Screening: ROC curve: 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: ROC curve

Sample item

Two screening tests are evaluated for the same condition. Test A has an area under the receiver operating characteristic curve of 0.55 and test B has 0.90. What is the correct interpretation?

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

The answer and the reasoning

D. Test B discriminates diseased from healthy people far better, whereas test A is little better than chance

The ROC curve plots sensitivity against 1 minus specificity across cut-offs. An area of 0.5 means no discriminating ability, equal to chance, and 1.0 means perfect discrimination. A larger area, such as 0.90, shows better overall test performance.

Option by option

  • A. Test A is more sensitive than test B at every cut-off

    The area summarises overall performance and does not show higher sensitivity at every cut-off, and 0.55 is poorer.

  • B. Test A is better because its curve lies closer to the diagonal line

    A curve close to the diagonal represents chance performance, which is worse.

  • C. Both tests are equally accurate, because areas above 0.5 are equivalent

    The size of the area matters; a value near 0.5 is useless.

  • D. Test B discriminates diseased from healthy people far better, whereas test A is little better than chance (correct)

    Correct. An area of 0.90 shows strong discrimination and 0.55 is close to chance.

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, Test B discriminates diseased from healthy people far better, whereas test A is little better than chance. The ROC curve plots sensitivity against 1 minus specificity across cut-offs.

Why is "Test A is more sensitive than test B at every cut-off" not the answer?

The area summarises overall performance and does not show higher sensitivity at every cut-off, and 0.55 is poorer.

Why is "Test A is better because its curve lies closer to the diagonal line" not the answer?

A curve close to the diagonal represents chance performance, which is worse.

Why is "Both tests are equally accurate, because areas above 0.5 are equivale…" not the answer?

The size of the area matters; a value near 0.5 is useless.

What concept does this question test?

It tests Screening: ROC curve in PSM. An area of 0.5 means no discriminating ability, equal to chance, and 1.0 means perfect discrimination. A larger area, such as 0.90, shows better overall test performance.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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: ROC curve?

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.