Correlation analysis tests collinearity between vari- ables. Collinearity doesn’t exist if the correlation coeffi- cient is not greater than 0.8, according to the study of Hossain, Perera and Rahman [1]. Analysis shows there is some correlation between variables, but the largest cor- relation coefficient is 0.462 (between directors’ educa- tion level and supervisors’ education level), which is less than 0.8. Thus variables are unlikely collinear. To further illustrate the problem, we also test tolerance and variance inflation factor. The minimum of tolerance is 0.657 (the