These questions cover epidemiological study designs, measures of disease frequency, and measures of association. They are designed for FRCR Part 1 and SCE Medical Oncology examination preparation.
Which of the following statements about epidemiology are TRUE?
Correct answers: A, B, D are TRUE
Explanation:
A) TRUE – This is the definition of epidemiology: the study of the distribution and determinants of disease in populations.
B) TRUE – A key purpose of epidemiological studies is to identify factors associated with disease occurrence.
C) FALSE – Epidemiological studies are mostly observational in design, in contrast to experimental studies which involve interventions.
D) TRUE – Epidemiology considers a wide range of determinants including biological (age, sex), social (deprivation), behavioural (smoking, diet), and environmental factors.
E) FALSE – Epidemiology was first developed to discover and understand possible causes of infectious diseases like smallpox, typhoid, and polio. It later expanded to include chronic diseases.
Which of the following statements about observational study designs are TRUE?
Correct answers: A, B, C, E are TRUE
Explanation:
A) TRUE – Cross-sectional studies capture a “snapshot” of the population at a single point in time.
B) TRUE – Cohort studies take a group of individuals and follow them forward in time to assess disease occurrence.
C) TRUE – Case-control studies compare the characteristics of cases (with disease) to controls (without disease).
D) FALSE – Observational studies can be either prospective (health event has yet to happen) or retrospective (health event has already occurred). Cohort studies can be either; case-control studies are usually retrospective.
E) TRUE – Ecological studies use aggregated data from groups (e.g., populations defined by geography) rather than individual-level data.
Which of the following statements about the timing of studies are TRUE?
Correct answers: A, B, D, E are TRUE
Explanation:
A) TRUE – Prospective studies follow participants forward from the time of enrolment to observe future outcomes.
B) TRUE – Retrospective studies look backward from the outcome (disease) to investigate prior exposures.
C) FALSE – Cohort studies can be either prospective or retrospective. In a retrospective cohort study, historical records are used to identify the cohort and follow them through to outcomes that have already occurred.
D) TRUE – Case-control studies are usually retrospective because they start with cases who already have the disease and look back at exposures.
E) TRUE – Retrospective cohort studies use existing data (e.g., medical records, employment records) where both exposure and outcome information is already available.
Which of the following statements about prevalence are TRUE?
Correct answers: A, B, C, E are TRUE
Explanation:
A) TRUE – Prevalence is defined as the proportion (or percentage) of individuals with a particular condition in the population.
B) TRUE – Point prevalence = Number with disease at a single time point / Total number studied at that time point.
C) TRUE – Period prevalence = Number with disease over a time period / Total number studied during the same period.
D) FALSE – Prevalence includes all existing cases (both new and pre-existing). Incidence is the measure of new cases.
E) TRUE – Cross-sectional studies are specifically designed to estimate prevalence because they capture a snapshot of disease status at one point in time.
Which of the following statements about incidence are TRUE?
Correct answers: A, B, C, E are TRUE
Explanation:
A) TRUE – Incidence counts only new cases occurring during a specified time period.
B) TRUE – Incidence risk (cumulative incidence) assumes the entire population at risk is followed for the specified period. In practice, this is often not the case.
C) TRUE – Incidence rate uses person-time (typically person-years) in the denominator to account for individuals being lost to follow-up or entering the study at different times.
D) FALSE – Cross-sectional studies cannot measure incidence because they only capture disease status at a single point in time, not new cases over time.
E) TRUE – Cohort studies follow individuals over time and are specifically designed to measure incidence rates.
A cohort study follows 500 women for 5 years. During follow-up, 25 women develop breast cancer. The total person-years of follow-up is 2,300 (some women were lost to follow-up or developed cancer before 5 years).
Which of the following are TRUE?
Correct answers: A, B, C, D, E are all TRUE
Explanation:
A) TRUE – Incidence risk = Number of new cases / Number at risk at start = 25/500 = 0.05 = 5%.
B) TRUE – Incidence rate = Number of new cases / Total person-time = 25/2300 = 0.0109 = 1.09 per 100 person-years.
C) TRUE – When there is loss to follow-up, incidence rate is preferred because it accounts for the actual time each person contributed to the study.
