Minnesota Twin Family Study

The Minnesota Twin Family Study (or MTFS) is a longitudinal study of twins conducted by researchers at the University of Minnesota - Twin Cities. It seeks to identify the genetic and environmental influences on the development of psychological traits. It is one of the oldest, most widely respected psychological studies in the world.

Principal investigators are David T. Lykken, Ph.D., Matt McGue, Ph.D., William Iacono, Ph.D., and Kevin Haroian, B.A. It involves several independent but related projects:

• Minnesota Twin Registry
• Minnesota Twin Study of Adult Development
• Minnesota Twin Family Study (Male Project)
• Minnesota Twin Family Study (Female Project)
• Sibling Interaction and Behavior Study

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Minnesota Twin Registry

The Minnesota Twin Registry was established in 1983. Its original goal was to establish a registry of all twins born in Minnesota from 1936 to 1955 to be used for psychological research. Recently, it has added twins born between 1961 and 1964. It primarily conducts personality and interests tests with its 8,000+ twin pairs and family members via mail. From this project, it was able to confirm that twins and their families are representative of the population and that a poll of their opinions would be more accurate than polls in the newspaper.

Minnesota Twin Family Study (MTFS)

MTFS was established in 1989 using same-gendered twin pairs age 11 or 17. All twins in born in MN at that time were invited to participate using birth registry data. 500 additional 11 year old twin-pairs were added in 2000. Twin studies are valuable to researchers because identical twins share 100% of their genes and fraternal twins share, on average, 50% of their genes. Both identical and fraternal twins share certain aspects of their environment (e.g. religious practices in the home). This allows researchers to estimate the heritability of certain traits. Participants are asked about academic ability, personality, and interests; family and social relationships; mental and physical health; physiological measurements. Of interest to researchers are prevalence of psychopathology, substance abuse, divorce, leadership, and other traits and behaviors related to mental and physical health, relationships, and religiosity.

The Minnesota Study of Twins Reared Apart

In 1979, Thomas Bouchard began to study twins who were separated at birth and raised in different families. He found that an identical twin reared away from his or her co-twin seems to have about an equal chance of being similar to the co-twin in terms of personality, interests, and attitudes as one who has been reared with his or her co-twin. This leads to the conclusion that the similarities between twins are due to genes, not environment, since the differences between twins reared apart must be due totally to the environment.

Sibling Interaction and Behavior Study

The Sibling Interaction and Behavior Study (SIBS) is a study of adoptive and biological siblings and their parents. Because adopted siblings are not biologically related to each other or their siblings, comparing families in which two siblings are both adopted, families in which one sibling is adopted and one is biologically related to the parents, and families in which both siblings are biologically related to the parents allows environmental and biological influence to be teased apart. It additionally allows sibling influence as well as parental influence to be studied. 617 families participated in the intake phase of this study. All families consisted of 2 parents and 2 teenage siblings. The primary purposes of this study are to understand how siblings interact and influence one another, how family environment has an impact on the psychological health of adolescents, and how adoptive families are similar to and different from nonadoptive families.

Criticism of Reared Apart Twin Research

• Farber, S. L. (1981). Identical twins reared apart: A reanalysis. New York: Basic Books.
• Joseph, J. (2004). The Gene Illusion: Genetic Research in Psychiatry and Psychology Under the Microscope.New York: Algora. (2003 United Kingdom Edition by PCCS Books)
• Joseph, J. (2001). Separated Twins and the Genetics of Personality Differences: A Critique. American Journal of Psychology, 114, 1-30
• Kamin, L. J. (1974). The Science and Politics of I.Q. Potomac, MD: Lawrence Erlbaum Associates.
• Taylor, H. F. (1980). The IQ Game: A Methodological Inquiry into the Heredity-Environment Controversy. New Brunswick, NJ: Rutgers University Press.

References

• Bouchard TJ Jr, Lykken DT, McGue M, Segal NL, Tellegen A (1990). "Sources of human psychological differences: the Minnesota Study of Twins Reared Apart". Science 250: 223–228. PMID 2218526.

• Iacono, W.G., & McGue, M. (2002). "Minnesota Twin Family Study". Twin Research, 5: 482–487.