Epidemiology: healthy worker effect: 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: healthy worker effect

Sample item

A cohort of 2000 men employed in a stone-crushing unit is followed for 15 years. Their all-cause standardised mortality ratio compared with the general male population is 0.8, although several cases of silicosis are documented. Which phenomenon best explains the low all-cause SMR?

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

The answer and the reasoning

C. Healthy worker effect, a selection bias that makes workers look healthier than the general population

Workers are selected for employment partly on health, and those who fall ill tend to leave work, so working cohorts usually have lower overall mortality than the general population. This can mask the true occupational hazard, which is why an internal comparison group of less exposed workers is preferred. The documented silicosis shows that the hazard is real.

Option by option

  • A. Neyman bias arising from the exclusion of cases with short survival

    Neyman (prevalence-incidence) bias occurs in prevalence studies that miss rapidly fatal or short-duration cases.

  • B. Lead-time bias arising from earlier detection of disease

    Lead-time bias applies to survival after screening-detected disease and not to cohort SMRs.

  • C. Healthy worker effect, a selection bias that makes workers look healthier than the general population (correct)

    Selection of fit people into employment lowers all-cause SMR and can hide an occupational hazard.

  • D. Recall bias arising from retrospective collection of exposure history

    Recall bias concerns inaccurate memory of past exposure and does not alter an SMR from employment records.

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 C, Healthy worker effect, a selection bias that makes workers look healthier than the general population. Workers are selected for employment partly on health, and those who fall ill tend to leave work, so working cohorts usually have lower overall mortality than the general population.

Why is "Neyman bias arising from the exclusion of cases with short survival" not the answer?

Neyman (prevalence-incidence) bias occurs in prevalence studies that miss rapidly fatal or short-duration cases.

Why is "Lead-time bias arising from earlier detection of disease" not the answer?

Lead-time bias applies to survival after screening-detected disease and not to cohort SMRs.

Why is "Recall bias arising from retrospective collection of exposure history" not the answer?

Recall bias concerns inaccurate memory of past exposure and does not alter an SMR from employment records.

What concept does this question test?

It tests Epidemiology: healthy worker effect in PSM. This can mask the true occupational hazard, which is why an internal comparison group of less exposed workers is preferred. The documented silicosis shows that the hazard is real.

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: healthy worker effect?

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.