Epidemiology: ecological fallacy: 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: ecological fallacy

Sample item

Using district-level data, an analyst finds that districts with higher average sale of packaged snacks have higher rates of childhood obesity, and concludes that children who eat these snacks become obese. Which error is this conclusion most likely to involve?

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

The answer and the reasoning

D. Ecological fallacy

In an ecological study the unit of analysis is a group, so an association at group level may not hold for individuals. Inferring individual-level causation from aggregate data is the ecological fallacy. The same districts may differ in income, urbanisation and activity levels, and the snack eaters need not be the obese children.

Option by option

  • A. Recall bias

    Recall bias occurs when cases and controls remember past exposures differently, which is not relevant to aggregate data.

  • B. Lead-time bias

    Lead-time bias applies to screening, where earlier diagnosis seems to lengthen survival.

  • C. Berkson's bias

    Berkson's bias arises when hospital-based cases and controls have different admission rates.

  • D. Ecological fallacy (correct)

    Correct. Group-level correlation has been wrongly applied to individual children.

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, Ecological fallacy. In an ecological study the unit of analysis is a group, so an association at group level may not hold for individuals.

Why is "Recall bias" not the answer?

Recall bias occurs when cases and controls remember past exposures differently, which is not relevant to aggregate data.

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

Lead-time bias applies to screening, where earlier diagnosis seems to lengthen survival.

Why is "Berkson's bias" not the answer?

Berkson's bias arises when hospital-based cases and controls have different admission rates.

What concept does this question test?

It tests Epidemiology: ecological fallacy in PSM. Inferring individual-level causation from aggregate data is the ecological fallacy. The same districts may differ in income, urbanisation and activity levels, and the snack eaters need not be the obese children.

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: ecological fallacy?

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.