Epidemiology: attrition bias: 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 · Epidemiology: attrition bias

Sample item

In a ten-year cohort of alcohol use and liver disease, 30% of participants are lost to follow-up, and losses are much higher among heavy drinkers who moved away or died of other causes. Which problem does this introduce?

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

The answer and the reasoning

D. Selection bias from differential loss to follow-up

Differential loss to follow-up, also called attrition bias, makes the remaining groups unlike the original ones and biases the measured association. Recall bias concerns memory of past exposure. Length-time bias concerns screening, and the Hawthorne effect concerns behaviour changing under observation.

Option by option

  • A. Recall bias

    Recall bias needs participants to report past exposures, which a prospective cohort largely avoids.

  • B. Hawthorne effect

    The Hawthorne effect is a change in behaviour caused by being observed.

  • C. Length-time bias

    Length-time bias applies to screen-detected disease and not to cohort attrition.

  • D. Selection bias from differential loss to follow-up (correct)

    Correct. Unequal loss of participants by exposure is attrition-related selection bias.

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, Selection bias from differential loss to follow-up. Differential loss to follow-up, also called attrition bias, makes the remaining groups unlike the original ones and biases the measured association.

Why is "Recall bias" not the answer?

Recall bias needs participants to report past exposures, which a prospective cohort largely avoids.

Why is "Hawthorne effect" not the answer?

The Hawthorne effect is a change in behaviour caused by being observed.

Why is "Length-time bias" not the answer?

Length-time bias applies to screen-detected disease and not to cohort attrition.

What concept does this question test?

It tests Epidemiology: attrition bias in PSM. Recall bias concerns memory of past exposure. Length-time bias concerns screening, and the Hawthorne effect concerns behaviour changing under observation.

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: attrition bias?

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.