Abstract
The fraternal birth order (FBO) effect related to men’s sexual orientation refers to the finding that the number of older brothers that a man has increases his chance of being androphilic. The FBO effect has generally been well replicated in diverse samples; one instance of non-replication was by Francis (2008) using Waves I and III of the Add Health data. We attempted to replicate the FBO effect in the Add Health data taking into account family size and other limitations of Francis’ (2008) analyses. Also, we examined other sibling characteristics related to the FBO effect: sibling sex ratio and only-child status. We used two subsamples from Waves I (n = 20,745) and IV (n = 15,701) of the Add Health data, consisting of adolescents who were followed longitudinally from 1994 to 1995 until 2008. Wave I data were used to compute numbers of younger and older brothers and sisters from household roster information. Wave IV information about sexual orientation identity was used. Analyses were conducted within men and within women. We found modest support for the FBO effect in men, but not in women, using the older brother odds ratio, logistic regression analyses, and sibling sex ratio, which provided the strongest support for FBO. We found that gynephilic/biphilic women, but not androphilic/biphilic men, were more likely to be only-children compared to androphilic women and gynephilic men, respectively. We discuss limitations of the Add Health data and purported mechanisms for the FBO effect in men and the only-child effect in women.
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Notes
Also, at Wave IV a question was asked about total number of siblings: “How many brothers and sisters do you have, both living and deceased? Include biologically related, adoptive, and step-brothers or sisters.” We decided not to use this question because it provides no information about biological siblings, sex of the siblings, or age of the siblings. A household roster, similar to the Wave I household roster, was also completed at Wave IV. We decided not to use the Wave IV household roster given many individuals at that age (between 24 and 34 years of age) did not live with their siblings.
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Acknowledgements
This research uses data from Add Health, a program project directed by Kathleen Mullan Harris and designed by J. Richard Udry, Peter S. Bearman, and Kathleen Mullan Harris at the University of North Carolina at Chapel Hill, and funded by Grant P01-HD31921 from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, with cooperative funding from 23 other federal agencies and foundations. Special acknowledgment is due Ronald R. Rindfuss and Barbara Entwisle for assistance in the original design. Information on how to obtain the Add Health data files is available on the Add Health website (http://www.cpc.unc.edu/addhealth). No direct support was received from Grant P01-HD31921 for this analysis. Data acquisition was supported by a Social Sciences and Humanities Research Council Grant to A. F. Bogaert [335-737-042]. Thank you to R. Blanchard for help with analyses.
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Skorska, M.N., Bogaert, A.F. 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. Arch Sex Behav 49, 557–573 (2020). https://doi.org/10.1007/s10508-019-01496-x
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DOI: https://doi.org/10.1007/s10508-019-01496-x