The article explains how to deal with a common problem in research called endogeneity by using instrumental variables. It shows how to use these variables to figure out cause and effect relationships in data. The article also talks about a method called the Heckman two-step procedure and provides tests and methods to check if the data is reliable. The author even gives commands for using these techniques in a program called STATA. Overall, this article helps researchers understand and fix problems in their data to make their findings more accurate.