The construction and utility of three indexes of intellectual achievement : an intellectual-development (ID) index, a socio-intellectual-status (SIS) index, a differential-intellectual-development (DID) index, U.S. children and youths, 6-17 years / - Dupuy, Harold J. (U.S. Dept. of Health, Education, and Welfare, Public Health Service, Health Resources Administration, National Center for Health Statistics, 1977)