Applied behavior analysis (ABA) is a way to help organisms change their behavior, and to identify the environmental contingencies that result in this behavior change. ABA, the application of behavior analysis, is based on the scientific approach known as radical behaviorism, which views covert events as behavior that are to be subjected to the same conditions as overt behavior. ABA can be used as a treatment for animals, mental disorders, and developmental disabilities, and is based on the principles of behavior that were discovered using experiments.

History
Scientific experiments and articles about ABA are published in the Journal for Applied Behavior Analysis (JABA.) This journal was founded in 1968. In the first issue of JABA, three people wrote an article explaining what Applied behavior analysis is.

Psychologists who study the way the environment influences behavior are called behaviorists. They study the external causes of behavior instead of a person's feelings. A person's feelings are internal so behaviorists think they cannot be studied scientifically.

Psychologist John B. Watson founded Behaviorism in 1913 and he is regarded as one of the first psychologists to study the applied science of behavior. He thought that internal feelings should not be studied at all. He also thought that behavior is shaped by the environment over time due to the outcome of a person's actions. He believed all behavior is learned and can be changed. If a person gets something good as a result of doing a behavior they are more likely to repeat that behavior. If something bad happens as a result of a behavior a person is less likely to do that thing again. This is an idea that is used a lot in ABA.

One of the most famous behaviorists was the psychologist B.F. Skinner. Skinner first published his ideas about behaviorism in 1938. He wrote a lot about behaviorism throughout his career. He made some of the behavior principles that ABA uses.

ABA emerged when experimental behavior principles were applied to social behavior. There are various people that began the process of applying these principles to social behavior. One of the most famous was Ole Ivar Lovaas. In the 1960s, Lovaas became one of the first people to use applied behavior analysis as a treatment for autism. When Lovaas began using ABA to treat children with autism he changed the way developmental disorders were treated. Lovaas also thought that treatments would be more successful if they are started early in a child's life. The idea of starting treatment with a child as soon as possible is called 'early intervention'. Early intervention is still thought to be very important in ABA.

One of the more recent developments in Applied Behavior Analysis is the founding of the Behavior Analysis Certification Board (BACB). The BACB is a non-profit corporation that was started in 1998. The BACB certifies behavior analysts. In order to become a behavior analyst a person must go to a special school and then pass an exam. Once they pass this exam they will be  board certified behavior analysts. The BACB sets standards to make sure board certified behavior analysts (BCBAs) are good at their jobs. The BACB makes sure that the BCBAs are using ethical, legal, and professional practices when they work.

Characteristics 
There are seven characteristics of ABA  A treatment that is based on ABA must have all of these things.

 Applied: This means that the behavior being studied must be socially important. Socially important behavior is behavior that happens in everyday life.   
 Behavioral: A behavior is anything that a person does. Feelings are not studied because they are internal so they cannot be measured. ABA treatments measure rates of behavior. 
 Analytic: For behavior to be analytic a behavior analyst has to have control over it. This means they have to be able to make the behavior happen at certain times. The data from before the experimental variable is applied is called baseline data. 
 Technological: The word technological is used to describe the amount of explanation necessary for a treatment. A behavioral intervention must be explained very well. If an intervention is not explained well it is not technological. 
 Conceptually systematic: For an ABA treatment to be conceptually systematic it must be related to behavior principles that are already known. Using principles that are already known makes ABA more effective. 
 Effective: This means that behavioral interventions must produce good results to be used in ABA. The purpose of applied interventions is to improve an aspect of social behavior. 
 Generality: This is used to show how meaningful a behavior change is. A behavior change has high generality if:
 The change keeps happening for a long time after the intervention is over
 The change happens in different environments
 The change causes a change in other behaviors

Definitions and concepts 
The following terms and ideas are used in Applied Behavior Analysis. It is important to understand these ideas when using ABA based interventions.

Problem behavior 
In ABA, a behavior that is bad is called a problem behavior. Problem behavior is something that hurts the person doing it or hurts other people around them. A problem behavior makes it harder for a person to learn new things.

 Operant behavior is the opposite of respondent behavior. Operant behavior is voluntary and can be changed. A person has control over their own operant behavior. They decide which behaviors they want to do. Respondent behavior cannot be controlled like operant behavior. ABA studies operant behavior more than respondent because it can be controlled. If a behavior can be controlled then it can be changed.
 Three-term contingency is a concept for understanding operant behavior that was first used by B.F. Skinner. It is still used in ABA. The three-term contingency says that every behavior has an antecedent and a consequence. An antecedent is what happens right before the behavior. The antecedent can change the chance that a behavior will happen. Some antecedents make a behavior more likely to happen. Other antecedents make a behavior less likely to happen. The consequence is what happens after the behavior. It is the response to the behavior. ABC data can be used to find things that may be causing behavior. Then these causes can be tested using experimental variables.
 An operational definition tells people exactly what a target behavior looks like. The target behavior is the behavior that is trying to be changed. The operational definition of the target behavior needs to be very good. People that have not seen the target behavior before should be able to tell when it happens based only on the operational definition. A good operational definition makes the study of behavior better.
 Reinforcement: When something increases the likelihood of a response happening again it is called a reinforcement. A reinforcement is often thought of as a reward. A reward is anything that is given after a response happens. A reward can only be a reinforcement if it increases the rate of response in the future. If it does not increase the rate of response then it is not a reinforcement. All reinforcers do not work for all people. So it is important to try different types of reinforcers to find out what works best for a person.

