Sampling Variances in Twin and Sibling Studies of Man

Abstract

The sampling variances in twin and sibling studies of man for estimation of intraclass correlation coefficients and their relation to heritabilities are evaluated. For twins and full-sibs the higher the estimated heritability of a trait the smaller the sampling variance. With increase in the number of twin sets or of full-sibships studied, the sampling variances decrease by their proportions. Twin and full-sib studies with lower heritabilities (h² < 0.25) need at least 50 sibships to obtain a significant estimate. Using half-sibs to estimate heritabilities, increase of the offspring number from the same parent would be more efficient for reducing the sampling variance of the heritability compared with increases of half-sibship families. However, because of the limited number of offspring per family in modern man, the efficiency of the half-sib design could be increased by the large number of monozygotic twin families. It appears that with only 2 or 3 children per full-sibship family, approximately 100 half-sibships are needed for significant estimate of heritability.

Twin Half-sibs: A Research Design for Genetic Epidemiology of Common Dental Disorders

“…Such data are basic to genetic studies of caries and periodontal status and should be obtained along with phenotype and risk-factor data, and their effects should be treated as covariates. Kang et al (1974) investigated the efficiency of the twin half-sib design relative to sample size. These workers concluded that the variance of estimates of the genetic half-sib intra-class correlation coefficient stabilized with 100 half-sibships.…”

The value of twins in dental research

“…They are also likely to be more similar in age than half-siblings in families formed following the death of a spouse or divorce. Despite its advantages, including efficiency in relation to sample size, 24 Potter's 23 encouragement to researchers to use the half-sib model to study common dental diseases has so far gone unheeded. However, Harrap and colleagues have used the model productively in a study of cardiovascular risk factors in Australians.…”

Genetic Studies of the Offspring of Identical Twins - A Model for the Analysis of Quantitative Inheritance in Man

“…A model for the analysis of data from MZ twin " half-sibships " is developed here and its usefulness is explored. For previous descriptions and applications of the model see Bader et al (1973), Bingle (1974) Kang et al (1974), Nance et al (1974), and Nance (1975).…”