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Heteropaternal superfecundation (HP) occurs when two or more ova are fertilized by sperm from separate males. The resulting siblings are genetically equivalent to half-siblings and share, on average, 25% of their inherited genetic material. In the absence of genetic testing HP siblings could be treated as dizygotic (DZ) twins in behavioral genetic analyses and bias heritability estimates in phenotypic decomposition models. However, the extent to which such misclassification could affect calculated estimates of heritability is currently unknown. Employing simulation analyses, the current study assessed the potential biasing impact across a variety of conditions varying by proportions of DZ twins, sample sizes, and low, moderate, and high levels of genetic and environmental contribution to phenotypic variance. Overall, the results indicated that misclassified HP siblings had minimal impact on estimates of heritability. Nonetheless, greater attention should be paid to the identification of HP siblings within existing and future twin datasets.

The present study examined the adequacy of a three-item parent questionnaire in determining the zygosity of young Chinese twins and whether there was any association between parent response accuracy and some demographic variables. The sample consisted of 334 pairs of same-sex Chinese twins aged from 3 to 11 years. Three scoring methods, namely the summed score, logistic regression, and decision tree, were employed to evaluate parent response accuracy of twin zygosity based on single nucleotide polymorphism (SNP) information. The results showed that all three methods achieved high level of accuracy ranging from 91 to 93 % which was comparable to the accuracy rates in previous Chinese twin studies. Correlation results also showed that the higher the parents' education level or the family income was, the more likely parents were able to tell correctly that their twins are identical or fraternal. The present findings confirmed the validity of using a three-item parent questionnaire to determine twin zygosity in a Chinese school-aged twin sample.