Table 2.

Robustness of the retrospective likelihood methods to violation of the probit model assumption for the primary phenotype: estimates of the effect size of the single‐nucleotide polymorphism on the secondary phenotype (β ₁) and heritability of the secondary phenotype are given for a common disease (prevalence ≈5%), for the two ascertainment mechanisms and two values of α ₁.

Ascertainment	α 1	β 1	Heritability
0. True value		0.200	0.500
1. At least two cases
	0.100	0.199 (0.104) (0.104) (0.948)	0.509 (0.017) (0.110)
	0.500	0.197 (0.106) (0.110) (0.945)	0.516 (0.014) (0.108)
2. At least one case
	0.100	0.200 (0.104) (0.107) (0.961)	0.510 (0.012) (0.096)
	0.500	0.199 (0.107) (0.111) (0.960)	0.513 (0.010) (0.087)

In brackets are standard deviations, root mean square error and coverage probability (for the effect size only). Datasets consist of 400 sibships of size 5. Results are based on 500 replicates.