Epidemiology: crossover trial 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: crossover trial design

Sample item

In a trial, 40 patients receive drug A for 4 weeks, then no drug for 2 weeks, and then drug B for 4 weeks. What is the main purpose of the 2-week gap?

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

The answer and the reasoning

C. Washout, to avoid carry-over of drug A effects

In a crossover design each participant acts as their own control, receiving both treatments in sequence. A washout period lets the effect of the first drug disappear so that it does not contaminate the second period. It suits stable chronic conditions.

Option by option

  • A. Reducing loss to follow up

    A gap does not improve follow up and may worsen dropout.

  • B. Allocation concealment

    Allocation concealment hides the upcoming assignment during randomisation, not between periods.

  • C. Washout, to avoid carry-over of drug A effects (correct)

    Correct. A washout period prevents carry-over effects.

  • D. Maintaining blinding of the investigator

    Blinding is achieved with identical-looking preparations, not with a gap.

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 C, Washout, to avoid carry-over of drug A effects. In a crossover design each participant acts as their own control, receiving both treatments in sequence.

Why is "Reducing loss to follow up" not the answer?

A gap does not improve follow up and may worsen dropout.

Why is "Allocation concealment" not the answer?

Allocation concealment hides the upcoming assignment during randomisation, not between periods.

Why is "Maintaining blinding of the investigator" not the answer?

Blinding is achieved with identical-looking preparations, not with a gap.

What concept does this question test?

It tests Epidemiology: crossover trial design in PSM. A washout period lets the effect of the first drug disappear so that it does not contaminate the second period. It suits stable chronic conditions.

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 Epidemiology: crossover trial 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.