Biostatistics: linear regression: 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 · Biostatistics: linear regression

Sample item

A regression of systolic blood pressure (Y, mmHg) on age (X, years) in adults gives Y = 90 + 0.5X. What is the predicted systolic blood pressure of a 60-year-old?

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

The answer and the reasoning

B. 120 mmHg

The intercept is 90 and the regression coefficient (slope) is 0.5, meaning blood pressure rises by 0.5 mmHg for each year of age. For X = 60 the prediction is 90 + 0.5 x 60 = 120 mmHg. Predictions are reliable only within the range of observed ages.

Option by option

  • A. 150 mmHg

    This adds 60 to the intercept and ignores the slope of 0.5.

  • B. 120 mmHg (correct)

    Correct. 90 + 0.5 x 60 = 120.

  • C. 90.5 mmHg

    This substitutes X = 1 rather than 60.

  • D. 30 mmHg

    This is only the slope multiplied by age and leaves out the intercept.

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.

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Questions about this PSM question

What is the answer to this PSM question?

The best answer is B, 120 mmHg. The intercept is 90 and the regression coefficient (slope) is 0.

Why is "150 mmHg" not the answer?

This adds 60 to the intercept and ignores the slope of 0.5.

Why is "90.5 mmHg" not the answer?

This substitutes X = 1 rather than 60.

Why is "30 mmHg" not the answer?

This is only the slope multiplied by age and leaves out the intercept.

What concept does this question test?

It tests Biostatistics: linear regression in PSM. 5, meaning blood pressure rises by 0.5 mmHg for each year of age. For X = 60 the prediction is 90 + 0.5 x 60 = 120 mmHg. Predictions are reliable only within the range of observed ages.

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 Biostatistics: linear regression?

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.