Fraternal Birth Order, Only-Child Status, and Sibling Sex Ratio Related to Sexual Orientation in the Add Health Data: A Re-analysis and Extended Findings

We examined birth order and sibling sex ratio in relation to sexual orientation within a Chinese cultural context. A total of 672 people comprising 160 heterosexual men, 215 homosexual men, 255 heterosexual women, and 42 homosexual women, took part in a web-based survey. Our results showed that as a whole homosexual and heterosexual men had a significantly late position in the birth order of the children in their families, but that the same phenomenon did not apply for homosexual women. In contrast to studies involving Western populations, in this study heterosexual and homosexual men had a significant excess of older sisters, but not older brothers when compared with the norm in a Chinese population. We concluded that the male-preference stopping rule adopted by Chinese parents affected birth order and sibling sex ratio in relation to sexual orientation.

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Birth Order, Sibling Sex Ratio, Handedness, and Sexual Orientation of Male and Female Participants in a BBC Internet Research Project

Archives of Sexual Behavior ◽

10.1007/s10508-006-9159-7 ◽

2007 ◽

Vol 36 (2) ◽

pp. 163-176 ◽

Cited By ~ 75

Author(s):

Ray Blanchard ◽

Richard A. Lippa

Keyword(s):

Sexual Orientation ◽

Sex Ratio ◽

Birth Order ◽

Internet Research ◽

Research Project ◽

Male And Female ◽

Sibling Sex Ratio

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

10.31234/osf.io/e4j6a ◽

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.

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