Abstract
Family survival data can be used to estimate the degree of genetic and environmental contributions to the age at onset of a disease or of a specific event in life. The data can be modeled with a correlated frailty model in which the frailty variable accounts for the degree of kinship within the family. The heritability (degree of heredity) of the age at a specific event in life (or the onset of a disease) is usually defined as the proportion of variance of the survival age that is associated with genetic effects. If the survival age is (interval) censored, heritability as usually defined cannot be estimated. Instead, it is defined as the proportion of variance of the frailty associated with genetic effects. In this paper we describe a correlated frailty model to estimate the heritability and the degree of environmental effects on the age at which individuals contact a social worker for the first time and to test whether there is a difference between the survival functions of this age for twins and non-twins.
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Acknowledgments
The project was financially supported by NDNS+. We thank Piet Groeneboom for using his computer program for computing the NPMLE for a survival curve based on interval censored survival data. We also thank Sandjai Bhulai for his help writing the computer program for maximizing the likelihood function. Last, but not least, we thank the twins and their family members for filling in the questionnaires.
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Open Access This is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License (https://creativecommons.org/licenses/by-nc/2.0), which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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Jonker, M.A., Boomsma, D.I. A frailty model for (interval) censored family survival data, applied to the age at onset of non-physical problems. Lifetime Data Anal 16, 299–315 (2010). https://doi.org/10.1007/s10985-009-9141-5
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DOI: https://doi.org/10.1007/s10985-009-9141-5