(統計)(敘述統計)偏態係數(skewness coefficinet)，峰態係數(kurtosis coefficinet)

偏態係數(skewness coefficinet)

$\alpha_1=\cfrac{\frac{\displaystyle\sum_{i=1}^{N}(X_i-\mu)^3}{N}}{\sigma^3}$

$\alpha_1= $$\left\{
\begin{array}{c}
 >0,右偏 \\ =0,對稱 \\  <0,左偏
\end{array}
\right.  $

峰態係數(kurtosis coefficinet)

$\alpha_2=\cfrac{\frac{\displaystyle\sum_{i=1}^{N}(X_i-\mu)^4}{N}}{\sigma^4}$

$\alpha_2= $$\left\{
\begin{array}{c}
 >3,高峽峰 \\ =0,常態峰 \\  <3,低闊峰
\end{array}
\right.  $

特例:t分配為低闊峰，峰態係數>3