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MFPHMI Part I study materials
MFPHMI Part I study resources

MFPHMI Part I practice questions

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Question 1Epidemiology

Which measure of disease frequency is defined as the number of new cases occurring in a population at risk during a specified time period, divided by the person-time at risk?

  1. Attack rate
  2. Incidence rate Correct answer.
  3. Case fatality
  4. Point prevalence

Explanation

An incidence rate uses person-time in the denominator to express the speed at which new cases arise. It requires a defined population at risk and a defined follow-up period.

Question 2Epidemiology

A screening survey finds 400 people with hypertension among 10,000 adults. Which term best describes the value 400/10,000?

  1. Mortality rate
  2. Relative risk
  3. Prevalence proportion Correct answer.
  4. Incidence rate

Explanation

Prevalence proportion counts all existing cases in the population at one point in time divided by the total population. No follow-up or person-time is involved.

Question 3Epidemiology

Which study design is most appropriate for estimating incidence and establishing temporal sequence between exposure and outcome?

  1. Ecologic correlation study
  2. Prospective cohort study Correct answer.
  3. Cross-sectional survey
  4. Case-control study

Explanation

A prospective cohort follows people free of outcome over time, so new cases and their timing relative to exposure can be measured directly. This establishes temporality.

Question 4Epidemiology

In a case-control study of lung cancer, 200 cases and 200 controls are enrolled. Which measure of association is calculated?

  1. Risk ratio
  2. Odds ratio Correct answer.
  3. Incidence rate ratio
  4. Attributable risk percent

Explanation

Case-control studies sample on outcome status, so the odds ratio is the appropriate measure of association. Risk and incidence cannot be estimated directly from such sampling.

Question 5Epidemiology

A test has sensitivity of 90% and specificity of 95%. In a population with low disease prevalence, which property of the test changes most?

  1. Specificity
  2. Positive predictive value Correct answer.
  3. Negative likelihood ratio
  4. Sensitivity

Explanation

Predictive values depend on prevalence, so a low prevalence sharply reduces positive predictive value. Sensitivity and specificity are intrinsic to the test and do not change with prevalence.

Question 6Epidemiology

The crude mortality rate in a region is higher than in another region, but after age adjustment the rates are equal. What does this indicate?

  1. Age adjustment introduces bias
  2. Differences in age distribution explain the crude difference Correct answer.
  3. The regions have identical disease burden
  4. The crude rates were miscalculated

Explanation

Crude rates are influenced by the age structure of a population. Equal age-adjusted rates indicate the difference in crude rates is due to differing age distributions.

Question 7Epidemiology

In an outbreak investigation, what is the primary purpose of a spot map?

  1. Determine the mode of transmission
  2. Display the geographic distribution of cases Correct answer.
  3. Calculate the case fatality rate
  4. Estimate the incubation period

Explanation

A spot map plots the location of cases to reveal spatial clustering. It can suggest a common source or environmental exposure but does not by itself establish transmission mode.

Question 8Epidemiology

Which of the following is the best definition of herd immunity?

  1. Indirect protection of susceptible people when a sufficient proportion of the population is immune Correct answer.
  2. The immunity acquired by an individual after natural infection
  3. The total number of vaccinated persons in a community
  4. The resistance of a pathogen to a vaccine

Explanation

Herd immunity is the indirect protection of unvaccinated or susceptible individuals that arises when enough people are immune to interrupt transmission. It depends on the proportion immune, not on individual immunity alone.

Question 9Epidemiology

A cohort study reports a risk ratio of 2.0 (95% CI 1.2 to 3.3). What is the correct interpretation?

  1. The exposure is associated with a statistically significant increased risk Correct answer.
  2. The study has insufficient power to conclude
  3. The exposure is protective
  4. The association is not statistically significant

Explanation

A confidence interval that excludes 1.0 indicates a statistically significant association. Since the point estimate exceeds 1.0, the exposure is associated with increased risk.

Question 10Epidemiology

Which bias is most likely when cases are identified from hospital records while controls are drawn from the general community?

  1. Selection bias Correct answer.
  2. Information bias
  3. Confounding
  4. Recall bias

Explanation

Selecting cases and controls from different source populations can produce selection bias because exposure-disease relationships differ between the groups. Comparability of the groups is compromised.

Question 11Epidemiology

A factor is a confounder in an exposure-outcome study when it meets which set of criteria?

