Biostatistics: geometric mean: 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.

Try it

PSM · Biostatistics: geometric mean

Sample item

Antibody titres in three vaccinated infants are 2, 8 and 32 (fold dilution values spaced geometrically). Which summary measure is appropriate for such data, and what is its value here?

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

The answer and the reasoning

C. Geometric mean, 8

Titres and other ratio-type data that grow multiplicatively are summarised by the geometric mean, the nth root of the product. Here the cube root of 2 x 8 x 32 = 512 is 8. The arithmetic mean of 14 is pulled upward by the highest titre.

Option by option

  • A. Arithmetic mean, 14

    The arithmetic mean is 14, but it is distorted by the largest value in multiplicatively spaced data.

  • B. Harmonic mean, 4.6

    The harmonic mean (about 4.6) is used for rates and is not standard for titres.

  • C. Geometric mean, 8 (correct)

    Correct. The cube root of 512 is 8.

  • D. Mid-range, 17

    The mid-range of 17 uses only the extreme values and ignores the rest.

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 C, Geometric mean, 8. Titres and other ratio-type data that grow multiplicatively are summarised by the geometric mean, the nth root of the product.

Why is "Arithmetic mean, 14" not the answer?

The arithmetic mean is 14, but it is distorted by the largest value in multiplicatively spaced data.

Why is "Harmonic mean, 4.6" not the answer?

The harmonic mean (about 4.6) is used for rates and is not standard for titres.

Why is "Mid-range, 17" not the answer?

The mid-range of 17 uses only the extreme values and ignores the rest.

What concept does this question test?

It tests Biostatistics: geometric mean in PSM. Here the cube root of 2 x 8 x 32 = 512 is 8. The arithmetic mean of 14 is pulled upward by the highest titre.

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: geometric mean?

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.