We are given the following and asked how much of RBC stock’s excess return variation can be attributed to company specific risk.

Regression Statistics Multiple R = 0.7131 R-squared = 0.5086 Standard error of estimate = 0.0269 Observations= 60

This is the solution:

The R^{2} in this regression is 0.5086. This result suggests that about 51 percent of the total variation in the excess return to RBC stock (the return to RBC above the risk-free rate) can be explained by excess return to the market portfolio. The remaining 49 percent of RBC stock’s excess return variation is the nonsystematic component, which can be attributed to company-specific risk.

Why not use the Standard Error of Estimate to find the SSE which is related to the errors of the regression?