A correlation between reading and math achievement scores on a national standardized test for first graders indicates a correlation of r = .90. How much variance do these scores share?
A) 30%
B) 45%
C) 81%
D) 90%

Question

Quizplus · Accepted Answer

The correlation coefficient (r) measures the strength and direction of the relationship between two variables. The coefficient of determination (r^2) indicates the proportion of variance shared by the two variables. To calculate r^2, we square the correlation coefficient: r^2 = 0.9^2 = 0.81, or 81%. Therefore, choice C is correct as the two variables share 81% variance.

A Correlation Between Reading and Math Achievement Scores on a National