Falconer's formula

Falconer's formula is used in twin studies to determine the genetic heritability of a trait based on the difference between twin correlations.

The formula is H_b² = 2(r_mz - r_dz), where H_b² is the broad sense heritability, r_mz is the (monozygotic, MZ) identical twin correlation, and r_dz is the (dizygotic, DZ) fraternal twin correlation. The correlation of same sex MZ twins is always higher than the DZ twin correlation with various sexes and thus all gender differences are evaluated as heritable. To avoid this error, only genetic studies comparing MZ twins with the same sex DZ twins are valid. Or correlation between A = h_b² (additive genetics) and C (common environment) must be included in derivation

r_mz = A + C + 2 Corr(A,C)

r_dz = ½A + C + 2 Corr(½A,C)

and can not be neglected (also as covariance in the statistical model).

It is also possible to do narrow-sense heritability estimates by using sibling/adoptee correlations:

h_n² = r_sib - r_ad, where h_n² is the narrow sense heritability, r_sib is the sibling correlation, and r_ad is the adoptee correlation.

References

• Falconer, DS, MacKay TFC. Introduction to Quantitative Genetics, 4th Ed. 1996. Longmans Green, Harlow, Essex, UK.

See also

• Douglas Scott Falconer
• Quantitative genetics