In the simple regression model, ŷ = 21 − 5x, if the coefficient of determination is 0.81, we can say that the coefficient of correlation between y and x is 0.90.

Question

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The coefficient of determination (R^2) is the square of the coefficient of correlation (r). If R^2 = 0.81, then r = ±0.9. However, since the slope is negative (-5), the correct correlation coefficient is -0.9, not 0.90.

In the Simple Regression Model, ŷ = 21 − 5x