Biostatistics: intention-to-treat 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 · Biostatistics: intention-to-treat analysis

Sample item

In a randomised trial of a new antihypertensive, 20 of 200 patients allocated to the new drug stopped it within a month because of side effects. The trialist analyses all 200 in the group to which they were randomised. What is this approach called and why is it preferred?

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

The answer and the reasoning

B. Intention-to-treat analysis, which preserves the balance created by randomisation

In intention-to-treat analysis every participant is analysed in the arm to which he or she was randomised, regardless of adherence. This keeps the groups comparable and reflects the effect of a treatment policy in real practice. Excluding non-adherers can reintroduce bias because they often differ systematically.

Option by option

  • A. Per-protocol analysis, which gives the purest estimate of biological efficacy

    Per-protocol analysis would exclude non-adherers and could bias the comparison.

  • B. Intention-to-treat analysis, which preserves the balance created by randomisation (correct)

    Correct. Analysis by original allocation protects randomisation.

  • C. As-treated analysis, which removes bias from drop-outs

    As-treated analysis regroups patients by the drug received and breaks randomisation.

  • D. Subgroup analysis, which tests effect in side-effect sufferers

    Subgroup analysis examines a defined stratum and does not describe analysing all randomised patients.

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, Intention-to-treat analysis, which preserves the balance created by randomisation. In intention-to-treat analysis every participant is analysed in the arm to which he or she was randomised, regardless of adherence.

Why is "Per-protocol analysis, which gives the purest estimate of biological…" not the answer?

Per-protocol analysis would exclude non-adherers and could bias the comparison.

Why is "As-treated analysis, which removes bias from drop-outs" not the answer?

As-treated analysis regroups patients by the drug received and breaks randomisation.

Why is "Subgroup analysis, which tests effect in side-effect sufferers" not the answer?

Subgroup analysis examines a defined stratum and does not describe analysing all randomised patients.

What concept does this question test?

It tests Biostatistics: intention-to-treat analysis in PSM. This keeps the groups comparable and reflects the effect of a treatment policy in real practice. Excluding non-adherers can reintroduce bias because they often differ systematically.

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 Biostatistics: intention-to-treat 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.