In a study of salt intake and systolic blood pressure across 50 districts, the Pearson correlation coefficient is calculated as r = -0.85. The correct interpretation is:

• A Strong positive linear association between the two variables
• B Weak negative association, salt intake explains about 15% of variation in blood pressure
• C A causal relationship has been demonstrated
• D Strong inverse linear association between salt intake and systolic blood pressure ✓

Explanation

Pearson r ranges from -1 to +1. A value of -0.85 indicates a strong inverse linear relationship: higher salt intake goes with lower blood pressure across these units. Correlation never establishes causation, so option C is wrong regardless of strength. Squaring r gives the coefficient of determination, 0.72 here, meaning about 72% of variation is explained, which rules out option B.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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