Built and tested a large pool of items which measured both infant and adult attachment using factor-analysis.  They found five main factors which appeared to contribute to adult attachment. They then performed cluster analysis using these five factors as the clustering variables from which two main dimensions emerged: anxiety over relationships and discomfort with closeness. These dimensions later became labelled Anxiety (need for approval, preoccupation with relationships, fear of being abandoned) and Avoidance (discomfort with intimacy and closeness). They found that the five dimensions could be used to identify four attachment groupings which orresponded well with the four category system proposed by Bartholomew (1990).