Applied behavior analysis (ABA) is the science of human behavior. Over the past 30 years, several thousand published research studies have documented the effectiveness of ABA across a wide range of:

• populations (children and adults with mental illness, developmental disabilities and learning disorders)
• interventionists (parents, teachers and staff)
• settings (schools, homes, institutions, group homes, hospitals and business offices), and
• behaviors (language; social, academic, leisure and functional life skills; aggression, self-injury, oppositional and stereotyped behaviors)

Applied behavior analysis is the process of systematically applying interventions based upon the principles of learning theory to improve socially significant behaviors to a meaningful degree, and to demonstrate that the interventions employed are responsible for the improvement in behavior (Baer, Wolf & Risley, 1968; Sulzer-Azaroff & Mayer, 1991).

"Socially significant behaviors" include reading, academics, social skills, communication, and adaptive living skills. Adaptive living skills include gross and fine motor skills, eating and food preparation, toileting, dressing, personal self-care, domestic skills, time and punctuality, money and value, home and community orientation, and work skills.

ABA methods are used to support persons with autism in at least six ways:

1. to increase behaviors (eg reinforcement procedures increase on-task behavior, or social interactions);
2. to teach new skills (eg, systematic instruction and reinforcement procedures teach functional life skills, communication skills, or social skills);
3. to maintain behaviors (eg, teaching self control and self-monitoring procedures to maintain and generalize job-related social skills);
4. to generalize or to transfer behavior from one situation or response to another (eg, from completing assignments in the resource room to performing as well in the mainstream classroom);
5. to restrict or narrow conditions under which interfering behaviors occur (eg, modifying the learning environment); and
6. to reduce interfering behaviors (eg, self injury or stereotypy).

ABA is an objective discipline. ABA focuses on the reliable measurement and objective evaluation of observable behavior.

Reliable measurement requires that behaviors are defined objectively. Vague terms such as anger, depression, aggression or tantrums are redefined in observable and quantifiable terms, so their frequency, duration or other measurable properties can be directly recorded (Sulzer-Azaroff & Mayer, 1991). For example, a goal to reduce a child's aggressive behavior might define "aggression" as: "attempts, episodes or occurrences (each separated by 10 seconds) of biting, scratching, pinching or pulling hair." "Initiating social interaction with peers" might be defined as: "looking at classmate and verbalizing an appropriate greeting."

ABA interventions require a demonstration of the events that are responsible for the occurrence, or non-occurrence, of behavior. ABA uses methods of analysis that yield convincing, reproducible, and conceptually sensible demonstrations of how to accomplish specific behavior changes (Baer & Risley, 1987). Moreover, these behaviors are evaluated within relevant settings such as schools, homes and the community. The use of single case experimental design to evaluate the effectiveness of individualized interventions is an essential component of programs based upon ABA methodologies. This is a process that includes the following components:

1. selection of interfering behavior or behavioral skill deficit
2. identification of goals and objectives
3. establishment of a method of measuring target behaviors
4. evaluation of the current levels of performance (baseline)
5. design and implementation of the interventions that teach new skills and/or reduce interfering behaviors
6. continuous measurement of target behaviors to determine the effectiveness of the intervention, and
7. ongoing evaluation of the effectiveness of the intervention, with modifications made as necessary to maintain and/or increase both the effectiveness and the efficiency of the intervention.

This process incorporates all of the features that constitute a favorable and accountable approach to behavior change (Sulzer-Azaroff & Mayer, 1991).