Biostatistics: paired t-test: 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: paired t-test

Sample item

Body weight is measured in 30 obese adults before and again after a 12-week lifestyle programme, and the investigator wants to test whether the mean weight has changed. Which test is most appropriate, assuming the differences are normally distributed?

AMann-Whitney U testBChi-square testCPaired t-testDUnpaired t-test

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

The answer and the reasoning

C. Paired t-test

Before and after measurements on the same persons are dependent observations. The paired t-test analyses the mean of the within-person differences against zero. Treating them as two independent groups discards the pairing and loses power.

Option by option

A. Mann-Whitney U test
Mann-Whitney is a non-parametric test for independent groups and is not needed when differences are normal.
B. Chi-square test
Chi-square is for comparing proportions in categorical data, not mean weights.
C. Paired t-test (correct)
Correct. The same subjects are measured twice, so the paired t-test applies.
D. Unpaired t-test
The unpaired test is for two separate groups of different individuals.

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.

Questions about this PSM question

What is the answer to this PSM question?

The best answer is C, Paired t-test. Before and after measurements on the same persons are dependent observations.

Why is "Mann-Whitney U test" not the answer?

Mann-Whitney is a non-parametric test for independent groups and is not needed when differences are normal.

Why is "Chi-square test" not the answer?

Chi-square is for comparing proportions in categorical data, not mean weights.

Why is "Unpaired t-test" not the answer?

The unpaired test is for two separate groups of different individuals.

What concept does this question test?

It tests Biostatistics: paired t-test in PSM. The paired t-test analyses the mean of the within-person differences against zero. Treating them as two independent groups discards the pairing and loses power.

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 Biostatistics: paired t-test?

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.