A study finds a correlation coefficient of r = -0.85 between duration of exclusive breastfeeding and incidence of diarrhoea episodes in infants. The correct interpretation is:
- A Weak negative correlation
- B Strong positive correlation
- C Strong negative correlation, longer breastfeeding associated with fewer diarrhoea episodes ✓
- D Breastfeeding causes a reduction in diarrhoea by 85 percent
Correct answer: C. Strong negative correlation, longer breastfeeding associated with fewer diarrhoea episodes
Explanation
An absolute value above roughly 0.7 denotes strong correlation, and the negative sign indicates that as breastfeeding duration rises, diarrhoea episodes fall. Option D confuses correlation with causation and misreads r as a percentage effect size; a correlation coefficient never quantifies magnitude of causal effect. Option A wrongly calls a high absolute value weak. Also note correlation alone cannot establish causality despite the plausible biological mechanism.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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