In a community study, the correlation coefficient between weekly hours of vigorous exercise and resting systolic blood pressure is r = -0.82. The correct interpretation is:
- A Exercise causes a fall in blood pressure
- B Strong inverse association, but causation cannot be inferred ✓
- C Weak negative association with high statistical significance
- D 82% of variation in blood pressure is explained by exercise
Correct answer: B. Strong inverse association, but causation cannot be inferred
Explanation
A correlation coefficient of -0.82 indicates a strong linear inverse relationship: more exercise tends to accompany lower systolic pressure. Correlation quantifies association only and can never establish causation, which requires experimental or rigorous observational designs controlling confounding. Option D confuses r with the coefficient of determination, which would be r squared, about 0.67, not 0.82.
Reference: Mahajan's Methods in Biostatistics for Medical Students and Research Workers, 9th ed.
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