D) TRUE – Person-years sums the follow-up time contributed by each individual, whether they completed the full study or not.
E) TRUE – If all 500 women were followed for the full 5 years: 500 × 5 = 2,500 person-years.
In the standard 2×2 table for a cohort study, which of the following are TRUE?
Correct answers: A, B, C, D are TRUE
Explanation:
Using the standard table layout:
| Disease: Yes | Disease: No | Incidence | |
|---|---|---|---|
| Exposed: Yes | a | b | a/(a+b) |
| Exposed: No | c | d | c/(c+d) |
A) TRUE – Rows represent the exposure categories.
B) TRUE – Columns represent the disease outcome categories.
C) TRUE – Incidence in exposed = a/(a+b), where a = exposed with disease, b = exposed without disease.
D) TRUE – Incidence in unexposed = c/(c+d), where c = unexposed with disease, d = unexposed without disease.
E) FALSE – The relative risk = [a/(a+b)] / [c/(c+d)], not (a+c)/(b+d). The formula compares the incidence in exposed to incidence in unexposed.
A cohort study of smoking and lung cancer reports a relative risk (RR) of 10.0. Which of the following interpretations are TRUE?
Correct answers: A, C, D are TRUE
Explanation:
A) TRUE – RR = 10.0 means the incidence in smokers is 10 times that in non-smokers.
B) FALSE – The risk is 900% higher (RR - 1 = 10 - 1 = 9 = 900%), not 1000%. Smokers have 10 times the risk, which is 9 times more (900% increase).
C) TRUE – RR = 10 represents a strong positive association, as values much greater than 1 indicate substantially elevated risk.
D) TRUE – RR = 1.0 indicates that the risk is identical in exposed and unexposed groups (no association).
E) FALSE – The RR is a ratio of risks. To know the absolute risk, you need the actual incidence rates in each group. For example, RR = 10 could represent 1% vs 0.1%, or 10% vs 1%.
A cohort study investigates low serum ferritin and anaemia in 30 women. The results are:
| Serum Ferritin | Anaemia: Yes | Anaemia: No | Total |
|---|---|---|---|
| Low (<20 μg/L) | 7 | 8 | 15 |
| Normal | 2 | 13 | 15 |
Which of the following are TRUE?
Correct answers: A, B, C, D are TRUE
Explanation:
A) TRUE – Incidence in exposed (low ferritin) = 7/15 = 0.467 = 46.7%.
B) TRUE – Incidence in unexposed (normal ferritin) = 2/15 = 0.133 = 13.3%.
C) TRUE – RR = (7/15)/(2/15) = 0.467/0.133 = 3.5.
D) TRUE – The risk of developing anaemia among women with low serum ferritin is 3.5 times the risk among women with normal ferritin. Alternatively, the risk is 250% higher (3.5 - 1 = 2.5 = 250%).
E) FALSE – RR > 1 indicates an increased risk, not a protective effect. Low ferritin is associated with higher risk of anaemia.
Which of the following statements about case-control studies are TRUE?
Correct answers: A, B, C, E are TRUE
Explanation:
A) TRUE – Cases are defined as individuals who have the disease or condition being studied.
B) TRUE – Controls are individuals without the disease, selected to represent the source population from which cases arose.
C) TRUE – Case-control studies are typically retrospective, looking back from disease status to prior exposures.
D) FALSE – In a case-control study, you cannot calculate incidence because you select patients based on disease status (cases and controls are often selected in equal numbers). The proportion with disease in your study does not reflect the true population incidence.
E) TRUE – We calculate the odds of exposure among cases and compare it to the odds of exposure among controls to obtain the odds ratio.
Which of the following statements about the odds ratio (OR) are TRUE?
Correct answers: A, B, C, D, E are all TRUE
Explanation:
A) TRUE – OR > 1 means the odds of disease is higher in those exposed to the risk factor.
B) TRUE – OR = 1 means the odds of disease is the same in exposed and unexposed groups.
C) TRUE – OR < 1 means exposure is associated with lower odds of disease (protective factor).
D) TRUE – When disease prevalence is low (<10%), the odds ratio closely approximates the relative risk. This is called the “rare disease assumption.”
