Researchers have concluded that an individual's happiness is largely a collective(集団の、共通の)affair, depending heavily on the happiness of one’s friends, one’s friends' friends, and even the friends of one’s friends' friends. These effects persist(尾を引く、存続する)across three degrees of separation; a happy third-degree friend increases a person's chance of being happy by 6%. Surprisingly, it appears that a next-door neighbor’s happiness has more impact on a person’s mood than a live-in partner.