Screening tests: 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 · Screening tests

Sample item

Why can the positive predictive value of a screening test fall when the disease is very rare?

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

The answer and the reasoning

D. False positives may outnumber true positives

When disease prevalence is low, even a highly specific test can generate more false positives than true positives, so a positive result has a lower probability of representing real disease and may require confirmatory testing.

Option by option

  • A. Specificity always becomes zero

    Specificity does not automatically become zero in rare disease.

  • B. Sensitivity becomes mathematically impossible

    Sensitivity remains a property of the test and does not become impossible.

  • C. The test no longer needs confirmation

    Low predictive value makes confirmation more, not less, important.

  • D. False positives may outnumber true positives (correct)

    Correct: low prevalence increases the proportion of positive results that are false.

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.

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Questions about this PSM question

What is the answer to this PSM question?

The best answer is D, False positives may outnumber true positives. When disease prevalence is low, even a highly specific test can generate more false positives than true positives, so a positive result has a lower probability of representing real disease and may require confirmatory testing.

Why is "Specificity always becomes zero" not the answer?

Specificity does not automatically become zero in rare disease.

Why is "Sensitivity becomes mathematically impossible" not the answer?

Sensitivity remains a property of the test and does not become impossible.

Why is "The test no longer needs confirmation" not the answer?

Low predictive value makes confirmation more, not less, important.

What concept does this question test?

It tests Screening tests in PSM. The correct option holds because: Correct: low prevalence increases the proportion of positive results that are false.

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 Screening tests?

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.