从等号右边的表达式很容易知道符号的意义，用作离差平方和及离差积和的简单记号。x的离差平方和记作圆盟sxx，y的离差平方和记作骏口syy，x和y的离差积和记作sxy。
1.缩小x的range 2.添加influential observation周围的点 Nonetheless, we may need either to remove it—thus limiting the analysis toOrions between 4 and 7 years old—or to obtain additional data on 2- and 3-year-oldOrions so that the regression analysis is not so dependent on one data point ...