The ubiquity of big brother

Teachers from grades K through 6 nominated the most physically active and most physically passive students from each sex. Half the schools were attended mainly by low-SES Mexican-American students and half upper-middle-SES Caucasian students. The main finding was that physically active students were more likely to have an older brother than were physically passive students. This effect was independent of sex, grade level, race, SES, and other-sibling combinations. A second study confirmed this relationship when college students rated themselves on the same active-passive dimension.