skip to main content

Point prevalence — MRCPsych Paper A MCQ

Instant feedback + full explanation. One question, done properly.

HardEpidemiology and research methodsPoint prevalenceMRCPsych Paper A

On 1 July, a cross-sectional survey administers a structured PTSD interview to a representative sample of adults. Although symptoms during the preceding month are used as the recall window, each participant is classified according to whether they meet full PTSD criteria on 1 July. The numerator includes all current cases on that date, irrespective of when PTSD began, and the denominator is everyone assessed on that date. Which epidemiological measure is being estimated?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — Point prevalence

The answer is E, point prevalence: the numerator is everyone who has PTSD on the single index date, divided by the population assessed on that date. It includes both recent and longstanding cases. The preceding-month questions are only the diagnostic recall window and do not make this period prevalence. One-month period prevalence would include anyone who met criteria at any time during that month, even if they were not a case on 1 July. Incidence rate counts new cases arising per person-time among people initially at risk. Lifetime risk estimates the probability of developing PTSD over a lifetime. Attributable risk compares disease risk between exposed and unexposed groups to estimate excess risk associated with an exposure.

Reference: BMJ, Epidemiology for the uninitiated, Chapter 2: Quantifying disease in populations, section on prevalence, accessed 2026. https://www.bmj.com/about-bmj/resources-readers/publications/epidemiology-uninitiated/2-quantifying-disease-populations