Chandra A. Reynolds1, Margaret Gatz1, Nancy L. Pedersen2
Both stability and change in cognitive abilities in older adults have been documented in recent twin studies. The present study extends previous work by applying biometrical growth models that account for changes in level and rate of change in a sample of 788 twins from the Swedish Adoption/Twin Study of Aging (Pedersen, N. L., McClearn, G. E., Plomin, R., Nesselroade, J. R., Berg, S., and deFaire, U., 1991, Acta Genetica Medicae et Gemmellologiae, 40, 7-20) and the Study of Dementia in Swedish Twins (Gatz, M., Pedersen, N. L., Berg, S., Johansson, B., Johansson, K., Mortimer, J. A., Posner, S. F., Viitanen, M., Winblad, B., and Ahlbom, A.,1997, Journal of Gerontology: Medical Sciences, 52A, M117- M125). The models considered allow for testing effects and make use of methods that allow for missing data. Cognitive tests were administered to each individual from one to six times between 1985 and 1995 with either three years or 18 months between testing occasions. Initial analyses indicate lower familiality for rates of change than for level across six cognitive tests: WAIS Information, Koh's Block Design, Digit Span (Forward and Backward), Thurstone's Picture Memory, and Symbol Digit. Of the tests considered, Symbol Digit exhibited the largest familiality for rate of decline.
Address: Department of Psychology, University of Southern California, Los Angeles, CA 90089-1061., E-mail: reynold@rcf.usc.edu; Phone: (213) 740-0864; FAX: (213) 746-5994.
1Department of Psychology, University of Southern California, Los Angeles, CA 90089-1061. 2Division of Epidemiology, Institute of Environmental Medicine, The Karolinska Institute, P.O. Box 210, 17177 Stockholm 3Supported by NIH grants AG10175, AG04563 and AG08724.