Epidemiology: per-protocol analysis: 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: per-protocol analysis

Sample item

A trial analyses only those participants who took the assigned treatment as planned and had no protocol violations, leaving out dropouts and crossovers. Which analysis is this, and what is its main weakness?

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

The answer and the reasoning

B. Per-protocol analysis, which can undo the balance from randomisation

A per-protocol analysis includes only compliant participants, so the groups may no longer be comparable because those who drop out are often systematically different. Intention-to-treat analysis keeps everyone in the group to which they were randomised and preserves the benefit of randomisation. Per-protocol results answer a question about efficacy under ideal adherence.

Option by option

  • A. Subgroup analysis, which always lacks adequate statistical power

    A subgroup analysis divides participants by a characteristic, not by adherence.

  • B. Per-protocol analysis, which can undo the balance from randomisation (correct)

    Correct. Restricting to compliers breaks the balance created by randomisation.

  • C. Per-protocol analysis, which retains every participant who was randomised

    Per-protocol analysis leaves out non-adherent patients and does not keep all randomised ones.

  • D. Intention-to-treat analysis, which tends to overestimate the true effect

    Intention-to-treat analysis keeps all randomised participants, which is the opposite of what is described.

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 B, Per-protocol analysis, which can undo the balance from randomisation. A per-protocol analysis includes only compliant participants, so the groups may no longer be comparable because those who drop out are often systematically different.

Why is "Subgroup analysis, which always lacks adequate statistical power" not the answer?

A subgroup analysis divides participants by a characteristic, not by adherence.

Why is "Per-protocol analysis, which retains every participant who was random…" not the answer?

Per-protocol analysis leaves out non-adherent patients and does not keep all randomised ones.

Why is "Intention-to-treat analysis, which tends to overestimate the true eff…" not the answer?

Intention-to-treat analysis keeps all randomised participants, which is the opposite of what is described.

What concept does this question test?

It tests Epidemiology: per-protocol analysis in PSM. Intention-to-treat analysis keeps everyone in the group to which they were randomised and preserves the benefit of randomisation. Per-protocol results answer a question about efficacy under ideal adherence.

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: per-protocol analysis?

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.