What is ABA and ABAB Design in Applied Behavior Analysis?

Psychology has been criticized for many years as an inexact science.  Critics say its weakness is that it doesn’t rely on empirical data. The introduction of different types of ABA research designs have done much to dispel that idea. The ABA and ABAB design are especially useful in applied behavioral analysis (ABA) as they help therapists identify and concentrate on interventions that are successful.  Therapists can avoid wasting time with strategies that do little to alter behavior.

Related resource: Top 20 Online Applied Behavior Analysis Bachelor’s Degree and BCaBA Coursework Programs


This model is a form of a research protocol called Single Subject Experimental Design (SSED). Single Subject Research Designs are common in special education and in clinical settings. In a SSED, the individual serves as their own control. Their performance is not compared to a group or another individual.

ABAB and ABA are not acronyms as such but refer to the stages of the model.

  • “A” is the dependent variable.  It represents the initial unaltered behavior, and that becomes a baseline for the study.
  • “B” is the independent variable or the treatment phase

The rationale behind a single subject designs are:

  • Prediction
  • Verification
  • Replication

Even though an SSED implies there is only one subject, in a research study, there are many different subjects using the same design.  It is still considered a single subject design though since the individual is their own control.

AB Design

In a basic AB design psychology experiment, there is a baseline (A) and an intervention (B).  If A changes after the implementation of B, a researcher could conclude that B caused a change in A.  Unfortunately, this is oversimplified thinking, and a strong conclusion is difficult to make.  The AB design does a poor job of controlling for threats to internal validity.

ABA Design

So, in an ABA research design, the initial behavior is altered by the intervention and then the intervention is withdrawn to see if the behavior returns to the baseline level.  This is also known as a reversal design.  If the dependent variable changes when the intervention takes place and then returns to baseline, there is further evidence of a treatment effect.   Since the ABA design has a high degree of experimental control, there is confidence that treatment effects are actually the result of the treatment and not something else.

ABAB Design

The ABAB design is the reintroduction of the intervention after the return to the baseline to judge the strength of the intervention and determine if there is a functional relationship between A and B. The ABAB design definition includes:

  • A- Baseline period and data collection
  • B- Intervention
  • A- Removal of the intervention, back to baseline
  • B- Introduction of the intervention again

Some interventions may increase over time while others grow weaker as the person being studied becomes accustomed to the intervention.

The ABAB design can be considered a type of time-series design.  This means researchers can use the same statistical procedures with ABAB that they do with a time series analysis.

Related Resource: Understanding the Difference between an ABA Therapist and a BCBA

How the ABA Model is Used

These research methods are also by therapists to discover treatments for patients with target behavior that affects their life activities. It is especially helpful when working with individuals with intellectual and developmental disabilities.  It is also used in the treatment of individuals with autism spectrum disorder because it isolates one behavior to address.

An example cited in one article is that of children asked to read a paragraph that included text only. The children were tested on their understanding of the information. Then, another paragraph including an illustration was given to the children to read. Again, they were tested to see if their level of understanding increased. Finally, they were given another paragraph that contained only text and retested to see if their grasp of the information returned to the initial test results.  Using the ABA design, the therapist can evaluate the effects of treatment related to baseline responding.

According to an article in the US National Library of Medicine, the primary requirement to judge the effectiveness of this model is the ability of the researcher to replicate the results. A study of the same behavior in several different people should elicit the same results. That replication becomes the basis for identifying the intervention as a universal method of treatment.

How the ABAB Model is Used

An ABAB reversal design can also work when trying an intervention to help reduce self-injurious behavior.  The individual engages in hair pulling and biting.  After the initial baseline phase, the therapist begins the intervention program.  The therapist continues to collect data on the self injurious behavior.  The therapist then stops the intervention phase, but still continues to collect data on the same behavior.  Finally, the therapist reintroduces the intervention and completes their statistical analysis.  If the behavior improves with the intervention and reverts back to the initial baseline numbers when the intervention is removed, then it is easy to verify treatment effects on the behavior.  The intended behavior modification is likely strengthened.  This type of experiment can also be used for anxiety disorders and feeding disorders.


The ABA design psychology experiment allows researchers to isolate one behavior for study and intervention. That decreases the chances of other variables influencing the results. It is also a simple way to assess an intervention.  If only one thing is changing at a time, it is easy to decipher if an intervention is working.  If the behavior doesn’t after the intervention is removed, then something else must be causing the change in behavior.  The design is pretty straightforward.  The model allows therapists to identify successful interventions quickly.

The main advantage of the ABAB model is that it ends “on a positive note” with the intervention in place instead of with its withdrawal.  Another advantage is that the ABAB design psychology experiment has an additional piece of experimental control with the reintroduction of the intervention at the end of the study.  Some researchers believe ABAB is a stronger design since it has multiple reversals.


One of the major drawbacks to this model is contained in the question, “what if the behavior does not change with the intervention?” In the Randomized Control Trials, that outcome would be supported by similar findings among many people, but the lack of results invalidates a study of one individual. For instance, the researcher would not know if other variables had been introduced.

The other major disadvantage is the ethical problem of identifying a successful intervention and then withdrawing it.  The ABA and ABAB design can’t be used with variables that could cause irreversible effects.  It also can’t be used when it would be unethical or unsafe for an individual to revert back to their baseline condition.   It can also be hard to rule out a history effect if the dependent variable doesn’t return to its original state when the treatment or therapy is removed.

Fortunately, there are options when an ABA or ABAB design isn’t feasible.  A multiple baseline design can be used when there is more than one individual or behavior in need of treatment.  This design can also be used if the effects of the independent variable can’t be reversed.  The alternating treatments design can be used when you want to determine the effectiveness of more than one treatment.  The changing conditions design can be used to study the effect of two or more treatments on the behavior of an individual.


Behavioral analysis is a therapy used with people of different ages and cognitive abilities. Often, therapists work with a patient for a long time to find an intervention that succeeds in modifying a troublesome behavior. The use of the ABA and the ABAB models can shorten the time of treatment and increase the chances of a good outcome for clients of mental health practitioners.