Multidimensional assessment of sexual orientation and the Fraternal Birth Order Effect

Previous research demonstrates that for every older male sibling a male child has, the odds are increased by 33% over the naturally occurring odds that he will be nonheterosexual. This concept is known as the Fraternal Birth Order Effect (FBOE). Although this finding has been duplicated in multiple studies, researchers have not used other dimensions of sexual orientation when measuring the presence of the FBOE. The present study measures the FBOE in a racially diverse sample of right-handed men using a multidimensional assessment of sexual orientation that measures self-identified sexual orientation, sexual behaviors, sexual attractions, and sexual fantasies. The current study did not find the presence of the FBOE using Slater's Index, Berglin's Index, or Blanchard's Proportion in right-handed men regardless of being grouped by self-identified sexual orientation, sexual behaviors, sexual attractions, or sexual fantasies. Reasons for not observing a FBOE in the current data set are discussed and implications for future research are proposed.