Table 1.

Explanation of variance parameters in the 10 different simulated scenarios.

Parameter	Estimable in	Interpretation
VP, σ2	CTD, NTFD, Stealth, Cascade	Phenotypic variance.
VA	CTD*, NTFD**, Stealth, Cascade	Additive genetic variance; variance of marginal or average allelic effects.
VD	CTD*, NTFD**, Stealth, Cascade	Dominance genetic variance; variance of effects attributable to combinations of alleles at the same locus.
VC	CTD*, NTFD	VC = VS + VF; typically estimated in CTD models and some NTFD models. In the Stealth, Cascade, and some NTFD models, it is split into VS and VF.
VS	NTFD**, Stealth, Cascade	Sibling environmental variance; variance in non-genetic effects (e.g., peers, cohort, school, parenting style, etc) shared between siblings and twins but not between parents and offspring.
VF	NTFD**, Stealth, Cascade	Familial environmental variance; variance in non-genetic effects (e.g., SES, social mores, education) passed (via “vertical transmission”) from parents to offspring.
VT	NTFD, Stealth, Cascade	Twin environmental variance; variance in non-genetic effects (e.g., peers, cohort, classrooms, in utero effects) shared by twins but not siblings.
VE	CTD, NTFD, Stealth, Cascade	Unique or residual environmental variance; variance in non-genetic effects (e.g., peers, unique experiences, somatic mutations, measurement error) that are unshared with any other relative class.
VA×A	none	Additive-by-additive epistatic genetic variation; variance attributable to combinations of alleles’ additive effects at different loci
VA×Age	none	Non-scalar additive genetic-by-age interaction variance; this causes a reduction in additive genetic covariance between relatives as a function of their age difference.
CV(A, F)	NTFD, Stealth, Cascade	Covariance between additive genetic and familial environmental effects; arises if vertical transmission (causing VF) is a function of the parental phenotype because, e.g., higher values on A create higher phenotypic values, which are passed to offspring F via vertical transmission.

Note.

^*The CTD can estimate any two of V_A, V_D, or V_C.

^**The NTFD can estimate any three of V_A, V_D, V_S or V_F.