STATA problem: The data set "NSW.dta" on Courseworks contains observations from The National Supported Work Demonstration (NSW), which was a temporary employment program designed to help disadvantaged workers lacking basic job skills move into the labor market by giving them work experience and counseling in a sheltered environment. In this program, some workers were assigned to the Treatment group treat==1 and were given assistance, while others were assigned to a Control group treat==0. The workers' real earnings in 1978, at the end of the program, are given by the variable re78, and their earnings in 1975, before the beginning of the program, are given by the variable re75