Biostatistics: Wilcoxon signed-rank 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: Wilcoxon signed-rank test

Sample item

Pain scores on an ordinal scale are recorded in 15 patients before and after a physiotherapy session. The differences are clearly skewed. Which test should be used to compare the two sets of scores?

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

The answer and the reasoning

B. Wilcoxon signed-rank test

The Wilcoxon signed-rank test is the non-parametric counterpart of the paired t-test and is used for paired ordinal or non-normal data. Mann-Whitney and Kruskal-Wallis are for independent groups. The paired t-test needs normally distributed differences.

Option by option

  • A. Kruskal-Wallis test

    Kruskal-Wallis compares three or more independent groups.

  • B. Wilcoxon signed-rank test (correct)

    Correct. Paired data that are ordinal or skewed call for the signed-rank test.

  • C. Paired t-test

    The paired t-test assumes normally distributed differences, which is violated here.

  • D. Mann-Whitney U test

    Mann-Whitney U compares two independent groups, not paired measurements.

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, Wilcoxon signed-rank test. The Wilcoxon signed-rank test is the non-parametric counterpart of the paired t-test and is used for paired ordinal or non-normal data.

Why is "Kruskal-Wallis test" not the answer?

Kruskal-Wallis compares three or more independent groups.

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

The paired t-test assumes normally distributed differences, which is violated here.

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

Mann-Whitney U compares two independent groups, not paired measurements.

What concept does this question test?

It tests Biostatistics: Wilcoxon signed-rank test in PSM. Mann-Whitney and Kruskal-Wallis are for independent groups. The paired t-test needs normally distributed differences.

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: Wilcoxon signed-rank 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.