Epidemiology: overmatching in case-control studies: 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: overmatching in case-control studies

Sample item

In a case-control study of a solvent exposure and bladder cancer, controls were matched to cases on the same factory, which strongly determines exposure. The exposure distribution in cases and controls became nearly identical. What problem has occurred?

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

The answer and the reasoning

D. Overmatching

Matching on a factor that is strongly associated with the exposure makes the controls resemble the cases in exposure, which hides a real association. This is overmatching, and it biases the odds ratio toward the null and loses efficiency. Only established confounders should be matched.

Option by option

  • A. Recall bias

    Recall bias arises from differing memory of past exposures between cases and controls.

  • B. Surveillance bias

    Surveillance bias comes from more intensive detection in exposed people.

  • C. Interviewer bias

    Interviewer bias arises from differential probing by the interviewer.

  • D. Overmatching (correct)

    Correct. Matching on a determinant of exposure removes the exposure contrast.

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 D, Overmatching. Matching on a factor that is strongly associated with the exposure makes the controls resemble the cases in exposure, which hides a real association.

Why is "Recall bias" not the answer?

Recall bias arises from differing memory of past exposures between cases and controls.

Why is "Surveillance bias" not the answer?

Surveillance bias comes from more intensive detection in exposed people.

Why is "Interviewer bias" not the answer?

Interviewer bias arises from differential probing by the interviewer.

What concept does this question test?

It tests Epidemiology: overmatching in case-control studies in PSM. This is overmatching, and it biases the odds ratio toward the null and loses efficiency. Only established confounders should be matched.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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: overmatching in case-control studies?

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.