In a community study, the correlation coefficient between monthly household income and per capita sugar consumption is r = -0.90. The correct interpretation is:

• A Ninety percent of variation in sugar consumption is explained by income
• B Lower income causes higher sugar consumption
• C There is a weak inverse relationship between the variables
• D Higher income is strongly associated with lower sugar consumption ✓

Explanation

The sign shows direction and the magnitude shows strength, so r = -0.90 indicates a strong inverse linear association. Correlation never establishes causation, which eliminates option B. Option A confuses r with the coefficient of determination r squared, which here would be about 0.81, meaning roughly 81 percent of the variance in one variable is explained by the other. Option C is wrong because 0.90 denotes a strong, not weak, relationship.

Reference: Mahajan's Methods in Biostatistics for Medical Students and Research Workers, 9th ed.

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