Epidemiology: kappa statistic: 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: kappa statistic

Sample item

Two radiologists independently classify 200 chest radiographs as normal or abnormal. They agree on 85% of films, and the agreement expected purely by chance is 50%. What is the kappa statistic?

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

The answer and the reasoning

A. 0.70

Kappa measures inter-observer agreement beyond chance: kappa = (observed agreement - chance agreement) / (1 - chance agreement). Here (0.85 - 0.50) / (1 - 0.50) = 0.35 / 0.50 = 0.70. By convention values around 0.61 to 0.80 indicate substantial agreement.

Option by option

  • A. 0.70 (correct)

    Dividing the excess agreement 0.35 by the maximum possible excess 0.50 gives 0.70.

  • B. 0.35

    0.35 is the agreement above chance before dividing by the maximum achievable agreement above chance.

  • C. 0.85

    0.85 is the raw observed agreement, which does not correct for chance.

  • D. 0.50

    0.50 is the agreement expected by chance alone.

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 A, 0.70. Kappa measures inter-observer agreement beyond chance: kappa = (observed agreement - chance agreement) / (1 - chance agreement).

Why is "0.35" not the answer?

0.35 is the agreement above chance before dividing by the maximum achievable agreement above chance.

Why is "0.85" not the answer?

0.85 is the raw observed agreement, which does not correct for chance.

Why is "0.50" not the answer?

0.50 is the agreement expected by chance alone.

What concept does this question test?

It tests Epidemiology: kappa statistic in PSM. Here (0.85 - 0.50) / (1 - 0.50) = 0.35 / 0.50 = 0.70. By convention values around 0.61 to 0.80 indicate substantial agreement.

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 Epidemiology: kappa statistic?

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.