  1. A consequence of the exposure
  2. Strongly associated with the outcome only
  3. Associated with the exposure and independently a cause of the outcome, but not on the causal pathway Correct answer.
  4. Randomly distributed between groups

Explanation

A confounder must be associated with exposure, be an independent risk factor for the outcome, and not lie on the causal pathway. This creates a spurious or distorted association if uncontrolled.

Question 12Epidemiology

Which measure quantifies the excess risk of disease in the exposed group that can be attributed to the exposure?

  1. Prevalence ratio
  2. Attributable risk Correct answer.
  3. Odds ratio
  4. Relative risk

Explanation

Attributable risk (risk difference) is the absolute difference in risk between exposed and unexposed groups. It represents the excess risk due to exposure.

Question 13Epidemiology

A randomized controlled trial is stopped early because of a large observed benefit. Which concern is most relevant?

  1. Introduction of recall bias
  2. Loss of randomization
  3. Overestimation of effect due to early stopping Correct answer.
  4. Inability to calculate confidence intervals

Explanation

Trials stopped early on the basis of observed benefit tend to overestimate the treatment effect due to random high interim results. Formal stopping rules and adjustment mitigate this.

Question 14Epidemiology

Which of the following best describes the purpose of randomization in a clinical trial?

  1. To balance known and unknown confounders between groups Correct answer.
  2. To eliminate measurement error
  3. To increase the sample size
  4. To guarantee blinding

Explanation

Random assignment tends to distribute both measured and unmeasured confounders evenly across groups. This supports valid comparison of treatment effects.

Question 15Epidemiology

An investigator finds that the association between coffee and pancreatic cancer disappears after adjusting for cigarette smoking. What is the most likely explanation?

  1. The outcome was measured with error
  2. Coffee was misclassified
  3. Smoking confounded the observed association Correct answer.
  4. The study had selection bias

Explanation

When an association attenuates after adjustment for a third variable, that variable is a likely confounder. Smoking is associated with both coffee drinking and pancreatic cancer.

Question 16Epidemiology

Which of the following is an example of a notifiable disease surveillance system?

  1. An ecologic comparison of national mortality data
  2. Mandatory reporting of confirmed measles cases to public health authorities Correct answer.
  3. A one-time seroprevalence survey
  4. A randomized trial of a new vaccine

Explanation

Notifiable disease surveillance requires clinicians and laboratories to report specified diseases to public health agencies. This enables monitoring and response.

Question 17Epidemiology

The incubation period of a disease is best described as which of the following?

  1. The interval between onset of symptoms and death
  2. The interval between exposure and onset of symptoms Correct answer.
  3. The time from diagnosis to recovery
  4. The period during which a person is infectious

Explanation

The incubation period runs from exposure to the appearance of symptoms. It is used in outbreak investigations to infer the time of exposure.

Question 18Epidemiology

Which of the following statements about a pandemic versus an epidemic is correct?

  1. A pandemic is an epidemic that spreads across multiple countries or continents Correct answer.
  2. An epidemic is always more severe than a pandemic
  3. An epidemic refers only to non-infectious diseases
  4. A pandemic is limited to a single community

Explanation

A pandemic is an epidemic of global or multi-continental scale. An epidemic refers to an excess of cases in a defined area or population.

Question 19Epidemiology

In a cohort of 1,000 people followed for one year, 50 develop disease. Assuming all were at risk at the start and follow-up was complete, what is the cumulative incidence?

  1. 50%
  2. 5% Correct answer.
  3. 0.05%
  4. 0.5%

Explanation

Cumulative incidence is the number of new cases divided by the number at risk at the start of follow-up. Here 50/1,000 equals 5%.

Question 20Epidemiology

Which of the following is the most appropriate measure of association for a cross-sectional study?

  1. Case fatality ratio
  2. Incidence rate ratio
  3. Prevalence ratio Correct answer.
  4. Standardized mortality ratio

Explanation

Cross-sectional studies measure exposure and disease simultaneously, so prevalence is the frequency measure used. The prevalence ratio compares prevalences between exposure groups.

Question 21Epidemiology

A screening program detects cases earlier and patients appear to live longer after diagnosis, but the time of death is unchanged. This phenomenon is called which of the following?

  1. Recall bias
  2. Selection bias
  3. Lead-time bias Correct answer.
  4. Length bias

Explanation

Lead-time bias occurs when earlier detection advances the date of diagnosis without changing the time of death, creating apparent survival benefit. Apparent survival gain is an artifact of earlier diagnosis.

