Simpson et al investigated the attachment theory through a longitudal study over 25 years with 78 participants. At 1 year, the parents reported on attachment behaviour. Between 6 and 8 years, teachers reported on peer relationships. At 16 they were asked about their close friendships and during adulthood, their romantic partners were asked to report on their experience. They found that those who were securely attached as infants had higher social competence in childhood, close friendships at 16 and more expressive and emotionally attached to romantic partners during adulthood.