Family planning: Pearl index: 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 · Family planning: Pearl index

Sample item

In a study of a contraceptive method, 250 women use it for 12 months each, and 5 accidental pregnancies occur. What is the Pearl index?

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

The answer and the reasoning

A. 2.0 per 100 woman-years

The Pearl index is the number of accidental pregnancies per 100 woman-years of exposure: (failures x 1200) / total months of exposure. Here 250 women x 12 months = 3000 woman-months, so the index is 5 x 1200 / 3000 = 2.0. It measures method failure over the period of use.

Option by option

  • A. 2.0 per 100 woman-years (correct)

    5 x 1200 / 3000 gives 2.0 failures per 100 woman-years.

  • B. 0.5 per 100 woman-years

    0.5 would correspond to roughly one pregnancy in 250 woman-years, not five.

  • C. 20 per 100 woman-years

    20 inflates the result, as 250 woman-years of exposure gives 2 per 100, not 20.

  • D. 5.0 per 100 woman-years

    5.0 counts the number of failures without relating them to exposure.

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, 2.0 per 100 woman-years. The Pearl index is the number of accidental pregnancies per 100 woman-years of exposure: (failures x 1200) / total months of exposure.

Why is "0.5 per 100 woman-years" not the answer?

0.5 would correspond to roughly one pregnancy in 250 woman-years, not five.

Why is "20 per 100 woman-years" not the answer?

20 inflates the result, as 250 woman-years of exposure gives 2 per 100, not 20.

Why is "5.0 per 100 woman-years" not the answer?

5.0 counts the number of failures without relating them to exposure.

What concept does this question test?

It tests Family planning: Pearl index in PSM. Here 250 women x 12 months = 3000 woman-months, so the index is 5 x 1200 / 3000 = 2.0. It measures method failure over the period of use.

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 Family planning: Pearl index?

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.