## 6.11 Purity of Coefficients

• $$r = \frac{\sum (x_i - \bar x)(y_i - \bar y)}{\sqrt{\frac{\sum(x_i - \bar x)^2}{n}\frac{\sum(y_i - \bar y)^2}{n}}}$$
• $$\rho = 1- \frac{6 \sum d_i^2}{n(n^2-1)}$$
• b or $$\beta$$

To be continued …