Which of the following is not a correlation coefficient type?

• A. R-squared
• B. Pearson correlation
• C. Spearman correlation
• D. Kendall tau

Answer: (A)

Correlation coefficients quantify the strength and direction of association between two variables. Pearson correlation measures linear relationships and ranges from -1 to 1; Spearman and Kendall tau measure monotonic or rank-based associations, also typically ranging between -1 and 1. R-squared, the coefficient of determination, is a regression statistic that describes the proportion of the variance in the dependent variable explained by the model. It reflects how well the model fits the data rather than directly describing the strength or direction of a two-variable relationship. In simple linear regression, R-squared relates to Pearson r (it is the square of r), but as a standalone statistic it is not a correlation coefficient type. Therefore, it is the choice that is not a correlation coefficient type.