWER: C. Age-adjusted mortality rate
