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The Estimated Probability of Dizygotic Twins: A Comparison of Two Methods

Published online by Cambridge University Press:  21 February 2012

Jill Hardin ,
Steve Selvin ,
Suzan L. Carmichael  and
Gary M. Shaw
Jill Hardin*
Affiliation:
March of Dimes, California Research Division, Children's Hospital Oakland Research Institute, Oakland, California, United States of America; University of California, Berkeley, School of Public Health, Berkeley, California, United States of America. [email protected]
Steve Selvin
Affiliation:
University of California, Berkeley, School of Public Health, Berkeley, California, United States of America.
Suzan L. Carmichael
Affiliation:
March of Dimes, California Research Division, Children's Hospital Oakland Research Institute, Oakland, California, United States of America.
Gary M. Shaw
Affiliation:
March of Dimes, California Research Division, Children's Hospital Oakland Research Institute, Oakland, California, United States of America; University of California, Berkeley, School of Public Health, Berkeley, California, United States of America.
*
*Address for correspondence: Jill Hardin, March of Dimes, California Research Division, Children's Hospital Oakland Research Institute, 5700 Martin Luther King Jr Way, Oakland, CA 94609, USA.

Abstract

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This study presents a general model of two binary variables and applies it to twin sex pairing data from 21 twin data sources to estimate the frequency of dizygotic twins. The purpose of this study is to clarify the relationship between maximum likelihood and Weinberg's differential rule zygosity estimation methods. We explore the accuracy of these zygosity estimation measures in relation to twin ascertainment methods and the probability of a male. Twin sex pairing data from 21 twin data sources representing 15 countries was collected for use in this study. Maximum likelihood estimation of the probability of dizygotic twins is applied to describe the variation in the frequency of dizygotic twin births. The differences between maximum likelihood and Weinberg's differential rule zygosity estimation methods are presented as a function of twin data ascertainment method and the probability of a male. Maximum likelihood estimation of the probability of dizygotic twins ranges from 0.083 (95% approximate CI: 0.082, 0.085) to 0.750 (95% approximate CI: 0.749, 0.752) for voluntary ascertainment data sources and from 0.374 (95% approximate CI: 0.373, 0.375) to 0.987 (95% approximate CI: 0.959, 1.016) for active ascertainment data sources. In 17 of the 21 twin data sources differences of 0.01 or less occur between maximum likelihood and Weinberg zygosity estimation methods. The Weinberg and maximum likelihood estimates are negligibly different in most applications. Using the above general maximum likelihood estimate, the probability of a dizygotic twin is subject to substantial variation that is largely a function of twin data ascertainment method.

Keywords

zygosity estimation methodologyprobability of a malemaximum likelihood estimationWeinberg's differential rule
Type
Articles
Information
Twin Research and Human Genetics , Volume 12 , Issue 1 , 01 February 2009 , pp. 79 - 85
Copyright
Copyright © Cambridge University Press 2009