Behavior Genetics

, Volume 19, Issue 2, pp 209–222 | Cite as

Genetic and environmental contributions to the covariance between occupational status, educational attainment, and IQ: A study of twins

  • Kristian Tambs
  • Jon Martin Sundet
  • Per Magnus
  • Kåre Berg


Scores of occupational status, educational attainment, and IQ were obtained for 507 monozygotic and 575 dizygotic male twin pairs born 1931–1935 and 1944–1960. A multivariate genetic analysis with statistics from different cohorts showed heterogeneity between cohorts, and analyses were performed in four separate cohorts. The only set of results which departed clearly from the rest was found for the group born 1931–1935, where the ratio of environmental to genetic effects exceeded those of the other groups. Typical heritability values in the three youngest groups (weighted means) were .43, .51, and .66 for occupation, education, and IQ, respectively. The values in the oldest group were .16, .10, and .37, but this sample is small and the estimates are unstable. Genetic variance influencing educational attainment also contributed approximately onefourth of the genetic variance for occupational status and nearly half the genetic variance for IQ. The values for the between-families variances (reflecting family environment and assortative mating) varied from 2 to 35% in the three youngest groups but were higher for education (62%) and IQ (45%) in the oldest groups. All the between-families variance was common to all three variables. For educational attainment and IQ, the bulk of this between-families variance is probably genetic variance due to assortative mating. The common-factor environmental within-family variances were generally small, and the specific estimates seemed to contain mainly measurement error.

Key Words

intelligence educational attainment occupational status covariance analysis heritability twins 


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Copyright information

© Plenum Publishing Corporation 1989

Authors and Affiliations

  • Kristian Tambs
    • 1
  • Jon Martin Sundet
    • 2
  • Per Magnus
    • 3
  • Kåre Berg
    • 3
  1. 1.Department of Behavioural Sciences in MedicineUniversity of OsloOslo 3Norway
  2. 2.Institute of PsychologyUniversity of OsloOslo 3Norway
  3. 3.Institute of Medical GeneticsUniversity of OsloOslo 3Norway

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