The Fraternal Birth Order Effect Is Robust and Important

2017 ◽  
Vol 47 (1) ◽  
pp. 17-19 ◽  
Author(s):  
J. Michael Bailey
Keyword(s):  
Birth Order ◽  
Order Effect ◽  
Birth Order Effect ◽  
Fraternal Birth Order ◽  
Fraternal Birth Order Effect

scholarly journals The Fraternal Birth-Order Effect as Statistical Artefact: Convergent Evidence from Probability Calculus, Simulated Data, and Multiverse Meta- Analysis

2021 ◽  
Author(s):  
Johannes K Vilsmeier ◽  
Michael Kossmeier ◽  
Martin Voracek ◽  
Ulrich S. Tran
Keyword(s):  
Sexual Orientation ◽  
Birth Order ◽  
Meta Analysis ◽  
Order Effect ◽  
Probability Calculus ◽  
Older Brothers ◽  
Birth Order Effect ◽  
Fraternal Birth Order ◽  
Fraternal Birth Order Effect ◽  
Ratio Variables

For a quarter of a century researchers investigating the origins of sexual orientation have largely ascribed to the fraternal birth order effect (FBOE) as a fact, holding that older brothers increase the odds of homosexual orientation among men through an immunoreactivity process. Here, we triangulate the empirical foundations of the FBOE from three distinct, informative perspectives: First, drawing on basic probability calculus, we deduce mathematically that the body of statistical evidence of the FBOE rests on the false assumptions that effects of family size should be controlled for and that this could be achieved through the use of ratio variables. Second, using a data-simulation approach, we demonstrate that by using ratio variables, researchers are bound to falsely declare corroborating evidence of an excess of older brothers at a rate of up to 100%, and that valid approaches attempting to quantify a potential excess of older brothers among homosexual men must control for the confounding effects of the number of older siblings. And third, we re-examine the empirical evidence of the FBOE by using a novel specification-curve and multiverse approach to meta-analysis. This yielded highly inconsistent and moreover similarly-sized effects across 64 male and 17 female samples (N = 2,778,998), compatible with an excess as well as with a lack of older brothers in both groups, thus, suggesting that almost no variation in the number of older brothers in men is attributable to sexual orientation.

THE CAUSE(S) OF THE FRATERNAL BIRTH ORDER EFFECT IN MALE HOMOSEXUALITY

2004 ◽  
Vol 36 (1) ◽  
pp. 51-59 ◽  
Author(s):  
WILLIAM H. JAMES
Keyword(s):  
Birth Order ◽  
Sexual Experience ◽  
Order Effect ◽  
Male Homosexuality ◽  
The Past ◽  
Older Brothers ◽  
Birth Order Effect ◽  
Fraternal Birth Order ◽  
Hormone Exposure ◽  
Fraternal Birth Order Effect

It has been established that the probability that a man is homosexual is positively related to his number of older brothers, but not older sisters when the brothers are accounted for. This is known as the ‘fraternal birth order’ effect. In the past, efforts have been made to explain this phenomenon in terms of several alternative biological hypotheses and a psychosocial hypothesis. This note examines how well these hypotheses accommodate the fraternal birth order effect. It is concluded that: (1) the evidence for the hypothesis of maternal immunoreactivity to the male fetus is weak; (2) the evidence for the intrauterine hormone exposure hypothesis is also weak; (3) the evidence for the hypothesis of postnatal learning is stronger. Lastly, there seem likely to be causes common to male homosexuality and paedophilia. They may include sexual (or quasi-sexual) experience in childhood or adolescence.

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