Behavior Genetics, Vol. 8, No. 3, 1978 SHORT COMMUNICATION The Hawaii Family Study of Cognition: A Reply J. C. DeFries, 1 G. C. Ashton, 2 R. C. Johnson, 2 A. R. Kuse, 1 G. E. McClearn, 1 M. P. Mi, 2 M. N. Rashad, ~ S. G. Vandenberg, 1 and J. R. Wilson 1 Received 27 Nov. 1977--Final 2 Dec. 77 Differences in age and number of children tested per family between two ethnic groups (Americans of Japanese ancestry and Americans of European ancestry) have a trivial effect on differences in regressions of midchild on midparent for tests of specific cognitive abilities. Although the regression of offspring on midparent value is not a mathematical function of the spouse correlation, an empirical association between these two measures of familial resemblance is expected for characters with nonzero heritability. Such an association is reported for anthropometric characters. Since age effects contribute to the covariance of family members, age correction or family cognitive data is essential. KEY WORDS: assortative mating; cognitive ability; heritability; parent-offspring resemblance. In his critique of our 21/2-page note in Nature (DeFries et al., 1976), Kamin (1978) expresses concern about possible misinterpretation of the results and raises several issues which, in his opinion, cast doubt on their validity. We shall address these concerns and issues in the order in which they appear in his article. The results reported here are made possible by collaboration of a group of investigators (G. C. Ashton, R. C. Johnson, M. P. Mi, and M. N. Rashad at the University of Hawaii, and J. C. DeFries, G. E. McClearn, S. G. Vandenberg, and J. R. Wilson at the University of Colorado) supported by NSF Grant GB-34720 and Grant HD-06669 from the National Institute of Child Health and Human Development. 1 Institute for Behavioral Genetics, University of Colorado, Boulder, Colorado 80309. 2 Behavioral Biology Laboratory, University of Hawaii, Honolulu, Hawaii 96822. 281 0001-8244/78/0500-0281 $05.00/0 9 1978Plenum Publishing Corporation