Biostatistics: validity and reliability: 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: validity and reliability

Sample item

A weighing scale gives the same reading each time for a child but always reads 1 kg too high. The scale is:

ABoth valid and reliableBReliable but not validCValid but not reliableDNeither valid nor reliable

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

The answer and the reasoning

B. Reliable but not valid

Consistent results across repeated measurements indicate reliability (precision), while a constant offset from the true value means a lack of validity (accuracy).

Option by option

A. Both valid and reliable
A systematic error makes it invalid.
B. Reliable but not valid (correct)
Correct. It is consistent but systematically wrong.
C. Valid but not reliable
Validity cannot hold with a systematic error.
D. Neither valid nor reliable
It is reliable because readings are repeatable.

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 B, Reliable but not valid. Consistent results across repeated measurements indicate reliability (precision), while a constant offset from the true value means a lack of validity (accuracy).

Why is "Both valid and reliable" not the answer?

A systematic error makes it invalid.

Why is "Valid but not reliable" not the answer?

Validity cannot hold with a systematic error.

Why is "Neither valid nor reliable" not the answer?

It is reliable because readings are repeatable.

What concept does this question test?

It tests Biostatistics: validity and reliability in PSM. The correct option holds because: Correct. It is consistent but systematically wrong.

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: validity and reliability?

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.