The purported association between depression, aggression, and self-injury in people with intellectual disability: a critical review of the literature.

The prevalence of depression in individuals with an intellectual disability is estimated to lie between 3% and 6%. It has been suggested that symptoms of depression in this population might be atypical and include unusual features such as challenging behavior. However, there is significant disagreement regarding the use of challenging behavior as "depressive equivalent" symptomatology. The aim of this review is to evaluate published research reporting on the association between challenging behavior, specifically aggression and self-injury, and depression in people with an intellectual disability as a first step toward evaluating whether challenging behaviors might be considered as depressive equivalent symptoms. The results of the studies identified indicated that the association between depression and aggression, and depression and self-injury are equivocal and the interpretations of the results limited by threats to validity. Based on this analysis, there is insufficient evidence to support the use of challenging behavior as a depressive equivalent symptom. Further research to examine potentially confounding variables and the association between challenging behaviour and depression using methodologically robust designs and measures is clearly warranted.