Screening: 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

Sample item

A screening test has sensitivity 90 percent and specificity 70 percent. What is its positive likelihood ratio?

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

The answer and the reasoning

C. 3

The positive likelihood ratio equals sensitivity divided by (1 minus specificity), here 0.90 divided by 0.30, which equals 3. A positive result is thus three times as likely in diseased as in non-diseased persons. The negative ratio, (1 minus sensitivity) divided by specificity, is 0.10 divided by 0.70, about 0.14.

Option by option

  • A. 0.14

    0.14 is the negative likelihood ratio.

  • B. 1.3

    1.3 results from dividing sensitivity by specificity.

  • C. 3 (correct)

    Correct. LR+ is sensitivity over the false positive rate.

  • D. 0.33

    0.33 is the inverse of the positive likelihood ratio.

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, 3. The positive likelihood ratio equals sensitivity divided by (1 minus specificity), here 0.

Why is "0.14" not the answer?

0.14 is the negative likelihood ratio.

Why is "1.3" not the answer?

1.3 results from dividing sensitivity by specificity.

Why is "0.33" not the answer?

0.33 is the inverse of the positive likelihood ratio.

What concept does this question test?

It tests Screening in PSM. 90 divided by 0.30, which equals 3. A positive result is thus three times as likely in diseased as in non-diseased persons. The negative ratio, (1 minus sensitivity) divided by specificity, is 0.10 divided by 0.70, about 0.14.

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?

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.