Epidemiology: period prevalence: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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PSM · Epidemiology: period prevalence

Sample item

A survey counts all persons who had bronchial asthma at any time during the calendar year, including those whose illness began during that year, and divides by the mid-year population. This measure is:

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Period prevalence

Period prevalence counts all existing cases, old and new, during a stated period divided by the population. Point prevalence is a snapshot at one moment, and incidence counts only new cases. Because it includes both pre-existing and new cases, period prevalence is not an incidence measure.

Option by option

  • A. Cumulative incidence

    Cumulative incidence counts only new cases among those initially free of disease.

  • B. Incidence density

    Incidence density uses new cases over person-time and excludes existing cases.

  • C. Period prevalence (correct)

    Correct. Old and new cases over an interval make up period prevalence.

  • D. Point prevalence

    Point prevalence counts cases at a single instant, not across a year.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

More PSM questions

Questions about this PSM question

What is the answer to this PSM question?

The best answer is C, Period prevalence. Period prevalence counts all existing cases, old and new, during a stated period divided by the population.

Why is "Cumulative incidence" not the answer?

Cumulative incidence counts only new cases among those initially free of disease.

Why is "Incidence density" not the answer?

Incidence density uses new cases over person-time and excludes existing cases.

Why is "Point prevalence" not the answer?

Point prevalence counts cases at a single instant, not across a year.

What concept does this question test?

It tests Epidemiology: period prevalence in PSM. Point prevalence is a snapshot at one moment, and incidence counts only new cases. Because it includes both pre-existing and new cases, period prevalence is not an incidence measure.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Epidemiology: period prevalence?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.