During the 1970's, psychologist Mary Ainsworth further expanded upon Bowlby's groundbreaking work in her now-famous "Strange Situation" study. The study involved observing children between the ages of 12 to 18 months responding to a situation in which they were briefly left alone and then reunited with their mother (Ainsworth, 1978).
Based on these observations, Ainsworth concluded that there were three major styles of attachment: secure attachment, ambivalent-insecure attachment, and avoidant-insecure attachment. Researchers Main and Solomon (1986) added a fourth attachment style known as disorganized-insecure attachment. Numerous studies have supported Ainsworth's conclusions and additional research has revealed that these early attachment styles can help predict behaviors later in life.
<http://psychology.about.com/od/loveandattraction/ss/attachmentstyle_2.htm>
