Pearson's correlation coefficient (r) ranges from -1 to +1. An r value of -0.85 between hours of physical activity and blood glucose levels indicates:
- A Strong positive correlation — blood glucose increases with activity
- B Weak inverse relationship with poor statistical significance
- C Strong negative correlation — blood glucose decreases as activity increases ✓
- D No meaningful correlation despite statistical significance
Correct answer: C. Strong negative correlation — blood glucose decreases as activity increases
Explanation
Pearson's r of -0.85 indicates a strong negative (inverse) correlation — as hours of physical activity increase, blood glucose levels decrease. The sign indicates direction (positive = same direction, negative = inverse), and the absolute value indicates strength (|r| > 0.7 = strong; 0.4-0.7 = moderate; < 0.4 = weak). The coefficient of determination (r²) = 0.72, meaning physical activity explains 72% of the variance in blood glucose levels.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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