Biostatistics: coefficient of determination: 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: coefficient of determination

Sample item

In a sample the correlation coefficient between daily salt intake and systolic blood pressure is 0.6. What proportion of the variation in systolic blood pressure is statistically accounted for by salt intake?

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

The answer and the reasoning

D. 36%

The coefficient of determination is the square of the correlation coefficient. Here r squared = 0.6 x 0.6 = 0.36, so 36% of the variation in blood pressure is explained by its linear relationship with salt intake. Correlation by itself does not prove causation.

Option by option

  • A. 77%

    This is the square root of 0.6, the wrong direction of calculation.

  • B. 60%

    This treats r itself as the proportion explained, forgetting to square it.

  • C. 40%

    This is 1 minus r, which is not the proportion of variance explained.

  • D. 36% (correct)

    Correct. Squaring r gives 0.36.

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 D, 36%. The coefficient of determination is the square of the correlation coefficient.

Why is "77%" not the answer?

This is the square root of 0.6, the wrong direction of calculation.

Why is "60%" not the answer?

This treats r itself as the proportion explained, forgetting to square it.

Why is "40%" not the answer?

This is 1 minus r, which is not the proportion of variance explained.

What concept does this question test?

It tests Biostatistics: coefficient of determination in PSM. Here r squared = 0.6 x 0.6 = 0.36, so 36% of the variation in blood pressure is explained by its linear relationship with salt intake. Correlation by itself does not prove causation.

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: coefficient of determination?

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.