因果分支的诞生

52 The slope could never be greater than 1;if it were,the sons of tall fathers would be taller on average,and the sons of shorter fathers would be short.

52 For Pearson,especially,the slippery old concepts of cause and effect seemed outdated and unscientific,compared to the mathematically clear and precise concept of a correlation coefficient.

50~52 Gilton继续在身高上做文章，发现其实无论用儿子的身高预测父亲的身高还是反过来，都是可行的。这让Gilton意识到在回归曲线上找因果性是不可行的。
在相关性中，哪个变量作为证据哪个变量作为对象，对应的不同的回归曲线。