如题，有一篇英文文献原文为：In the first stage, we run 5000 probit equation on Core NTBs (one for each product) explained by the instruments discussed above, to obtain the Mills ratio (the ratio of the probability density function and the cumulative density function of each observation). The second stage equation adds the Mills ratio of the probit model describing the……
现在我想模仿作者的做法，用probit模型做一个回归分析，但我对probit模型了解不够深入，请问如何在stata中求出Mills Ratio？应该使用什么命令？另外作者用的是Heckman 2阶段回归方法，请问命令该如何写？（如果命令中需要写变量，那么因变量用y表示，自变量用x1、x2……表示）