The prediction that differences in incomes of high school and college graduates will not change is tested by applying standard statistical procedures to data describing actual income differences. Data from the United States Bureau of the Census describe annual incomes of men twenty-five years old and older during 1956-75. Report 1 displays results…

The accuracy with which regression models estimate treatment effects is dependent upon a number of conditions. The stability of the regression line (a function of sample size and correlation between pretest and posttest) is said to be the most important of these conditions. The utility of regression models is proportional to the size of the…