Epidemiology: 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

Sample item

An outbreak investigation covers 25 households, each with one primary case. Among 100 susceptible household contacts, 15 develop the disease within one incubation period. What is the secondary attack rate?

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

The answer and the reasoning

A. 15 percent

The secondary attack rate is the number of new cases among susceptible contacts in the incubation period divided by the total number of susceptible contacts. Here it is 15 divided by 100, or 15 percent. Primary cases are excluded from the numerator and denominator.

Option by option

  • A. 15 percent (correct)

    Correct. 15 secondary cases among 100 susceptible contacts.

  • B. 12 percent

    12 percent wrongly adds the primary cases to the denominator.

  • C. 60 percent

    60 percent divides the secondary cases by the number of primary cases.

  • D. 25 percent

    25 percent uses the household count as a denominator.

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, 15 percent. The secondary attack rate is the number of new cases among susceptible contacts in the incubation period divided by the total number of susceptible contacts.

Why is "12 percent" not the answer?

12 percent wrongly adds the primary cases to the denominator.

Why is "60 percent" not the answer?

60 percent divides the secondary cases by the number of primary cases.

Why is "25 percent" not the answer?

25 percent uses the household count as a denominator.

What concept does this question test?

It tests Epidemiology in PSM. Here it is 15 divided by 100, or 15 percent. Primary cases are excluded from the numerator and denominator.

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?

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.