A study reports a Pearson correlation coefficient (r) of -0.78 between daily aerobic exercise minutes and fasting blood glucose in diabetic patients. The BEST interpretation is:
- A Moderate positive correlation; 78% of the variation in blood glucose is explained by exercise
- B Weak negative correlation; the relationship is not clinically meaningful
- C Strong negative correlation; as exercise increases, blood glucose tends to decrease ✓
- D Causation is established — exercise directly lowers blood glucose
Correct answer: C. Strong negative correlation; as exercise increases, blood glucose tends to decrease
Explanation
Pearson's r = −0.78 indicates a strong negative linear correlation — as exercise duration increases, fasting blood glucose tends to decrease. The coefficient of determination (r²) = 0.61, meaning approximately 61% of variance in blood glucose is explained by exercise. Correlation does not prove causation. A value of −0.78 is not 'weak' — r values above 0.6 (in absolute terms) are generally considered strong.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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