${Q}_{\frac {1}{2}}(x)={\begin{cases}x'_{\frac{n+1}{2}},&{n{\mbox{ is odd}}}\\{\frac {1}{2}}(x'_{\frac{n}{2}}+x'_{{\frac{n}{2}}+1}),&{n \mbox{ is even}}\end{cases}}$
- 中位数:${Q}_{\frac {1}{2}}(x)={\begin{cases}x'_{\frac{n+1}{2}},&{n \mbox{ is odd}}\\{\frac {1}{2}}(x'_{\frac{n}{2}}+x'_{{\frac{n}{2}}+1}),&{n \mbox{ is even}}\end{cases}}$