Biostatistics: interpreting a regression coefficient: 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: interpreting a regression coefficient

Sample item

A regression of systolic blood pressure on age in adults gives the equation: systolic pressure = 90 + 0.8 x age. How should the coefficient 0.8 be interpreted?

A80% of the variation in pressure is explained by ageBSystolic pressure rises by 0.8 mmHg for each 10 years of ageCMean systolic pressure rises by 0.8 mmHg for each extra year of ageDThe correlation between age and pressure is 0.8

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

The answer and the reasoning

C. Mean systolic pressure rises by 0.8 mmHg for each extra year of age

In a simple linear regression the coefficient of the independent variable is the slope, the average change in the dependent variable for a one-unit increase in the predictor. Here that is 0.8 mmHg per year of age. The proportion of variance explained is given by the square of the correlation coefficient, which is a different quantity.

Option by option

A. 80% of the variation in pressure is explained by age
Variance explained is given by r squared and not by the slope.
B. Systolic pressure rises by 0.8 mmHg for each 10 years of age
The unit of change is one year, not ten years.
C. Mean systolic pressure rises by 0.8 mmHg for each extra year of age (correct)
Correct. The slope gives the mean change per unit of the predictor.
D. The correlation between age and pressure is 0.8
The slope depends on the units of both variables and is not the correlation coefficient.

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.

Questions about this PSM question

What is the answer to this PSM question?

The best answer is C, Mean systolic pressure rises by 0.8 mmHg for each extra year of age. In a simple linear regression the coefficient of the independent variable is the slope, the average change in the dependent variable for a one-unit increase in the predictor.

Why is "80% of the variation in pressure is explained by age" not the answer?

Variance explained is given by r squared and not by the slope.

Why is "Systolic pressure rises by 0.8 mmHg for each 10 years of age" not the answer?

The unit of change is one year, not ten years.

Why is "The correlation between age and pressure is 0.8" not the answer?

The slope depends on the units of both variables and is not the correlation coefficient.

What concept does this question test?

It tests Biostatistics: interpreting a regression coefficient in PSM. Here that is 0.8 mmHg per year of age. The proportion of variance explained is given by the square of the correlation coefficient, which is a different quantity.

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: interpreting a regression coefficient?

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.