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The Personalities of Twins: Just Ordinary Folks

Published online by Cambridge University Press:  21 February 2012

Wendy Johnson ,
Robert F. Krueger ,
Thomas J. Bouchard Jr.  and
Matt McGue
Wendy Johnson*
Affiliation:
University of Minnesota,Twin Cities. [email protected]
Robert F. Krueger
Affiliation:
University of Minnesota,Twin Cities.
Thomas J. Bouchard Jr.
Affiliation:
University of Minnesota,Twin Cities.
Matt McGue
Affiliation:
University of Minnesota,Twin Cities.
*
*Address for correspondence: Wendy Johnson, University of Minnesota, Twin Cities, 14811 Stone Road, Minnetonka, MN 55391, USA.

Abstract

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Twin studies have demonstrated that personality traits show moderate genetic influence. The conclusions drawn from twin studies rely on the assumptions that twins are representative of the population at large and that monozygotic and dizygotic twins are comparable in every way that might have bearing on the traits being studied. To evaluate these assumptions, we used Multidimensional Personality Questionnaire (MPQ) data from three samples drawn from the Minnesota Twin Registry (totaling 12,971 respondents) to examine the effect sizes associated with mean differences on the 11 MPQ scales and 3 higher-order MPQ factors for singletons versus twins and MZ twins versus DZ twins. The singletons in the samples were family members of the participating twins. We also used ratios of scale variances to examine the significance of variance differences. The only mean or variance difference replicated across all three samples was greater Social Closeness (about .1 standard deviation) for twins than for singletons. This difference was obtained for both males and females. It would appear that, with respect to personality, twins are not systematically different from other people. Our results also highlight the importance of replication in psychological research because each of our large samples showed differences not replicated in other samples.

Type
Articles
Information
Twin Research and Human Genetics , Volume 5 , Issue 2 , 01 April 2002 , pp. 125 - 131
Copyright
Copyright © Cambridge University Press 2002