Attachment and Health
John Bowlby and Mary Ainsworth developed attachment theory in the 1960s while investigating the effects of maternal separation on infant development. The development of the Strange Situation task in 1965 by Ainsworth and Wittig allowed researchers to systematically investigate the attachment system operating between children and their parents. The Strange Situation involves separating infant-parent dyads and observing infant behaviours upon reunion. Infant behaviour tended to follow patterns, leading to the development of three attachment categories: Secure, Anxious-Avoidant, and Anxious-Resistant. In 1990, Ainsworth added a new category, championed by Mary Main, called Disorganized/Disoriented attachment, characterized by its less reliable pattern of behaviour.
Diathesis–stress model
The use of the term "diathesis" in medicine and in the specialty of psychiatry dates back to the 1800s; however, the diathesis–stress model was not introduced and used to describe the development of psychopathology until it was applied to explaining schizophrenia in the 1960s by Paul Meehl.
The diathesis–stress model is used in many fields of psychology, specifically for studying the development of psychopathology. It is useful for the purposes of understanding the interplay of nature and nurture in the susceptibility to psychological disorders throughout the lifespan. Diathesis–stress models can also assist in determining who will develop a disorder and who will not. For example, in the context of depression, the diathesis–stress model can help explain why Person A may become depressed while Person B does not, even when exposed to the same stressors. More recently, the diathesis–stress model has been used to explain why some individuals are more at risk for developing a disorder than others. For example, children who have a family history of depression are generally more vulnerable to developing a depressive disorder themselves. A child who has a family history of depression and who has been exposed to a particular stressor, such as exclusion or rejection by his or her peers, would be more likely to develop depression than a child with a family history of depression that has an otherwise positive social network of peers.