DeFries–Fulker regression

Approach

DeFries–Fulker regression analysis is based on the differences in the magnitude of regression to the mean in a genetic trait between monozygotic (MZ) and dizygotic (DZ) twins. In DF regression, the first step is to select probands in a twin study with extreme scores on the trait being studied, and to regression to the mean among their co-twins depending on whether the probands are part of a MZ or DZ twin pair. DF regression is thus based on the assumption that, to the extent that genetic factors play a role in causing the extreme variation in the studied trait, the magnitude of regression to the mean should be greater in DZ co-twins of probands than in their MZ counterparts. This should result in MZ co-twins being more similar to their probands on the trait under study than DZ twins are to theirs.

Modifications

Since the DF regression approach was first proposed in 1985, other researchers have proposed modified versions of the DF model that take additional factors into account, including observed covariates and opposite-sex DZ twins.