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The Estimation of Probandwise Concordance in Twins: The Effect of Unequal Ascertainment

Published online by Cambridge University Press:  01 August 2014

K.S. Kendler  and
L.J. Eaves
K.S. Kendler*
Affiliation:
Departments of Psychiatry, Virginia Commonwealth University/Medical College of Virginia, Richmond, USA Department of Human Genetics, Virginia Commonwealth University/Medical College of Virginia, Richmond, USA
L.J. Eaves
Affiliation:
Department of Human Genetics, Virginia Commonwealth University/Medical College of Virginia, Richmond, USA
*
Box 710 MCV Station, Richmond, VA 23298-0710, USA

Abstract

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This report examines the impact of two major kinds of unequal ascertainment on the estimation of true probandwise concordance (Cpbt ) in twin studies: 1) concordance-dependent – where the ascertainment rate differs in affected members of concordant vs discordant pairs, and 2) non-independent – where ascertainment rates differ in affected members of concordant pairs where the cotwin has vs has not been ascertained. Concordance-dependent ascertainment is easily modeled algebraically; non-independent ascertainment is more complex and we here propose a model based on survival analysis. Overall, concordance-dependent ascertainment produces greater bias in estimates of probandwise concordance than does non-independent ascertainment. The bias introduced by concordance-dependent ascertainment is greatest when Cpbt is low and/or when the ascertainment rate for twins in concordant pairs is low. The bias introduced by non-independent ascertainment is greatest when Cpbt is high and/or when the ascertainment probability for an affected twin in a concordant pair where the cotwin has already been ascertained approaches unity. The impact of concordance-dependent and non-independent ascertainment on estimates of heritability and common environment is examined. Correction terms to estimate Cpbt in the presence of concordance-dependent and/or non-independent ascertainment are presented.

Keywords

ConcordanceAscertainmentSurvival analysisTwins
Type
Research Article
Information
Acta geneticae medicae et gemellologiae: twin research , Volume 38 , Issue 3-4 , October 1989 , pp. 253 - 270
Copyright
Copyright © The International Society for Twin Studies 1989

References

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