Validity researchers typically work with nonrandom samples, membership in which depends in part on the exam score being investigated. In a study of the SAT's validity for freshman GPA at a particular college, for example, FGPA is not observed for the entire pool of potential applicants, but only for those who are admitted and enroll. This sample selection biases validity estimates. Corrections for restriction of range remedy the problem only when the exam score is the sole determinant of selection, and even then do not permit consistent estimation of the exam's incremental validity....