Adjustment of twin data for the effects of age and sex
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For most psychological, physiological, and medical variables there are substantial age and sex effects. In assessing twin similarity for these variables, one can either fail to adjust for the effects of age and sex, adjust for these effects using normative data, or use information in the twin sample to define an age-sex adjustment. It is shown that failing to correct for age and sex effects when they exist will result in overestimation of the twin intraclass correlation. Using normative data to define an age-sex adjustment will also result in overestimation of the twin intraclass correlation, although the magnitude of this overestimation is slight for moderate-sized normative samples and virtually nonexistent for large normative samples. Using a twin-based age-sex adjustment will lead to an underestimation of the twin intraclass correlation, but this underestimation can be corrected for through proper specification of the degrees of freedom for the between-pairs mean square. Illustration of the effects of age-sex adjustment are provided as well as the results of a computer simulation comparison of the various approaches. It is concluded that, even with moderately sized samples, the effects of age and sex can best be adjusted for through a twin-based approach.
- Birron, J. E., and Schaie, K. W. (1977).Handbook of the Psychology of Aging, Van Norstrand Reinhold, New York.
- Bouchard, T. J., Heston, L., Eckert, E., Keyes, M., and Resnick, S. (1981). In Gedda, L., Parisi, P., and Nance, W. E. (eds.),Twin Research 3: Intelligence Personality, Development, Alan R. Liss, New York.
- Finch, C. E., and Hayflick, L. (1977).Handbook of the Biology of Aging, Van Norstrand Reinhold, New York.
- Fisher, R. A. (1921). On the probable error of a coefficient of correlation deduced from a small sample.Metron 1:1–32.
- Garai, J. E., and Scheinfeld, A. (1968). Sex differences in mental and behavioral traits.Genet. Psychol. Monogr. 77:169–299.
- Haggard, E. A. (1958).Intraclass Correlation and the Analysis of Variance, Dryden, New York.
- Hyde, J. S. (1981). How large are cognitive gender differences: A meta analysis using ω2 and d.Am. Psychol. 36:892–901.
- IMSL Inc. (1979).IMSL Library Reference Manual Edition 7, IMSL Inc., Houston, Tex.
- Maccoby, E., and Jacklin, C. N. (1974).The Psychology of Sex Differences, Stanford University Press, Stanford, Calif.
- Wilson, J. R., and Vandenberg, S. G. (1978). Sex differences in cognition: Evidence from the Hawaii Family Study. In McGill, T. E., Dewsbury, D. A., and Sachs, B. D. (eds.),Sex and Behavior, Plenum Press, New York, pp. 317–355.
- Wilson, J. R., DeFries, J. C., McClearn, G. E., Vandenberg, S. G., Johnson, R. C., Mi, M. P., and Rashad, M. N. (1975). Cognitive abilities: Use of family data as a control to assess sex and age differences in two ethnic groups.Int. J. Aging Hum. Devel. 6:261–276.
- Adjustment of twin data for the effects of age and sex
Volume 14, Issue 4 , pp 325-343
- Cover Date
- Print ISSN
- Online ISSN
- Kluwer Academic Publishers-Plenum Publishers
- Additional Links
- twin data analysis
- intraclass correlation
- age-sex effects
- Author Affiliations
- 1. Division of Biostatistics, Washington University School of Medicine, 4566 Scott Avenue, Box 8067, 63110, St. Louis, Missouri
- 2. Department of Psychology, University of Minnesota, Elliott Hall, 75 East River Road, 55455, Minneapolis, Minnesota