Reactive attachment disorder
The broad theoretical framework for current versions of RAD is attachment theory, based on work conducted from the 1940s to the 1980s by John Bowlby, Mary Ainsworth and René Spitz. Attachment theory is a framework that employs psychological, ethological and evolutionary concepts to explain social behaviors typical of young children. Attachment theory focuses on the tendency of infants or children to "seek proximity" to a "particular attachment figure" (familiar caregiver), in situations of alarm or distress, behavior which appears to have survival value. This is known as a discriminatory or selective attachment. Subsequently, the child begins to use the caregiver as a base of security from which to explore the environment, returning periodically to the familiar person. Attachment is not the same as love and/or affection although they are often associated. Attachment and attachment behaviors tend to develop between the ages of six months and three years. Infants become attached to adults who are sensitive and responsive in social interactions with the infant, and who remain as consistent caregivers for some time. Caregiver responses lead to the development of patterns of attachment, that in turn lead to internal working models which will guide the individual's feelings, thoughts, and expectations in later relationships. For a diagnosis of reactive attachment disorder, the child's history and atypical social behavior must suggest the absence of formation of a discriminatory or selective attachment.
Attachment measures
Scores on the anxiety and avoidance scales can still be used to classify people into the four adult attachment styles. 
The four styles of attachment defined in Bartholomew and Horowitz's model were based on thoughts about self and thoughts about partners. The anxiety scale in the ECR and ECR-R reflect thoughts about self. Attachment anxiety relates to beliefs about self-worth and whether or not one will be accepted or rejected by others. The avoidance scale in the ECR and ECR-R relates to thoughts about partners. Attachment avoidance relates to beliefs about taking risks in approaching or avoiding other people. Combinations of anxiety and avoidance can thus be used to define the four attachment styles. The secure style of attachment is characterized by low anxiety and low avoidance; the preoccupied style of attachment is characterized by high anxiety and low avoidance; the dismissive avoidant style of attachment is characterized by low anxiety and high avoidance; and the fearful avoidant style of attachment is characterized by high anxiety and high avoidance.