A-B-A Design in Psychology

Determining the Effectiveness of Treatment on Behavior

A-B-A design used to evaluate effective of interventions on education, psychology, and special need children.
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People often regard psychology as an inexact science that doesn't have the same measures or values as, say, chemistry or biology. This is largely an unfair assessment, particularly in regards to research where psychologists rely on the same science-based evidence as any other investigator.

One of the more common ways to do so is with an analysis model known as A-B-A design. It is used for both the experimental analysis of behavior (which aims to draw associations between situations and behaviors) and applied behavior analysis (in which techniques are applied based on principles of learning).

It is an approach to research used popularly in education, counseling, speech pathology, and both human and non-human behavioral research. A-B-A is one of the techniques psychologists will use when working with children with autism.

Understanding A-B-A Design

A-B-A design is a compellingly simple model to understand. It involves establishing a baseline condition (the "A" phase), introducing a treatment or intervention to effect some sort of change (the "B" phase), and then removing the treatment to see if it returns to the baseline.

A-B-A design allows researchers to evaluate how effective a treatment is. If the behavior completely reverts to the baseline following the withdrawal of treatment, then the scientists can be pretty confident that the treatment works. If the same effect is restored after the treatment is reapplied, the confidence in the treatment is greatly increased.

Examples of A-B-A Design

A-B-A design in one of several different models used in single-subject research.

Single-subject research is one in which a subject—whether an individual or group—serves as its own control. It is can be used to rigorously test the success of an intervention on a person, school, or community and provide evaluative measures as to general effectiveness of that intervention

Let's say, for example, that we are conducting an experiment to determine the impact of illustrations on reading comprehension among third-graders.

Under the A-B-A design model:

  • The third-graders would start by reading a text-only paragraph (the "A" phase) and be tested to assess their reading comprehension.
  • The same group would then be asked read another paragraph, this time with an illustration (the "B" phase), and be tested again.
  • To complete the A-B-A model, the students would be provided yet another text-only paragraph and be tested one final time.

A review of scores would provide the investigators with insights into the impact of the intervention, if any.

Key Features of A-B-A Design

The A-B-A model shares many of the characteristics of other single-subject research methods:

  • A-B-A design allows researchers to obtain repeated measurements in order to establish consistent patterns in behaviors.
  • It allows researchers to measure behavior accurately under controlled conditions with consistent values.
  • It focuses on how a single variable influences behavior rather than a set of variables.
  • It is not so concerned at how the results compare to the general population but rather how a controlled intervention affects the subject and subject alone.

A-B-A-B Design

An extension of the model is A-B-A-B design. This involves measuring the baseline (the "A" phase), introducing the treatment (the "B" phase), withdrawing the treatment, and reintroducing it one final time.

This is considered a confirmatory model that it not only tells us if an effect can be repeated but how robust that effect is.

In some cases, the effect may be short-lasting and wane over time. In others, it may intensify the more an individual or group is exposed to that treatment.


Byiers, B.; Reichle, J.; and Symon, F. "Single-Subject Experimental Design for Evidence-Based Practice." Am J Speech Lang Pathol. 2012; 21(4):397–414; DOI: 10.1044/1058-0360(2012/11-0036).

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