Epidemiology: odds ratio: 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: odds ratio

Sample item

In a case-control study of 100 cases and 100 controls, 40 cases and 20 controls were exposed to a risk factor. What is the odds ratio?

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

The answer and the reasoning

D. 2.7

Odds of exposure in cases = 40/60; odds in controls = 20/80. The odds ratio = (40 × 80) / (60 × 20) = 3200 / 1200 ≈ 2.7. A value above 1 suggests a positive association. Relative risk cannot be calculated directly in a case-control design.

Option by option

  • A. 2.0

    This is the ratio of the exposed proportions (40/20), which is not the odds ratio.

  • B. 0.5

    This is the inverse of 2 and does not match the data.

  • C. 1.5

    This value does not follow from the cross-product ratio of the table.

  • D. 2.7 (correct)

    Correct. (40 × 80) ÷ (60 × 20) ≈ 2.7.

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 D, 2.7. Odds of exposure in cases = 40/60; odds in controls = 20/80.

Why is "2.0" not the answer?

This is the ratio of the exposed proportions (40/20), which is not the odds ratio.

Why is "0.5" not the answer?

This is the inverse of 2 and does not match the data.

Why is "1.5" not the answer?

This value does not follow from the cross-product ratio of the table.

What concept does this question test?

It tests Epidemiology: odds ratio in PSM. The odds ratio = (40 × 80) / (60 × 20) = 3200 / 1200 ≈ 2.7. A value above 1 suggests a positive association. Relative risk cannot be calculated directly in a case-control design.

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: odds ratio?

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.