Does the Sampling Method Produce the Negative Correlation of Mean IQ with Age Reported by Kennedy, van de Riet, and White?

An analysis of data reported by Kennedy, Van de Riet, and White suggests that their finding of a significant negative correlation of mean IQ with age for southeastern Negro children was produced by the sampling method. The small selected samples of children who were in the elementary school at the lower ages were probably more intelligent and those at the higher ages were probably less intelligent than the total population of Negro children at these age levels. The interpretation that a low mean IQ developed during the preschool years and remained stable during the elementary-school years suggests a need for research on factors related to intellectual development in the preschool years and for preschool programs designed to raise the level of intellectual functioning of culturally deprived children.