Behavioral activation is a third generation behavior therapy for treating depression. It is one of many functional analytic psychotherapies which are based on a Skinnerian psychological model of behavior change, generally referred to as applied behavior analysis. This area is also a part of what is called clinical behavior analysis (CBA) (see behavior therapy) and makes up one of the most effective practices in the professional practice of behavior analysis.
Behavioral activation emerged from a component analysis of cognitive behavioral therapy. This analysis found that any cognitive component added little to the overall treatment of depression. The behavioral component had existed as a stand-alone treatment in the early work of Peter Lewinsohn and thus a group of behaviorists decided that it might be more efficient to pursue a purer behavioral treatment for the disorder. The theory holds that not enough environmental reinforcement or too much environmental punishment can contribute to depression. The goal of the intervention is to increase environmental reinforcement and reduce punishment.
The theoretical underpinnings of behavioral activation for depression is Charles Ferster's functional analysis of depression. Ferster's basic model has been strengthened by further development in the study of reinforcement principles which led to the matching law and continuing theoretical advances in the possible functions of depression, as well as a look at behavior analysis of child development in order to determine long-term patterns which may lead to dysthymia.
The behavioral activation (BA) approach to depression was as follows: participants were asked to create a hierarchy of reinforcing activities which were then rank-ordered by difficulty; participants tracked their own goals along with clinicians who used a token economy to reinforce success in moving through the hierarchy of activities; participants were measured before and after by the Beck Depression Inventory (BDI) and a great effect on their depression was found as a result of their treatment. This was then compared to a control group who did not receive the same treatment. The results of those who received behavioral activation treatment were markedly superior to those of the persons in the control group. Multiple clinics have since piloted  and developed the treatment 
A recent review of behavioral activation studies for depression found that it has a robust effect and that policy makers should consider it an effective treatment. A large-scale treatment study found behavioral activation to be more effective than cognitive therapy and on a par with medication for treating depression.
Other third generation behavior therapies
Behavioral activation comes under the heading clinical behavior analysis or what is often termed third generation behavior therapy. Other behavior therapies are acceptance and commitment therapy (ACT), as well as dialectical behavior therapy (DBT) and functional analytic psychotherapy (FAP). Behavioral activation owes its basis to Charles Ferster's Functional Analysis of Depression (1973) which developed B.F. Skinner's idea of depression, within his analysis of motivation, as a lack of reinforcement.
The Association for Behavior Analysis International has a special interest group for practitioner issues, behavioral counseling, and clinical behavior analysis. Association for behavior analysis international has larger special interest groups for behavioral medicine. Association for behavior analysis international serves as the core intellectual home for behavior analysts. The Association for Behavior Analysis International sponsors 2 conferences/year- one in the U.S. and one international.
The Association for Behavioral and Cognitive Therapies (ABCT) also has an interest group in behavior analysis, which focuses on clinical behavior analysis.
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