Epidemiology: 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 · Epidemiology: intention-to-treat analysis

Sample item

In a randomised trial comparing surgery with medical therapy, 15 of the 100 patients assigned to surgery refuse the operation and receive medical therapy instead. The investigators analyse all 100 patients in the surgery group as originally allocated. Which principle does this represent, and what is its main advantage?

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 baseline comparability created by randomisation

In intention-to-treat analysis, participants are analysed in the groups to which they were randomised, whatever treatment they actually received. This keeps the groups comparable in known and unknown confounders and reflects real-world effectiveness, including non-adherence. Dropping or moving crossovers breaks the balance achieved by randomisation.

Option by option

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

    Per-protocol analysis would include only those who completed the allocated treatment, which reintroduces selection bias.

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

    Correct. Analysis by original allocation maintains the balance produced by randomisation.

  • C. As-treated analysis, which removes the effect of non-compliance

    As-treated analysis regroups patients by the treatment actually received, which destroys randomisation.

  • D. Subgroup analysis, which identifies the patients who benefit most

    Subgroup analysis examines selected strata and is not defined by analysing patients as originally assigned.

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.

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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 baseline comparability created by randomisation. In intention-to-treat analysis, participants are analysed in the groups to which they were randomised, whatever treatment they actually received.

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

Per-protocol analysis would include only those who completed the allocated treatment, which reintroduces selection bias.

Why is "As-treated analysis, which removes the effect of non-compliance" not the answer?

As-treated analysis regroups patients by the treatment actually received, which destroys randomisation.

Why is "Subgroup analysis, which identifies the patients who benefit most" not the answer?

Subgroup analysis examines selected strata and is not defined by analysing patients as originally assigned.

What concept does this question test?

It tests Epidemiology: intention-to-treat analysis in PSM. This keeps the groups comparable in known and unknown confounders and reflects real-world effectiveness, including non-adherence. Dropping or moving crossovers breaks the balance achieved by randomisation.

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: 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.