Over the past 40 years, an extensive body of literature has documented the successful use of ABA-based procedures to reduce problem behavior and increase appropriate skills for individuals with intellectual disabilities (ID), autism, and related disorders. The literature consists of numerous controlled studies employing single-case experimental designs, consecutive controlled case-series studies, controlled group studies, and some randomized controlled trials.

Types of Research Designs:

A number of different research designs are used to evaluate treatments and answer other questions about treatment procedures. Each type of design has its own scientific and practical strengths and limitations, and each is ideally suited to answer particular types of questions. The designs are discussed further below.

Single-case experimental designs:

Many studies demonstrating the outcomes obtained with ABA-based procedures use single-case experimental designs (also termed “single-subject designs”; Kazdin, 2010 & 2013) because this type of design is ideal for examining how the behavior of an individual changes as a function of changes in the environment – which is the subject of interest in the field of ABA. These studies often include a small number of individuals (typically between one to four). It should be noted that published studies using single-case experimental designs are not the same as “case reports” (often seen in clinical journals), which are typically simply descriptive in nature. Rather, studies using single-case designs are controlled studies where treatment is applied in a manner that allows one to demonstrate that the treatment was responsible for the change in behavior. These studies are methodologically rigorous because they involve direct observation of behavior and objective data collection where behaviors are defined and counted (often using a computerized data collection system). A second observer also collects data independently to ensure reliable and accurate data collection.

The most common type of single-case design is a reversal design, which involves the following: a pre-treatment baseline level of behavior is obtained, then treatment is applied, and after a change is observed, the treatment is withdrawn, then reapplied to replicate the treatment effect (Kazdin, 2010; Kratochwill & Levin, 2010). The “replication” of the treatment effect illustrates that the treatment (and not some other event) is responsible for the change. This type of design has excellent “internal validity,” which refers to the extent to which the change in behavior can be attributed to the intervention and not some other variable. Single-case designs are limited, however, in that one cannot determine the extent to which the findings for one study are applicable to other individuals or situations (that is, it has weak “external validity”). It is possible that only cases for which treatment was successful were included in the published study (a concern termed “publication bias”). On the other hand, the ABA literature spans four decades and describes the efficacy of these treatments across a wide range of populations, settings, and problems. Collectively, this extensive body of literature provides strong evidence supporting the external validity of ABA-based interventions.

In the field of ABA, single-case experimental designs are not reserved for exclusive use in research studies. Rather, their use represents good clinical practice. During assessment, single-case designs permit one to identify what factors cause the behavior in question. These findings are then prescriptive for developing an individualized treatment. In addition, single-case designs enable one to determine whether a prescribed treatment (or what particular elements of a treatment) is responsible for behavior change. Isolating the active ingredients of treatment is crucial in saving time and resources.

Consecutive controlled case series designs:

Consecutive controlled case-series studies describe a series of cases where single-case experimental designs were used (see Rooker et al., 2013 for a recent example). These studies describe all individuals encountered who were treated with a certain procedure (regardless of whether the treatment was effective or not), and thus have better external validity than cases involving fewer participants. Because all the cases in the series evaluated treatment using single-case experimental designs, consecutive controlled case-series studies have excellent internal validity as well. Moreover, because a large number of individuals are included, they provide an opportunity to answer other questions, including determining what characteristics predict good outcomes. Several large scale consecutive controlled case series studies describing ABA-based assessment and treatment procedures have been published, and their findings nicely correspond to the broader body of single-case studies describing smaller numbers of individuals.

Group designs:

In contrast to single-case experimental designs where the individual’s behavior change during treatment is compared to his/her own behavior without treatment, group designs evaluate treatments based on a comparison of a group of individuals receiving one treatment relative to another similar group of individuals who received no treatment (or a different treatment; Kazdin, 2003). In contrast to single-case designs, where the behaviors of an individual are observed extensively and repeatedly (often for many hours or days) before and after treatment, group designs involve fewer observations of each individual in the group but obtain these measures across large numbers of individuals. Statistical analyses are used to determine whether overall differences between the groups are large enough to conclude that they are not due to normal variation or “chance” (Cohen, Cohen, West, & Aiken, 2003).

The most rigorous type of group design is a randomized controlled trial, which involves randomly assigning participants to a particular group (e.g., treatment or no treatment), and observers who evaluate the outcomes of the treatment do not know whether the participant received treatment or not (i.e., observers are “blinded”). When certain types of treatments, such as medications are being evaluated, the participant may also be “blind” to which group s/he is assigned through the administration of an inactive pill (a placebo). Several group studies describing comprehensive ABA-based interventions for individuals with autism have been published, including some that have used randomization (e.g., Sallows & Graupner, 2005; Smith, Groen, & Wynn, 2000). The most appropriate design to use in a particular situation depends on numerous factors, including the research question, consideration of the relative costs and benefits to participants, and the current state of knowledge about the topic of interest.

