Study designs: 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 · Study designs

Sample item

What is confounding in an observational study?

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

The answer and the reasoning

A. Distortion of an exposure-outcome association by a related third factor

Confounding occurs when another factor is associated with both the exposure and outcome and is not on the causal pathway, creating or masking an apparent association unless addressed by design or analysis.

Option by option

  • A. Distortion of an exposure-outcome association by a related third factor (correct)

    Correct: a related third factor can distort the observed association.

  • B. Selection bias from non-comparable enrollment

    Selection bias arises from how participants are enrolled or retained, not from a third factor mixing effects.

  • C. Random sampling variation around an estimate

    Sampling variation is random error and does not require a third factor related to exposure and outcome.

  • D. Measurement error from a miscalibrated instrument

    Miscalibration causes information error rather than confounding by a covariate.

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 A, Distortion of an exposure-outcome association by a related third factor. Confounding occurs when another factor is associated with both the exposure and outcome and is not on the causal pathway, creating or masking an apparent association unless addressed by design or analysis.

Why is "Selection bias from non-comparable enrollment" not the answer?

Selection bias arises from how participants are enrolled or retained, not from a third factor mixing effects.

Why is "Random sampling variation around an estimate" not the answer?

Sampling variation is random error and does not require a third factor related to exposure and outcome.

Why is "Measurement error from a miscalibrated instrument" not the answer?

Miscalibration causes information error rather than confounding by a covariate.

What concept does this question test?

It tests Study designs in PSM. The correct option holds because: Correct: a related third factor can distort the observed association.

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 Study designs?

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.