regress

本义：to go back; move backward；to return to a previous, usually worse or less developed state

引申到：to have a tendency to approach or go back to a statistical mean。

regress还有另一个意义：reasoning backward from an effect to a cause（由果及因的“逆推理”）

最一般的OLS是基于（条件）均值的分析。寻找（回溯）变量间在均值意义上的关系：regress。