Findings from Controlled Studies Employing Single-Case Experimental Designs:

Small-n Controlled Studies:

Over a thousand studies reporting on ABA-based assessment and treatment techniques have been published since the 1960’s. As discussed in the “types of research designs” section above, these controlled studies have strong internal validity as they use experimental designs that permit one to conclude that the intervention was responsible for the change in behavior. Studies on topics relevant to the use of ABA with persons with intellectual and developmental disabilities are most frequently published in journals such as: Behavioral Interventions, Journal of Applied Behavior Analysis, Journal of Autism and Developmental Disorders, Journal of Intellectual Disability Research, Research in Developmental Disabilities, Research in Autism Spectrum Disorders. Topics of these studies include communication training, social skills training, behavioral assessment and treatment of problem behavior (e.g., self-injury, aggression), educational instruction, early intensive behavioral intervention, etc. For further information, the reader is referred to these journals or to an on-line search engine (i.e., PsychINFO, Google Scholar).

Consecutive Case-Series Studies:

As discussed on the types of research designs section above, consecutive controlled case-series studies describe a series of cases where single-case experimental designs were used with all individuals encountered (regardless of whether the treatment was effective or not).

Functional Analysis of Problem Behavior:

Focused ABA interventions for problem behavior are designed for each individual based on an understanding of what antecedents may “trigger” problem behavior and what consequences may reinforce (reward) it. Functional behavioral assessment can be performed using a range of procedures, including interviews, questionnaires, direct observation in the individual’s natural setting, and / or systematically presenting situations that can function as potential triggers or rewards and observing and recording how behavior changes with these events. This latter type of procedure, called a functional analysis, is the most rigorous type of functional behavioral assessment. In most cases, the results can reveal why problem behavior occurs and persists – and thus provides a foundation for focused interventions targeting these behaviors.

Literature reviews by Hanley, Iwata, and McCord (2003) and Beavers, Iwata, and Lerman (2013) collectively identified 435 peer-reviewed articles where functional analysis of problem behavior was reported. Studies listed below represent a sample of the large-scale consecutive controlled case series studies involving functional analysis. These studies demonstrate that functional analysis is highly effective in identifying the controlling variables for problem behavior.

Functional analysis across a variety of settings (inpatient, residential)
Participants: 154 cases
Results: Conclusive assessment results in over 90% of cases
Reference: Iwata BA, Pace GM, Dorsey MF, Zarcone JR, Vollmer TR, Smith RG, Rodgers TA, Lerman DC, Shore BA, Mazalesk JL, et al. (1994). The functions of self-injurious behavior: An experimental-epidemiological analysisJournal of Applied Behavior Analysis, 27(2), 215-240.

Functional analysis in school settings
Participants: 69 cases
Results: Conclusive assessment results in over 90% of cases
Reference: Mueller MM, Nkosi A, Hine JF. (2011). Functional analysis in public schools: A summary of 90 functional analyses. Journal of Applied Behavior Analysis, 44(4), 807-818.

Functional analysis of severe problem behavior
Participants: 176 cases with severe problem behavior
Results: Conclusive assessment results in over 90% of cases
References: Hagopian LP, Rooker GW, Jessel J, DeLeon IG. (2013). Initial functional analysis outcomes and modifications in pursuit of differentiation: A summary of 176 inpatient cases. Journal of Applied Behavior Analysis, 46(1), 88-100.

ABA-Based Focused Treatment for Problem Behavior:

Studies employing rigorous single-case experimental designs describing ABA focused interventions for problem behavior have been reported for four decades. The following sample of large-scale consecutive controlled case series studies provide further support for the effectiveness of these interventions. Findings from these studies parallel findings from reviews and meta-analysis of small-n studies.

Functional communication training for treatment of problem behavior
Participants: 21 inpatient cases with IDD
Results: 80% or greater reduction in problem behavior in 90% of cases
Reference: Hagopian LP, Fisher WW, Sullivan MT, Acquisto J, LeBlanc LA. (1998). Effectiveness of functional communication training with and without extinction and punishment: A summary of 21 inpatient cases. Journal of Applied Behavior Analysis, 31(2), 211-235.

Function-based treatment for severe problem behavior
Participants: 138 inpatient cases with IDD
Results: 90% or greater reduction in problem behavior in over 83% of cases
Reference: Asmus JM, Ringdahl JE, Sellers JA, Call NA, Andelman MS, Wacker DP. (2004). Use of a short-term inpatient model to evaluate aberrant behavior: Outcome data summaries from 1996 to 2001. Journal of Applied Behavior Analysis, 37(3), 283-304.

Functional-based treatment delivered by care providers (mostly parents) for severe problem behavior
Participants: 42 outpatient cases with IDD
Results: 80% or greater reduction in problem behavior in 95% of cases
Reference: Kurtz PF, Fodstad JC, Huete JM, Hagopian LP. (2013). Caregiver- and staff-conducted functional analysis outcomes: A summary of 52 cases. Journal of Applied Behavior Analysis, 46(4), 738-749.

Functional communication training for treatment of severe problem behavior
Participants: 50 inpatient and outpatient cases with IDD
Results: 80% or greater reduction in problem behavior in 86% of cases
Reference: Rooker GW, Jessel J, Kurtz PF, Hagopian LP. (2013). Functional communication training with and without alternative reinforcement and punishment: An analysis of 58 applications. Journal of Applied Behavior Analysis, 46(4), 708-722.

