Complex sentence: The square of the sample correlation coefficient is typically denoted r 2 and called the coefficient of determination, estimates the fraction of the variance in "Y" that is explained by "X" in a simple linear regression.
Split into simpler sentences: The square of the sample correlation coefficient is typically denoted r 2 and called the coefficient of determination. It estimates the fraction of the variance in "Y" that is explained by "X" in a simple linear regression.