8. Siblings & Parents
How your siblings and parents perceive you as well as how they treat you makes a big difference in your PBO.

9. Sexual Orientation?
Several studies have found that men with older brothers are more likely to be gay than those without and the more older brothers, the greater the likelihood.

10. Parents’ Birth Order
Parents tend to identify with kids who share their birth order. Which makes you wonder about the whole nature vs. nurture thing.