Biostatistics: probability and odds: 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 · Biostatistics: probability and odds

Sample item

The probability of a patient responding to a drug is 0.2. What are the odds of response?

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

The answer and the reasoning

D. 0.25

Odds are the probability of the event divided by the probability of no event, 0.2 divided by 0.8, which is 0.25. Probability and odds are close only when the event is rare. The odds of 4 would be the odds of not responding.

Option by option

  • A. 0.20

    This repeats the probability, which is not the odds.

  • B. 4

    This is the odds of no response, 0.8 divided by 0.2.

  • C. 0.8

    This is the probability of no response, not the odds of response.

  • D. 0.25 (correct)

    Correct. 0.2 divided by 0.8 gives odds of 0.25.

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, 0.25. Odds are the probability of the event divided by the probability of no event, 0.

Why is "0.20" not the answer?

This repeats the probability, which is not the odds.

Why is "4" not the answer?

This is the odds of no response, 0.8 divided by 0.2.

Why is "0.8" not the answer?

This is the probability of no response, not the odds of response.

What concept does this question test?

It tests Biostatistics: probability and odds in PSM. 2 divided by 0.8, which is 0.25. Probability and odds are close only when the event is rare. The odds of 4 would be the odds of not responding.

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 Biostatistics: probability and odds?

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.