simonwoo A density that looks like a normal density (but may or may not be exactly normal) is exactly symmetric about zero. (Symmetric means if you flip it around zero it looks the same.) What is its median? A The median must be 0. B We can't conclude anything about the median. C The median must be 1. D The median must be different from the mean. 选哪个对呢?
yanlinlin82 回复 第1楼 的 simonwoo：根据 http://en.wikipedia.org/wiki/Median#Medians_of_probability_distributions，概率分布的median有可能不唯一。 举个特殊的例子，假设某个分布的PDF如下： [data] f(x) = 1/2, if (1 < abs(x) < 2), = 0, otherwise [/data] 于是，在[-1,1] 之间的任何实数都可以是其median。 这样答案就很明白了。
