几种偏差

推荐系统中的：

position bias：

推荐系统中，item在靠前的，更有几率被点击

selection bias：

(wiki: ) Selection bias is the bias introduced by the selection of individuals, groups, or data for analysis in such a way that proper randomization is not achieved, thereby failing to ensure that the sample obtained is representative of the population intended to be analyzed.

例子：统计地铁上人的购票率

popularity bias：马太效应