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A Proposed Test of the Difference Between the Means of Monozygotic And Dizygotic Twins

Published online by Cambridge University Press:  27 January 2025

J.C. Christian  and
J.A. Norton Jr.
J.C. Christian*
Affiliation:
Departments of Medical Genetics and Psychiatry, Indiana University School of Medicine, Indianapolis, Indiana, USA
J.A. Norton Jr.
Affiliation:
Departments of Medical Genetics and Psychiatry, Indiana University School of Medicine, Indianapolis, Indiana, USA
*
Department of Medical Genetics, Indiana University School of Medicine, 1100 West Michigan Street, Indianapolis, Indiana 46202, USA

Abstract

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The rationale for using an approximate t′ test of the difference between the means of MZ and DZ twins is presented. This test avoids pooling the among-MZ and among-DZ twin-pair mean squares and has approximate degrees of freedom based upon the relative number of MZ and DZ twin pairs as well as the relative sizes of the among-MZ and among-DZ twin-pair mean squares. Sampling experiments simulating twin studies were used to show that the rate of Type I error for this t′ test was appropriate while other tests could give either too many or too few Type I errors depending upon the relative sizes of the mean squares and the relative numbers of MZ and DZ twin pairs.

Riassunto

RIASSUNTO

Viene illustrato un test t′ approssimato per la differenza fra medie di gemelli MZ e DZ. Il test evita di mettere insieme le medie quadratiche di gemelli MZ e DZ ed ha gradi di libertà approssimati basati sul numero relativo di coppie MZ e DZ, così come sul numero relativo delle medie quadratiche in gemelli MZ e DZ. Esperimenti di simulazione di studi gemellari sono stati usati per dimostrare che il tasso di errori di Tipo I per questo test t′ era appropriato, mentre altri test davano troppo pochi o troppi errori di Tipo I, in funzione della relativa entità delle medie quadratiche e del numero di coppie MZ e DZ.

Résumé

RÉSUMÉ

Un test t′ approximé pour la différence entre moyennes de jumeaux MZ et DZ est illustré. Ce test évite de mettre ensamble les moyennes des carrés de jumeaux MZ et DZ et a des degrés de liberté approximés, basés sur le nombre relatif de couples MZ et DZ ainsi que sur le nombre relatif des moyennes des carrés de jumeaux MZ et DZ. Des expériments de simulation d'études gémellaires ont été effectués afin de démontrer que le taux d'erreurs de Type I pour ce test t′ était approprié, alors que d'autres tests donnaient un nombre trop petit ou trop élevé d'erreurs de Type I, en fonction de la grandeur relative des moyennes des carrés et du nombre de couples MZ et DZ.

Zusammenfassung

ZUSAMMENFASSUNG

Beschreibung eines Tests, der die Differenz der Durchschnittswerte bei EZ und bei ZZ hervorbringen soll. Dieser Test t′ vermeidet die Verbindung der Quadratdurchschnittsziffern von EZ und ZZ und verfügt über annähernde Freiheitsgrade, die auf der relativen Zahl der EZ- und ZZ-Paare basieren, sowie auf der relativen Zahl der Quadratdurchschnittswerte bei EZ und ZZ. Es wurden simulierte Zwillingsexperimente angestellt, um zu beweisen, daβ die Fehlerrate des Typs I für diesen Test t′ angemessen war, während andere Tests, je nach der Höhe der Quadratdurchschnittswerte und der Zahl der EZ- und ZZ-Paare, zuviel oder zuwenig Fehler des Typs I ergaben.

Type
Research Article
Information
Acta geneticae medicae et gemellologiae: twin research , Volume 26 , Issue 1 , January 1977 , pp. 49 - 53
Copyright
Copyright © The International Society for Twin Studies 1977

References

REFERENCES

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