E) TRUE – The odds ratio is a ratio of two positive quantities (odds), so it must always be positive (ranging from 0 to infinity).
A case-control study investigates oral contraceptive use and breast cancer:
| Oral Contraceptives | Cases (Breast Cancer) | Controls |
|---|---|---|
| Ever used | 537 | 554 |
| Never used | 639 | 622 |
Which of the following are TRUE?
Correct answers: A, B, C, D are TRUE
Explanation:
A) TRUE – Odds in cases = exposed cases / unexposed cases = 537/639 = 0.84.
B) TRUE – Odds in controls = exposed controls / unexposed controls = 554/622 = 0.89.
C) TRUE – OR = (a×d)/(b×c) = (537×622)/(554×639) = 333,914/354,006 = 0.94.
D) TRUE – OR = 0.94 means the odds of breast cancer among contraceptive users is 6% lower than among non-users (1 - 0.94 = 0.06 = 6%).
E) FALSE – OR < 1 actually suggests a slight protective effect (or no meaningful association, given how close to 1.0 it is). It does not suggest increased risk.
Which of the following are advantages of cohort studies?
Correct answers: A, B, C are TRUE
Explanation:
A) TRUE – Because cohort studies follow participants over time, incidence rates can be directly calculated.
B) TRUE – A single cohort can be used to study multiple disease outcomes related to the same exposure.
C) TRUE – By following participants from exposure to outcome, the temporal relationship can be clearly established.
D) FALSE – Cohort studies are typically expensive and require long periods of follow-up, making them resource-intensive.
E) FALSE – Cohort studies are not efficient for rare diseases because you would need to follow a very large cohort to observe enough events. Case-control studies are better for rare diseases.
Which of the following are disadvantages of cohort studies?
Correct answers: A, B, C, D, E are all TRUE
Explanation:
A) TRUE – Loss to follow-up is a major limitation. If participants who drop out differ systematically from those who remain, the results may be biased.
B) TRUE – Diseases that take many years to develop (e.g., many cancers) require very long follow-up periods.
C) TRUE – The resources required to maintain a cohort over many years are substantial.
D) TRUE – If researchers know who is exposed, this may unconsciously influence how they classify outcomes (detection bias).
E) TRUE – Participants may change their exposure (e.g., quit smoking, start exercise), complicating the analysis of exposure-outcome relationships.
Which of the following are advantages of case-control studies?
Correct answers: A, B, C, D are TRUE
Explanation:
A) TRUE – Case-control studies start with people who already have the disease, making them ideal for rare conditions.
B) TRUE – Because they are retrospective and don’t require following participants over time, they are faster and cheaper than cohort studies.
C) TRUE – A wide range of potential risk factors can be assessed in each study by asking about multiple exposures.
D) TRUE – Since data are collected at one point in time (retrospectively), participants cannot be lost to follow-up.
E) FALSE – Case-control studies cannot estimate incidence because participants are selected based on disease status, not randomly from the population.
Which of the following are disadvantages of case-control studies?
Correct answers: A, B, C, D, E are all TRUE
Explanation:
A) TRUE – Selecting controls who represent the source population from which cases arose is challenging and critical to valid results.
B) TRUE – Cases may remember or report exposures differently than controls (recall bias), particularly if they are seeking explanations for their disease.
C) TRUE – Because exposure and disease have both already occurred, it may be difficult to establish whether exposure preceded disease.
D) TRUE – If the exposure is rare, you may need to interview many cases and controls to find enough exposed individuals.
E) TRUE – Only the odds ratio can be calculated; the relative risk cannot be directly estimated because you cannot calculate incidence from a case-control study.
Which of the following statements about confounding are TRUE?
Correct answers: A, C, D, E are TRUE
Explanation:
A) TRUE – To be a confounder, a variable must be associated with both the exposure and the outcome independently.
B) FALSE – A confounder is not on the causal pathway. If it were, controlling for it would be inappropriate (it would be a mediator, not a confounder).
C) TRUE – Confounding can make it appear that there is an association when there isn’t one, or hide a true association.
D) TRUE – Age is frequently associated with both exposures (e.g., older people have had more time to be exposed) and outcomes (e.g., many diseases are more common with age).
