Regression & correlation

In regression, the explanatory variable $x$ is used to predict the response variable $y$. The regression line is $\hat{y}=a+bx$, where $b=r\frac{s_y}{s_x}$ and $a=\bar{y}-b\bar{x}$. The correlation coefficient $r$ measures the strength and direction of a linear relationship between $-1$ and $1$.