Skip to main content

The Impact of Variation in Twin Relatedness on Estimates of Heritability and Environmental Influences


By taking advantage of the natural variation in genetic relatedness among identical (monozygotic: MZ) and fraternal (dizygotic: DZ) twins, twin studies are able to estimate genetic and environmental contributions to complex human behaviors. Recently concerns have been raised about the accuracy of twin studies in light of findings of genetic and epigenetic changes in twins. One of the concerns raised is that MZ twins are not 100% genetically and epigenetically similar because they show variations in their genomes and epigenomes leading to inaccurate estimates of heritability. This article presents findings from a simulation study that examined the degree of bias in estimates of heritability and environmentality when the genetic and epigenetic similarity of MZ twins differs from 1.00 and when the genetic and epigenetic similarity of DZ twins differs from 0.50. The findings suggest that in the standard biometric model when MZ or DZ twin similarity differs from 1.00 or 0.50, respectively, the variance that should be attributed to genetic influences is instead attributed to nonshared environmental influences, thus deflating the estimates of genetic influences and inflating the estimates of nonshared environmental influences. Although estimates of genetic and nonshared environmental influences from the standard biometric model were found to deviate from “true” values, the bias was usually smaller than 10% points indicating that the interpretations of findings from previous twin studies are mostly correct.

This is a preview of subscription content, access via your institution.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5


Download references

Author information

Authors and Affiliations


Corresponding author

Correspondence to Chang Liu.

Ethics declarations

Conflict of interest

Chang Liu, Peter C. M. Molenaar and Jenae M. Neiderhiser declare that they have no conflict of interest.

Human and Animal Rights and Informed Consent

This article does not contain any studies with human participants or animals performed by any of the authors.

Additional information

Edited by Pete Hatemi.

Electronic supplementary material

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Liu, C., Molenaar, P.C.M. & Neiderhiser, J.M. The Impact of Variation in Twin Relatedness on Estimates of Heritability and Environmental Influences. Behav Genet 48, 44–54 (2018).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:


  • Twin studies
  • Standard biometric model
  • Genetic and epigenetic similarity
  • Heritability estimate
  • Simulation study