Epidemiology: 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 · Epidemiology

Sample item

What is effect modification?

ARandom error from small sample sizeBFailure to recruit controlsCExposure effect differs across levels of a third variableDA test result changing after calibration

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

The answer and the reasoning

C. Exposure effect differs across levels of a third variable

Effect modification occurs when an exposure has meaningfully different associations with an outcome in different subgroups, such as by age or sex.

Option by option

A. Random error from small sample size
Random error affects precision, not subgroup effect structure.
B. Failure to recruit controls
Control recruitment is a selection issue.
C. Exposure effect differs across levels of a third variable (correct)
Correct: subgroup-specific effects indicate interaction or modification.
D. A test result changing after calibration
Calibration concerns measurement accuracy.

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 C, Exposure effect differs across levels of a third variable. Effect modification occurs when an exposure has meaningfully different associations with an outcome in different subgroups, such as by age or sex.

Why is "Random error from small sample size" not the answer?

Random error affects precision, not subgroup effect structure.

Why is "Failure to recruit controls" not the answer?

Control recruitment is a selection issue.

Why is "A test result changing after calibration" not the answer?

Calibration concerns measurement accuracy.

What concept does this question test?

It tests Epidemiology in PSM. The correct option holds because: Correct: subgroup-specific effects indicate interaction or modification.

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 Epidemiology?

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.