A study reports a correlation coefficient between salt intake and systolic blood pressure as r = -0.82 with p < 0.001. The correct interpretation is:
- A Higher salt intake causes lower blood pressure
- B The association is weak because the sign is negative
- C There is a strong negative linear association, but causation cannot be inferred ✓
- D Salt intake explains 82% of the variation in blood pressure
Correct answer: C. There is a strong negative linear association, but causation cannot be inferred
Explanation
The strength of a correlation is given by its absolute value, so 0.82 indicates a strong relationship regardless of sign, killing option B. A negative sign means one variable falls as the other rises. Correlation never establishes causation, which kills option A. The coefficient of determination is r squared, that is about 67%, not 82%, so option D confuses r with r squared.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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