Econometric Analysis of Cross Section and Panel Data by Jeffrey M. Wooldridge这本书中的Example 7.3 on page 165是如何从解释变量平方项回归结果中判定拐点的位置不是很明白,具体问题就是下面黄色这句话怎么来的?
回归数据及命令如下: use http://www.stata.com/data/jwooldridge/eacsap/fringe回归命令如下: sureg ( hrearn educ exper expersq tenure tenuresq union south nrtheast nrthcen married white male) ( hrbens educ exper expersq tenure tenuresq union south nrtheast nrthcen married white male)
回归结果如下(expersq这行):