Question 22Epidemiology

Which of the following best describes the difference between association and causation in epidemiology?

  1. Association always implies causation
  2. Association is a statistical relationship, while causation requires evidence of a causal mechanism and temporality Correct answer.
  3. Association requires randomization
  4. Causation can be proven by any single observational study

Explanation

An observed association may be due to confounding, bias, or chance, whereas causation requires stronger evidence including temporality and biologic plausibility. Causal inference relies on criteria such as those proposed by Bradford Hill.

Question 23Epidemiology

In a study of a rare disease, which design is generally most efficient for identifying enough cases?

  1. Cross-sectional survey
  2. Randomized controlled trial
  3. Prospective cohort study
  4. Case-control study Correct answer.

Explanation

Case-control studies begin with cases, making them efficient for rare outcomes because they do not require following large populations. Cohorts would need very large samples to accrue enough cases.

Question 24Epidemiology

Which of the following is the correct formula for positive predictive value?

  1. True positives divided by all test positives Correct answer.
  2. True positives divided by all diseased persons
  3. True negatives divided by all non-diseased persons
  4. True negatives divided by all test negatives

Explanation

Positive predictive value is the proportion of people with a positive test who truly have disease. Its denominator is all test-positive individuals.

Question 25Epidemiology

Which of the following best describes an ecologic fallacy?

  1. Failing to adjust for age in a mortality analysis
  2. Misclassifying exposure status in a case-control study
  3. Inferring individual-level associations from group-level data Correct answer.
  4. Applying a cohort result to a different population

Explanation

The ecologic fallacy arises when associations observed at the group level are assumed to hold for individuals. Group averages may not reflect individual relationships.

Question 26Epidemiology

Which measure of disease frequency expresses the number of new cases occurring during a specified period divided by the population at risk at the start of that period?

  1. Point prevalence
  2. Period prevalence
  3. Cumulative incidence Correct answer.
  4. Case fatality ratio

Explanation

Cumulative incidence (risk) counts new cases over a defined period in a denominator of persons at risk at the beginning of the period. It yields a probability of developing disease during that interval.

Question 27Epidemiology

A public health team wants to describe how many people currently have asthma in a city on a single survey day. Which measure should they report?

  1. Incidence rate
  2. Point prevalence Correct answer.
  3. Attack rate
  4. Mortality rate

Explanation

Point prevalence is the proportion of a population with a condition at one specified point in time. A single-day survey captures existing cases rather than new onsets.

Question 28Epidemiology

In a case-control study of a rare cancer, which measure of association is estimated directly from the data?

  1. Incidence rate ratio
  2. Attributable risk percent
  3. Risk ratio
  4. Odds ratio Correct answer.

Explanation

Case-control sampling fixes the number of cases and controls, so disease risk cannot be estimated directly; the odds ratio is the measure obtained. When the disease is rare, the odds ratio approximates the risk ratio.

Question 29Epidemiology

A test has sensitivity of 90% and specificity of 95%. When the same test is applied in a population with a much lower prevalence of the disease, what happens?

  1. Sensitivity falls substantially
  2. Positive predictive value falls Correct answer.
  3. Negative predictive value falls
  4. Specificity rises substantially

Explanation

Predictive values depend on prevalence, while sensitivity and specificity are intrinsic test properties. As prevalence falls, a positive result is more likely to be a false positive, lowering positive predictive value.

Question 30Epidemiology

Which study design follows a defined group forward in time and measures exposure before disease occurs?

  1. Case-control study
  2. Ecologic study
  3. Prospective cohort study Correct answer.
  4. Cross-sectional study

Explanation

A prospective cohort assembles participants, measures exposures, and follows them forward to observe incident outcomes. This temporal ordering supports inference about exposure preceding disease.

Question 31Epidemiology

Investigators want to estimate the incidence of a disease and compute absolute risks in exposed and unexposed groups. Which design is most suitable?

  1. Case-control study
  2. Cohort study Correct answer.
  3. Case series
  4. Ecologic correlation study

Explanation

Only a cohort design provides denominators of persons at risk in each exposure group, allowing direct estimation of incidence and absolute risk. Case-control data yield only the odds ratio.

Question 32Epidemiology

Which of the following is a key advantage of random assignment in a clinical trial?

