sperman係數

https://baike.baidu.com/item/spearman%E7%9B%B8%E5%85%B3%E7%B3%BB%E6%95%B0/7977847?fr=aladdin

https://blog.csdn.net/sinat_24143931/article/details/78798630

https://blog.csdn.net/wsywl/article/details/5859751