Epidemiology: case-crossover design: 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: case-crossover design

Sample item

To study whether mobile phone use triggers road crashes, investigators compare each crashed driver's phone use in the minutes before the crash with the same driver's use during an earlier period of normal driving. Which design is this?

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

The answer and the reasoning

D. Case-crossover study

In a case-crossover study each case serves as his or her own control, comparing exposure just before the event with exposure at another time. It suits brief exposures with transient effects and removes confounding by stable traits. A crossover trial, by contrast, is an experiment in which the investigator assigns treatments.

Option by option

  • A. Crossover clinical trial

    A crossover trial involves treatments assigned by investigators, not observed exposures.

  • B. Nested case-control study

    A nested case-control study samples controls from a cohort rather than using the cases themselves.

  • C. Case series

    A case series describes cases without a comparison period or group.

  • D. Case-crossover study (correct)

    Correct. Self-matched comparison of exposure before the event and in a control period defines this design.

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, Case-crossover study. In a case-crossover study each case serves as his or her own control, comparing exposure just before the event with exposure at another time.

Why is "Crossover clinical trial" not the answer?

A crossover trial involves treatments assigned by investigators, not observed exposures.

Why is "Nested case-control study" not the answer?

A nested case-control study samples controls from a cohort rather than using the cases themselves.

Why is "Case series" not the answer?

A case series describes cases without a comparison period or group.

What concept does this question test?

It tests Epidemiology: case-crossover design in PSM. It suits brief exposures with transient effects and removes confounding by stable traits. A crossover trial, by contrast, is an experiment in which the investigator assigns treatments.

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: case-crossover design?

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.