Older Brothers and Older Sisters Odds Ratios in 36 Samples of Homosexual Males
The fraternal birth order effect (FBOE) is the tendency for older brothers to increase the odds of homosexuality in later-born males. I recently investigated the reliability of this phenomenon in two non-overlapping meta-analyses. The first meta-analysis (Blanchard, 2018a) was carried out on 30 convenience samples from 26 studies, totaling 7140 homosexual and 12,837 heterosexual males. The second meta-analysis (Blanchard, 2018b) was carried out on 6 probability samples from 5 studies, totaling 2386 homosexual and 445,301 heterosexual males.
The FBOE was quantified the same way for each sample in both meta-analyses using a novel measure, the Older Brothers Odds Ratio (OBOR), which can be calculated both for published and for future studies and which automatically takes family size into account. The OBOR is computed as (homosexuals’ older brothers ÷ homosexuals’ other siblings) ÷ (heterosexuals’ older brothers ÷ heterosexuals’ other siblings), where other siblings = older...
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