Name	Definition	Method of estimation	Terminology
Phenotypic correlation	Correlation between two phenotypes in the same subject. In classical twin studies this is termed a within-twin cross-trait correlation	The ratio of the deviation from the population mean of the group mean in the secondary variable of the probands to the deviation from the population mean of the group mean in the primary variable of the probandsa	Bivariate group within-subject correlation
Shared familiality or cross-sibling cross-trait correlation	Correlation between siblings for two phenotypes. It is analogous to a dizygotic cross-twin cross-trait correlation in a twin study	The ratio of the deviation from the population mean of the group mean in the secondary variable of the siblings to the deviation from the population mean of the group mean in the primary variable in the probandsa	Bivariate sibling correlation
Percentage of phenotypic correlation due to shared familial effects		(2×bivariate familial correlation)/phenotypic correlation. This assumes that familial correlation is accounted for entirely by additive genesb

^aThe variances of the selection variable and the secondary variable have been equated.

^bThe percentage of phenotypic correlation due to additive genetic effects only holds in instances where the variance–covariance structure of the primary phenotype is known unequivocally.