Falconer's formula

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

The formula is hb2 = rmz - rdz, where hb2 is the broad sense heritability, rmz is the (monozygotic) identical twin correlation, and rdz is the (dizygotic) fraternal twin correlation.

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

hn2 = rsib - rad, where hn2 is the narrow sense heritability, rsib is the sibling correlation, and rad is the adoptee correlation.

Reference

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