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…

The second of two reports on a national evaluation of the immediate effects of Project Head Start describes the characteristics of children, families and programs in samples of full-year classes operating in 1966-67 and 1967-68. No control groups were used; comparisons were made within the Head Start sample to see what kinds of classroom…

The first of two reports of a national evaluation of the immediate effects of Project Head Start describes the characteristics of children, families and programs in samples of full-year classes operating in 1968-69. The study identifies changes associated with Head Start participation and the conditions under which these changes were greatest. No…