Functional analysis in behavioral psychology is the application of the laws of operant and respondent conditioning to establish the relationships between stimuli and responses. To establish the function of operant behavior, one typically examines the "four-term contingency": first by identifying the motivating operations (EO or AO), then identifying the antecedent or trigger of the behavior, identifying the behavior itself as it has been operationalized, and identifying the consequence of the behavior which continues to maintain it.
Functional assessment in behavior analysis employs principles derived from the natural science of behavior analysis to determine the "reason", purpose, or motivation for a behavior. The most robust form of functional assessment is functional analysis, which involves the direct manipulation, using some experimental design (e.g., a multielement design or a reversal design) of various antecedent and consequent events and measurement of their effects on the behavior of interest; this is the only method of functional assessment that allows for demonstration of clear cause of behavior.
Functional analysis and consequence analysis are commonly used in certain types of psychotherapy to better understand, and in some cases change, behavior. It is particularly common in behavioral therapies such as behavioral activation, although it is also part of Aaron Beck's cognitive therapy. In addition, functional analysis modified into a behavior chain analysis is often used in dialectical behavior therapy.
There are several advantages to using functional analysis over traditional assessment methods. Firstly, behavioral observation is more reliable than traditional self-report methods. This is because observing the individual from an objective stand point in their regular environment allows the observer to observe both the antecedent and the consequence of the problem behavior. Secondly, functional analysis is advantageous as it allows for the development of behavioral interventions, either antecedent control or consequence control, specifically designed to reduce a problem behavior.