Fundamental Formulas

Symbol	Full Name	Formula
$\overline{x}$	Sample average of $x_{i}$	$\Sigma x_{i}$ / n
SSX or $ss_{XX}$	Corrected sum of squares for $x_{i}$	$\Sigma (x_{i} - \overline{x})^{2}$
		$\Sigma x_{i}^{2} - n \overline{x}^2$
		$\Sigma x_{i}^{2} - (\Sigma x_{i})^{2} / n$
$SD^{2}_{X}$	Sample variance of	$x_{i}$ $SXX / (n-1)$
$SD_{X}$ or $s$	Sample standard deviation	$\sqrt{ SXX / (n-1) }$
$SXY$ or $ss_{XY}$	Corrected sum of cross products	$\Sigma (x_{i} - \overline{x})(y_{i} - \overline{y})$
		$\Sigma x_{i} y_{i} - n \overline{x} \overline{y}$
$s_{XY}$	Sample covariance	$ss_{XY}/ (n-1)$
$r_{XY}$	Sample correlation	$ss_{XY} / \sqrt{ (ss_{XX})(ss_{YY}) }$
RMS	Root mean square error	$\sqrt{ \frac{1}{n_{i}} \Sigma (y_{i} - \hat{y}_{i})^{2}}$