An Empirical Comparison of Formulas Evaluating Early Intervention Program Impact on Development

Early childhood special educators are increasingly challenged to demonstrate program impact. When appropriate control groups are not available, several investigators have proposed evaluating child developmental progress with various formulas which attempt to compensate for differential preintervention rates of development. This study applied a set of these formulas to Bayley data for three groups of handicapped infants. The results of the analyses indicate that these formulas fall into two classifications—those that measure rate of development and those that measure change in rate of development. Finally, issues and cautions in the use and interpretation of these formulas for evaluating program impact are discussed.