— A key participant’s chances of becoming obese increased by 57 percent if he or she had a close friend who became obese.
— In same-sex friendships, a close friend becoming obese increased a key participant’s chance of becoming obese by 71 percent. However, no such association was found in opposite-sex friendships.
— The perception of friendship also was an important factor. When two people identified each other as close friends, the key participant’s risk of becoming obese increased by 171 percent if his or her friend became obese. In contrast, a key participant was not likely to become obese if someone claimed a close friendship with him or her but the key participant did not report the friendship.
— Among pairs of siblings, one’s becoming obese increased the other’s chance of becoming obese by 40 percent. This finding was more marked among same-sex siblings than opposite-sex siblings.
— In married couples, one spouse’s becoming obese increased the likelihood of the other spouse becoming obese by 37 percent. Husbands and wives appeared to affect each other equally.
— Obesity spread across social ties, despite geographic distance from one person to another.
— Further, social distance the degree of social separation between two people in the network, appeared to make more of a difference than geographic distance in the spread of behaviors and norms associated with obesity.
— An immediate neighbor’s becoming obese did not affect a person’s risk of becoming obese.
— Smoking behavior was not associated with the spread of obesity from person to person.
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