MCCQE Population Health and Epidemiology 2

Question 1

A study follows 1,000 smokers and 1,000 non-smokers for 10 years to compare lung cancer incidence. What type of study is this?

Accepted Answer

Prospective cohort study

Answer

A prospective cohort study follows groups with different exposures forward in time to measure disease incidence.

Question 2

In a screening program, the positive predictive value of a test is most influenced by which of the following?

Accepted Answer

Prevalence of the disease in the screened population

Answer

Positive predictive value depends heavily on disease prevalence; a highly specific test still has low PPV in low-prevalence populations.

Question 3

Which measure of disease frequency accounts for the time each individual is at risk?

Accepted Answer

Incidence rate (person-time)

Answer

Incidence rate (incidence density) uses person-time denominators to account for variable follow-up periods.

Question 4

A public health intervention reduces the relative risk of stroke from 0.40 to 0.20. What is the relative risk reduction?

Accepted Answer

50%

Answer

Relative risk reduction = (RR_old − RR_new) / RR_old = (0.40 − 0.20) / 0.40 = 50%.

Question 5

Herd immunity thresholds are primarily determined by which parameter?

Accepted Answer

Basic reproduction number (R₀)

Answer

The herd immunity threshold is calculated as 1 − 1/R₀; a higher R₀ requires greater population immunity.

(MCCQE) Medical Council of Canada Qualifying Examination Practice Test