E) TRUE – Randomisation balances both known and unknown confounders between groups, which is why RCTs are considered the gold standard for assessing causation.
A comparison of COVID-19 mortality rates between vaccinated and unvaccinated groups shows higher mortality in the vaccinated group. However, age-standardised rates show the opposite. Which statements are TRUE?
Correct answers: A, B, C, D, E are all TRUE
Explanation:
A) TRUE – Crude (unadjusted) rates can be misleading when comparing groups with different age structures.
B) TRUE – If vaccination was prioritised for older people, the vaccinated group would have a higher average age.
C) TRUE – Age standardisation uses a standard population to weight age-specific rates, allowing fair comparison.
D) TRUE – Once you account for age (by looking at age-specific rates), the unvaccinated have higher mortality at each age.
E) TRUE – Age is acting as a confounder: it is associated with both vaccination status (exposure) and mortality (outcome).
Which of the following are among the Bradford-Hill criteria for assessing causation?
Correct answers: A, B, C, D are TRUE
Explanation:
The Bradford-Hill criteria (1965) include:
A) TRUE – Strength: larger effect sizes are more likely to reflect causation.
B) TRUE – Consistency: the association should be reproducible in different settings.
C) TRUE – Temporality: the exposure must come before the disease.
D) TRUE – Biological gradient (dose-response): more exposure should lead to more disease.
E) FALSE – Statistical significance is not one of the Bradford-Hill criteria. The criteria focus on the nature and plausibility of the association, not p-values.
Other Bradford-Hill criteria include: specificity, biological plausibility, coherence, experiment (reversibility), and analogy.
A study finds a strong positive correlation between ice cream sales and drowning deaths. Which of the following statements are TRUE?
Correct answers: B, C, D, E are TRUE
Explanation:
A) FALSE – Correlation does not prove causation. This is a fundamental principle in epidemiology.
B) TRUE – Hot weather is a likely confounding variable: it increases both ice cream consumption and swimming, leading to more drownings.
C) TRUE – Epidemiological studies can only show that a risk factor is associated with disease. They cannot definitively prove causation, though the Bradford-Hill criteria can strengthen causal inference.
D) TRUE – Correlation measures the statistical relationship between variables but does not imply one causes the other.
E) TRUE – A spurious correlation is an apparent association that arises due to confounding or chance rather than a true causal relationship.
Match each measure to the appropriate study design. Which pairings are CORRECT?
Correct answers: A, B, C, D are CORRECT
Explanation:
A) CORRECT – Cross-sectional studies measure disease status at one point in time, providing prevalence estimates.
B) CORRECT – Cohort studies follow participants over time, allowing calculation of incidence rates.
C) CORRECT – Cohort studies provide incidence data needed to calculate relative risk (ratio of incidences).
D) CORRECT – Case-control studies calculate odds ratios because incidence cannot be directly measured.
E) INCORRECT – Case-control studies cannot measure incidence because participants are selected based on disease status, not sampled from the population at risk.
Which of the following are sources of routinely collected data used in epidemiology?
Correct answers: A, B, C, D are TRUE
Explanation:
A) TRUE – Death certificates provide data on mortality rates and causes of death.
B) TRUE – Cancer registries record cancer diagnoses and outcomes, enabling surveillance of cancer incidence and survival.
C) TRUE – Hospital discharge records provide information on diagnoses, procedures, and healthcare utilisation.
D) TRUE – Census data provides population denominators and demographic information essential for calculating rates.
E) FALSE – RCT results are specifically collected for research purposes, not routinely collected administrative data.
After completing these questions, ensure you understand:
Epidemiological Concepts:
Measures of Disease Frequency:
Measures of Association:
Study Design Selection:
| Study Design | Direction | Main Measure | Best For |
|---|---|---|---|
| Cross-sectional | Single time point | Prevalence | Describing current health status |
| Cohort | Forward (prospective) | Relative Risk | Assessing incidence and causation |
| Case-control | Backward (retrospective) | Odds Ratio | Investigating rare diseases |
Causation:
These questions are designed for FRCR Part 1 and SCE Medical Oncology examination preparation. Based on course materials from Edinburgh Cancer Informatics.