  1. It guarantees external validity of the results
  2. It eliminates the need for informed consent
  3. It removes measurement error in outcome assessment
  4. It balances known and unknown confounders across groups Correct answer.

Explanation

Randomization tends to distribute both measured and unmeasured confounders evenly between groups, so differences in outcome can be attributed to the intervention. It does not address measurement error or external validity.

Question 33Epidemiology

In a clinical trial, participants and assessors do not know which treatment was given. Which feature does this describe?

  1. Allocation concealment
  2. Blinding Correct answer.
  3. Matching
  4. Stratification

Explanation

Blinding (masking) prevents participants, clinicians, or assessors from knowing the assigned treatment, reducing information and performance bias. Allocation concealment instead hides the upcoming assignment at the moment of randomization.

Question 34Epidemiology

A study reports a relative risk of 3.0 for lung disease among exposed workers. Which statement correctly interprets this value?

  1. Thirty percent of exposed workers will develop the disease
  2. The disease is three times more common in the whole population than expected
  3. Exposed workers have three times the risk of disease compared with unexposed workers Correct answer.
  4. The exposure accounts for three cases per 100 workers

Explanation

A relative risk is a ratio of risks in exposed versus unexposed groups; a value of 3.0 means the exposed group's risk is threefold that of the unexposed group. It conveys no information about absolute risk alone.

Question 35Epidemiology

Which measure estimates the proportion of disease in the population that could be prevented if an exposure were eliminated?

  1. Odds ratio
  2. Population attributable fraction Correct answer.
  3. Standardized mortality ratio
  4. Relative risk

Explanation

The population attributable fraction combines the strength of association with exposure prevalence to estimate the share of disease in the population due to the exposure. It reflects potential impact of removing the exposure.

Question 36Epidemiology

A factor is considered a confounder of an exposure-outcome relationship when it is associated with the outcome and with the exposure but is not which of the following?

  1. Common in the population
  2. Measured accurately
  3. Associated with the outcome
  4. An intermediate step on the causal pathway Correct answer.

Explanation

A confounder must be a common cause of exposure and outcome, not a consequence of the exposure. A variable lying on the causal pathway is a mediator, and adjusting for it would remove part of the true effect.

Question 37Epidemiology

A study finds an association between physical activity and heart disease that weakens but remains after adjusting for age, smoking, and body mass index. What is the best interpretation?

  1. The association is definitely causal
  2. The study must contain selection bias
  3. The association is entirely due to confounding
  4. Residual confounding or other mechanisms may still operate, but an independent association persists Correct answer.

Explanation

Adjustment removes the influence of measured confounders, but unmeasured or imperfectly measured confounders may remain. A persistent association after adjustment is compatible with a real effect but does not by itself establish causation.

Question 38Epidemiology

Which type of bias arises when participants who volunteer for a study differ systematically from those who do not, in ways related to both exposure and outcome?

  1. Regression to the mean
  2. Observer bias
  3. Recall bias
  4. Selection bias Correct answer.

Explanation

Selection bias occurs when the process of choosing participants creates a spurious association between exposure and outcome. Volunteer or referral patterns can produce such distortion.

Question 39Epidemiology

In a case-control study of diet and disease, cases report past food intake more thoroughly than controls because they have been thinking about their illness. Which bias is most likely?

  1. Recall bias Correct answer.
  2. Loss to follow-up
  3. Confounding by indication
  4. Misclassification of the outcome

Explanation

Recall bias is a form of differential information bias in which cases and controls remember or report exposures differently. It distorts the estimate of association because exposure measurement error is related to disease status.

Question 40Epidemiology

Which of the following best describes the purpose of a disease surveillance system?

  1. To determine the efficacy of a new vaccine in a trial
  2. To monitor disease occurrence and trends to guide public health action Correct answer.
  3. To estimate the attributable risk of a specific exposure
  4. To establish causality between risk factors and disease

Explanation

Surveillance collects, analyzes, and disseminates health data continuously so that programs can detect changes and respond. It supports monitoring and control rather than formal causal inference.

Question 41Epidemiology

A screening test is applied to a population, and survival after diagnosis improves while age at death is unchanged. Which phenomenon explains this apparent benefit?

  1. Measurement bias
  2. Length bias
  3. Selection bias
  4. Lead-time bias Correct answer.

Explanation

Lead-time bias occurs when earlier detection advances the date of diagnosis without postponing death, inflating measured survival. Mortality, not survival time from diagnosis, is the appropriate endpoint.

