In the social sciences, evaluating the effectiveness of a program or intervention often leads researchers to draw causal inferences from observational research designs. Bias in estimated causal effects becomes an obvious problem in such settings. This article presents the Heckman Model as an approach sometimes applied to observational data for the…

An experiment in which 90 undergraduate students were tested on simple and complex versions of a word-span task with high and low frequency words suggests that both word knowledge and a content-free working memory play causal roles in the relationship between word span and higher level cognitive tasks. (SLD)

A longitudinal study was designed in 1986 to investigate why some high-ability minority students follow through with their plans to enroll in college and major in mathematics, science, or engineering (MSE) fields, while others do not. Data came from three sources: (1) 1985 Scholastic Aptitude Test (SAT) files of a sample of minority students…