Primary reinforcers are reinforcers that fill a biological need. The four primary reinforcers are food, water, warmth and sex. Reinforcers that do not fill biological needs are called secondary reinforcers. Secondary reinforcers are not naturally reinforcing. A person needs to learn that they are reinforcing. They learn that they are reinforcing because they are paired with other things that are known to be reinforcing. They are also called conditioned reinforcers.

A discriminative stimulus (SD) is something that tells a person that reinforcement is available. The presentation of a SD should cause a response.

Positive reinforcement  
Positive reinforcement (SR+) is when the addition of a stimulus leads to an increase in responding. There are four different types of positive reinforcement:

 Tangible reinforcers are things that can be held. Toys or food would be tangible reinforcers. Tangible reinforcers can be expensive. They should not be the first choice for positive reinforcement.
 Social reinforcement is one of the best types of positive reinforcement. It is good because it is not expensive. It is also easy to use. Social reinforcers are things that have social value or meaning. Examples of social reinforcers would be awards, praise, or compliments. Social reinforcement can be very effective.
 Activity reinforcers are any events that a person can earn. Examples of some activities would be getting to play games, go to the movies, or earning a break. Activity reinforcers can work really well if the person really wants to earn the activity. But activity reinforcers may not be able to be earned right after the behavior happens. This would result in a delay of reinforcement. The reinforcer will be less effective if it is given a long time after the behavior happens.
 Token reinforcers are any neutral stimulus that can be traded for an object or activity. The objects or activities they can trade tokens for are known as back-up reinforcers. The tokens do not have value by themselves. They are only valuable because the person knows that they can trade them for something they want to earn.

Negative reinforcement 
Negative reinforcement (SR-) happens when the removal of a stimulus increases the likelihood a person will do a behavior in the future. In this case the term negative does not mean bad. The stimulus that is removed from the environment is something aversive. This means that the person does not like it. People will want to do a behavior if they know that something they do not like will be taken away.

Reinforcement schedules 
Reinforcements are given based on schedules of reinforcement. The schedule will explain the ways reinforcement is earned. Behavior analysts decide which reinforcement schedule is best. Different schedules are useful for different things. The schedule used depends on the person. It also depends on the behavior that is being reinforced.

Continuous reinforcement schedules 
Continuous reinforcement schedules (CRF) reinforce a person every time they do the target behavior. There are a few problems with CRF schedules though. The rates of behavior are not long-lasting. If the person stops being reinforced they may stop doing the target behavior. Another issue is satiation. If the person becomes satiated it means that they do not want the reinforcer anymore.

Intermittent reinforcement schedules 
These schedules of reinforcement only reinforce the target behavior sometimes. The four most common types of intermittent schedules are:

 Fixed-ratio schedules (FR) give reinforcement after a certain number of responses.
 Variable-ratio schedules: With variable-ratio (VR) schedules the amount of responses needed for reinforcement changes. The number of responses needed for reinforcement will be different every time.
 Fixed-interval schedules:  With fixed-interval (FI) schedules reinforcement is delivered for the first response that happens after a fixed amount of time passes.
 Variable-interval schedules (VI) give reinforcement after an variable amount of time passes.

Differential reinforcement 
A discriminative stimulus (SD) is something that tells a person that reinforcement is available. The presentation of a SD should cause a response. Differential reinforcement teaches a person the difference between a SD and a non-discriminative stimulus (S-delta). A SD signals that reinforcement is available. A S-delta does not tell the person anything about the availability of reinforcement. A S-delta is not likely to produce responses because there is reinforcement is not given.

It is also used to decrease problem behavior. There are four types of differential reinforcement that can be used to decrease a problem behavior.

DRL stands for differential reinforcement of a "low-rate" of response. DRL is helpful when trying to decrease a behavior but not get rid of it completely.
DRO stands for differential reinforcement of "other" behavior. With DRO, a person gets a reinforcer if they do not do the problem behavior for a set amount of time.
DRI stands for differential reinforcement of "incompatible" behavior. A DRI program reinforces behavior that is incompatible with the problem behavior. An incompatible behavior would stop them from being able to do the problem behavior.
DRA stands for differential reinforcement of "alternative" behavior. For a DRA program the person is taught an alternative behavior that they can do instead of the problem behavior.