Question 42Epidemiology

Which of the following is the best definition of specificity of a diagnostic test?

  1. The proportion of people with disease who test positive
  2. The proportion of negative tests that are truly disease-free
  3. The proportion of positive tests that are truly diseased
  4. The proportion of people without disease who test negative Correct answer.

Explanation

Specificity is the probability of a negative test among those who do not have the disease, reflecting the test's ability to exclude disease. It is a fixed property of the test at a given cutoff.

Question 43Epidemiology

A disease has an incubation period of 10 to 14 days. In an outbreak investigation, this information is most useful for which purpose?

  1. Estimating the case fatality ratio
  2. Selecting the appropriate antibiotic
  3. Calculating the prevalence of the disease
  4. Determining the period during which exposed persons should be monitored Correct answer.

Explanation

The incubation period defines the interval after exposure during which new cases may appear, guiding the duration of surveillance and quarantine. It also helps identify the likely time of exposure.

Question 44Epidemiology

In an outbreak of gastroenteritis after a banquet, investigators compare food-specific attack rates among those who ate and did not eat each item. What are they primarily trying to identify?

  1. The vehicle of exposure Correct answer.
  2. The case fatality ratio
  3. The incubation period of the agent
  4. The herd immunity threshold

Explanation

Comparing attack rates by exposure item identifies which food was associated with illness, pointing to the vehicle of infection. A markedly higher attack rate among those who ate a specific item implicates it.

Question 45Epidemiology

Which of the following is the best description of the secondary attack rate?

  1. The number of primary cases in a household
  2. The number of new cases per 100,000 population per year
  3. The proportion of cases who die from the disease
  4. The proportion of susceptible contacts who become ill within the accepted incubation period after exposure to a primary case Correct answer.

Explanation

The secondary attack rate measures transmission among susceptible contacts of a known case within the relevant incubation window. It is used to assess infectivity within households or closed settings.

Question 46Epidemiology

A test is applied to 1,000 people: 100 have disease and 90 of them test positive; of the 900 without disease, 90 test positive. What is the positive predictive value?

  1. 0.10
  2. 0.91
  3. 0.90
  4. 0.50 Correct answer.

Explanation

Positive predictive value is true positives divided by all positives: 90/(90+90) = 0.50. The low prevalence of disease among those tested drives the modest predictive value despite high sensitivity.

Question 47Epidemiology

Which of the following statements about a randomized trial that is stopped early for benefit is most accurate?

  1. The results cannot be generalized to any population
  2. Early stopping always eliminates bias from the trial
  3. The observed treatment effect may be exaggerated because of repeated interim analyses Correct answer.
  4. The control group is no longer comparable to the intervention group

Explanation

Repeated looks at accumulating data increase the chance of stopping at a random high point, so effect estimates at early stopping tend to be inflated. Randomization preserves comparability, but the estimate may be biased upward.

Question 48Epidemiology

Which of the following best distinguishes association from causation in epidemiologic research?

  1. Association is a statistical relationship, while causation implies that altering the exposure changes the outcome Correct answer.
  2. Causation can only be demonstrated by cross-sectional studies
  3. Association requires a randomized trial, while causation does not
  4. Association always implies causation when the p value is below 0.05

Explanation

Association is an observed statistical dependence between variables, whereas causation means that a change in the exposure produces a change in the outcome. Confounding, bias, and chance can generate association without causation.

Question 49Epidemiology

Investigators want to judge whether an observed association is likely causal using a framework of criteria. Which of the following is among the widely used considerations?

  1. Sensitivity, specificity, and predictive value
  2. Temporality, strength, consistency, and biological plausibility Correct answer.
  3. Sample size, funding source, and journal impact factor
  4. Prevalence, incidence, and case fatality

Explanation

Causal criteria such as temporality, strength, consistency, dose-response, and plausibility help weigh evidence for causation. Temporality, with exposure preceding outcome, is generally regarded as essential.

Question 50Epidemiology

In a cohort study, 200 exposed persons and 200 unexposed persons are followed. Forty exposed and 10 unexposed develop disease. What is the relative risk?

  1. 2.0
  2. 4.0 Correct answer.
  3. 0.20
  4. 0.25

Explanation

Risk in exposed is 40/200 = 0.20 and in unexposed is 10/200 = 0.05; the ratio is 0.20/0.05 = 4.0. This indicates a fourfold higher risk among the exposed.