In the last post "The Difference of Occupation Choice Among Graduates with Different Majors and Degrees", I built a logistic model with log of salary as one of the independent variable. But we will concern about the endogeneity of it, because the salary may related to other unincluded variables that may affect the probability of working at education institute, and moreover, as a current salary, the occupation itself may affect the salary. So some instruments are needed to solve the possible endogeneity problem in the regression analysis. In the dataset, a variable "satis" measuring the satisfaction of salary seems to be a good possible instrument. For this variable, 4 means very satisfied, 3 means somewhat satisfied, 2 means somewhat unsatisfied, and 1 means very unsatisfied. Let's firstly take a look at the model without using IV. The dependent variable is whether working at education institutes, and independent variables are degree, major, number of years af...