Biostatistics: standard score: 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: standard score

Sample item

A child weighs 14 kg. In the reference population of the same age and sex the mean weight is 12 kg and the standard deviation is 1 kg. What is the Z score?

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

The answer and the reasoning

A. +2

Z equals the observed value minus the mean divided by the standard deviation: (14 minus 12) divided by 1 gives +2. It states how many standard deviations the value lies from the mean, which is how growth standards are expressed.

Option by option

  • A. +2 (correct)

    Correct. (14 minus 12) divided by 1 is +2.

  • B. +0.5

    0.5 comes from inverting the ratio, dividing the SD by the difference.

  • C. +12

    12 is the reference mean, not the Z score.

  • D. +14

    14 is the raw weight and was not standardised.

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 A, +2. Z equals the observed value minus the mean divided by the standard deviation: (14 minus 12) divided by 1 gives +2.

Why is "+0.5" not the answer?

0.5 comes from inverting the ratio, dividing the SD by the difference.

Why is "+12" not the answer?

12 is the reference mean, not the Z score.

Why is "+14" not the answer?

14 is the raw weight and was not standardised.

What concept does this question test?

It tests Biostatistics: standard score in PSM. It states how many standard deviations the value lies from the mean, which is how growth standards are expressed.

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: standard score?

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.