MCCQE - Medical Council of Canada Qualifying Examination Population Health and Epidemiology Questions and Answers 1 — Questions and Answers
Question 1: Researchers wish to investigate a potential link between a rare form of cancer and exposure to a specific industrial solvent. They identify 100 individuals with this cancer and a comparison group of 200 individuals without the cancer, matched for age and sex. They then proceed to collect detailed occupational histories from all participants to determine past exposure to the solvent. Which study design does this best describe?
- Prospective Cohort Study
- Case-Control Study (Correct answer)
- Randomized Controlled Trial
- Cross-Sectional Study
Correct answer: Case-Control Study
This is a case-control study. The design starts by identifying individuals with the disease (cases) and a group without the disease (controls), and then looks back retrospectively to compare the frequency of past exposure to a risk factor. This approach is particularly efficient for studying rare diseases.
Question 2: A cohort study followed a group of 5,000 factory workers for 10 years. Among 2,000 workers exposed to a chemical, 100 developed bladder cancer. Among the 3,000 unexposed workers, 60 developed bladder cancer. What is the relative risk (RR) of developing bladder cancer for the exposed workers compared to the unexposed workers?
- 1.67
- 0.60
- 2.50 (Correct answer)
- 30.0
Correct answer: 2.50
First, calculate the incidence in each group. Incidence in exposed = 100/2000 = 0.05. Incidence in unexposed = 60/3000 = 0.02. The Relative Risk (RR) is the ratio of the incidence in the exposed group to the incidence in the unexposed group. RR = 0.05 / 0.02 = 2.50. This means the exposed workers were 2.5 times as likely to develop bladder cancer as the unexposed workers.
Question 3: A hospital-based study aims to determine if smoking is a risk factor for pancreatitis. Cases are recruited from the hospital's gastroenterology ward. Controls are recruited from the hospital's pulmonary ward, which treats many patients with smoking-related diseases. This study design is most susceptible to which type of bias?
- Recall bias
- Observer bias
- Confounding
- Selection bias (Correct answer)
Correct answer: Selection bias
This is a form of selection bias, specifically Berkson's bias. The control group is not representative of the general population from which the cases arose. Because the control group (pulmonary patients) has a much higher prevalence of smoking than the general population, the association between smoking and pancreatitis may be artificially weakened or missed entirely.
Question 4: A community health centre implements a program offering regular foot care, retinal screening, and self-management education workshops for individuals already diagnosed with type 2 diabetes. This initiative is an example of which level of prevention?
- Primary prevention
- Secondary prevention
- Tertiary prevention (Correct answer)
- Primordial prevention
Correct answer: Tertiary prevention
Tertiary prevention aims to soften the impact of an ongoing illness or injury that has lasting effects. These activities for patients with established diabetes are designed to prevent complications (like foot ulcers, blindness) and improve quality of life, which is the goal of tertiary prevention.
Question 5: Which of the following is a key principle, as originally described by Wilson and Jungner, for a condition to be suitable for a population-based screening program?
- The treatment for the disease must be inexpensive and easily accessible.
- The condition must have a recognizable latent or early symptomatic stage. (Correct answer)
- The screening test must have 100% specificity to avoid false positives.
- The condition must have a high prevalence in the target population.
Correct answer: The condition must have a recognizable latent or early symptomatic stage.
A core Wilson-Jungner criterion is that the natural history of the condition should be understood, including a detectable early stage (latent or early symptomatic) during which treatment is more effective than if applied later. This allows the screening program to identify and treat the disease early, thereby improving the outcome.
Question 6: Following a large company picnic, 45 of the 100 employees who ate potato salad developed gastroenteritis, while 10 of the 200 employees who did not eat the potato salad developed the same symptoms. What is the primary purpose of calculating the attack rates for these two groups?
- To determine the case-fatality rate of the illness.
- To calculate the odds ratio of the exposure.
- To identify the likely source of the foodborne outbreak. (Correct answer)
- To establish the incubation period of the pathogen.
Correct answer: To identify the likely source of the foodborne outbreak.
Calculating and comparing attack rates between exposed and unexposed groups is a fundamental step in an outbreak investigation to identify the source. In this case, the attack rate for those who ate the salad is 45/100 (45%), and for those who did not, it's 10/200 (5%). The significantly higher attack rate in the exposed group strongly implicates the potato salad as the source of the outbreak.
MCCQE - Medical Council of Canada Qualifying Examination Population Health and Epidemiology Questions and Answers 1
Researchers wish to investigate a potential link between a rare form of cancer and exposure to a specific industrial solvent.
They identify 100 individuals with this cancer and a comparison group of 200 individuals without the cancer, matched for age and sex.
They then proceed to collect detailed occupational histories from all participants to determine past exposure to the solvent.
Which study design does this best describe?