Extinction 
Extinction is a way to decrease rates of problem behavior. A DRA program should be used at the same time as an extinction program. This will make the extinction program more effective.

Punishment 
Reinforcement is always the first thing that is tried when trying to change a behavior. Reinforcement produces long-lasting results and is better for the person. However reinforcement does not always reduce problem behavior. If reinforcement does not work it may be necessary to try punishment. Punishment is effective but it can have bad consequences. It can cause emotional harm if it is not used correctly.

Punishment is any response to a behavior that "decreases" the likelihood of a behavior happening in the future. Punishment of a problem behavior should be used with reinforcement of the appropriate behavior. Appropriate behavior should always be reinforced even when using punishment for problem behavior. Just like reinforcement, punishment can be both positive and negative. Positive punishment is the addition of an stimulus that decreases the chances of future responses. This stimulus that is added is something aversive. Negative punishment is the removal of a stimulus that decreases the chance of future behaviors happening. The stimulus that is removed is something that the person likes.

Prompting 
Prompting increases the likelihood that a behavior will be done the right way. Using prompts will make the learning process easier and quicker. Someone that is teaching a new behavior can use prompts to help the person that is learning the behavior. The two broad categories of prompts are stimulus and response.

Examples of stimulus prompts would be: lists or pictures that help the learner remember what the correct response is.

Response prompts do not involve a change in the antecedent. There are three types of response prompts.

The first type is verbal prompts.  
The second type of response prompt is a gestural prompt. The most common gestural prompt is pointing to the correct response. 
The third type of response prompt is a physical prompt. A physical prompt is when the teacher touches the learner in order to help them perform the correct behavior. Physical prompts are often used when teaching new skills that involve movement of the body.

Fading 
Fading prompts is a way to increase the independence of the learner. Once the learner can do the behavior on their own they will not need the help of the teacher. However, if a teacher stops using prompts quickly it may confuse the learner. So prompts should be decreased slowly. The process of gradually decreasing prompting is called 'fading'.

Shaping 
Shaping is a way to teach new behaviors or improve behaviors that have already been taught. It involves reinforcing steps towards a target behavior.

Chaining  
Complex behaviors are made up of smaller simple behaviors. This is what the concept of behavior chains is based on. A behavior chain is when smaller behaviors are combined to form a complex behavior. These smaller behaviors are done in a certain order. Each of the smaller behaviors is a step in the behavior chain. Each step in a behavior chain is a response on its own. There are three different ways to teach a behavior chain:

Forward chaining is the most common way to teach a behavior chain. The chain is taught starting with the first step. Once the learners can do the first step they move on to the second step. This continues until they have completed all of the steps. 
Backward chaining is the opposite of forward chaining. With backward chaining the last step is taught to the learners first. Once they can do the last step they move on to the second to last step. This continues until they make it to the first step. 
Total task presentation is the third way to teach a behavior chain. With forward and backward chaining only one step in the behavior chain is taught at one time. But with total task the learner completes every step in the chain every time they do the program. They should complete every step in the correct order. Total task requires the learner know how to do all of the steps in the chain before they start the program.

Analyzing behavior 
ABA relies on data to make decisions about behavior. Behavior analysts are always collecting data about a person's behavior.

Data collection 
Direct observation is when behavior is watched and recorded. Indirect measures compare one person's behavior to other people's behavior. An example would be an intelligence test. One person's score is compared to the scores that other people got.

There are three common methods of data collection. They are frequency, interval, and time sampling. These methods are used for direct observation.

Frequency is how often a behavior happens. So frequency recording just counts the number of times a behavior happens.
Interval recording breaks the observation time into smaller pieces. The total time is divided into smaller intervals. If the behavior happens at any time during one of the smaller intervals it is recorded.
Time sampling methods are a little different from frequency and interval methods. The observer will only look to see if the behavior is happening every once in a while. If the behavior is happening when the observers looks it gets recorded. But if the behavior happens any other time it does not get recorded. So the behavior is only recorded sometimes.

Functional analysis 
A functional analysis (FA) is done to find the reason for problem behavior. The reason for problem behavior must be known before a behavioral intervention can be done. Behavior analysts came up with the idea of a functional analysis in 1982. Since then it has become an important part of ABA. The behavior analyst is tries to find the situations that cause the highest rates of problem behavior. The situations that cause the highest rates of problem behavior tell the behavior analyst the reason for the behavior. Once the reasons for problem behavior are known treatment can begin.

Treatments based on the results of a FA are more effective than without a FA.

Use for treatment of autism  
Applied behavior analysis is commonly associated with autism. This is because ABA is the only treatment for autism that has been scientifically proven to be effective.

References  

Human behavior
Psychology