Am J Psychiatry 1996; 153:27-31
Copyright © 1996 by American Psychiatric Association
Homosexuality in men and number of older brothers
R Blanchard and AF Bogaert
Clarke Institute of Psychiatry, Toronto, Ontario, Canada.
OBJECTIVE: This study investigated whether homosexual men have a higher
mean birth order than heterosexual men primarily because they have more
older brothers or because they have more older siblings of both sexes.
METHOD: For the main analyses, 302 heterosexual men were individually
matched on year of birth with an equal number of heterosexual men. Each
completed a self-administered, anonymous questionnaire concerning family
background and other biodemographic information. RESULTS: Logistic
regression analysis showed that homosexuality was positively correlated
with the proband's number of older brothers but not with older sisters,
younger brothers, younger sisters, or parental age at the time of the
proband's birth. Each additional older brother increased the odds of
homosexuality by 33%. CONCLUSIONS: These results restrict the range of
possible theories of the birth order phenomenon to those that can explain
not only why older brothers increase the probability of homosexuality in
later-born males but also why older sisters neither enhance this effect nor
counteract it.
