Multidimensional assessment of sexual orientation and the fraternal birth order effect.

What is it about?

The study attempted to find the fraternal birth order effect (FBOE) using multiple methods and was unable to detect the effect in the study's current sample.

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Why is it important?

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.