Review Papers:

Broadly speaking, review papers summarize the published literature on a specific topic (e.g., diagnosis, type of assessment or treatment procedure). The reader is referred to recent reviews on comprehensive and focused ABA-based interventions for problems associated with autism:

Recent reviews on ABA-based procedures for persons with intellectual and developmental disabilities (IDD):

Review articles indicating that treatments for autism and intellectual disability derived from ABA-based procedures are empirically supported treatments also have been published in non-behavioral journals. For example, the journal Current Opinion in Psychiatry is a journal designed to assist clinicians and researchers by synthesizing the psychiatric literature. An article that reviewed the assessment and treatment of individuals with intellectual disabilities and psychiatric disorders concluded that: "Interventions based on applied behavior analysis have the strongest empirical basis, although there is some evidence that other therapies have promise" (Sturmey, 2002, p. 489). Also, in the journal Pediatrics, the official journal of the American Academy of Pediatrics (AAP), an article offering guidelines on scientifically supported treatments for childhood psychiatric disorders concluded: "The most efficacious psychosocial treatment for autism is applied behavior analysis" (Lilienfeld, 2005, p. 762). The AAP issued a Clinical Report in Pediatrics regarding the management of children with autism, and the authors noted: “Children who receive early intensive behavioral treatment have been shown to make substantial, sustained gains in IQ, language, academic performance, and adaptive behavior as well as some measures of social behavior, and their outcomes have been significantly better than those of children in control groups” (Myers, & Johnson, 2007, p. 1164). In the Archives of Pediatric and Adolescent Medicine, Barbaresi et al. (2006) concluded, “ABA should be viewed as the optimal, comprehensive treatment approach in young children with ASD.”

Review papers finding support for ABA can be found in the following non-behavioral journals:

  • Current Opinion in Psychiatry (Grey & Hastings, 2005; Sturmey, 2002)
  • Scientific Review of Mental Health Practice (Herbert, Sharp, & Gaudiano, 2002)
  • American Journal on Mental Retardation (Kahng, Iwata, & Lewin, 2002)
  • Psychiatric Times (Erickson, Swiezy, Stigler, McDougle, & Posey, 2005)
  • Archives of Pediatric and Adolescent Medicine (Barbaresi, Katusic, & Voigt, 2006)
  • Child and Adolescent Psychiatric Clinics of North America (Doehring, Reichow, Palka, Phillips, & Hagopian, 2014)


In general, meta-analysis involves quantitative re-analysis of data reported in published studies. This requires standardizing treatment outcomes by statistically calculating “effect sizes” obtained within each study, for the purpose of evaluating data obtained across a group of studies on a particular treatment.

Similarly, seven meta-analyses (Campbell, 2003; Didden, Duker, & Korzilius, 1997; Harvey, Boer, Meyer, & Evans, 2009; Heyvaert, Maes, Van den Noortgate, Kuppens, & Onghena, 2012; Lundervold & Bourland, 1988; Ma, 2009; Weisz, Weiss, Han, Granger, & Morton, 1995) that collectively analyzed hundreds of studies concluded that ABA-based procedures were more effective for reducing problem behavior displayed by individuals with ID (as well as typically-developing individuals) than were alternative treatments. The large body of literature reviewed in these studies provides empirical evidence indicating that focused ABA interventions are effective at assessing and treating a variety of socially important behaviors emitted by individuals with a variety of diagnoses.

Furthermore, several meta-analytic studies also have found comprehensive ABA-based approaches for educating children with autism result in favorable outcomes (Eldevik, Hastings, Hughes, Jahr, Eikeseth, & Cross, 2010; Makrygianni & Reed, 2010; Reichow, 2012; Reichow, Barton, Boyd, & Hume, 2012; Virues-Ortega, 2010). In a recent meta-analytic study involving 22 studies, Virues-Ortega (2010) concluded: “Results suggest that long-term, comprehensive ABA intervention leads to (positive) medium to large effects in terms of intellectual functioning, language development, and adaptive behavior of individuals with autism” (p. 397).

Systematic Evaluative Reviews:

Systematic approaches for formally evaluating a body of research have been developed to determine if a particular intervention can be characterized as “empirically supported” or “established” based on the number, quality, and outcomes of published treatment studies. These efforts have been undertaken for the purpose of guiding clinical practice, influencing regulations and standards, providing priorities for funding (for both research and treatment), and guiding professional training (see Mesibov & Shea, 2011). For example, the American Psychological Association (Task Force Promoting Dissemination of Psychological Procedures, 1995) described a process to identify “empirically supported treatments.” Those interventions with the highest level of support are characterized as “well-established” (Chambless, et al, 1996).

Evaluations of the most commonly used focused ABA-based interventions (functional communication training and noncontingent reinforcement) indicated that these interventions meet criteria as “well-established” empiricially supported treatments (Carr, Severtson, & Lepper, 2009; Kurtz, Boelter, Jarmolowicz, Chin, & Hagopian, 2011). ABA-based treatments for pica (Hagopian, Rooker, & Rolider, 2011), and for treatment of phobic avoidance (Jennett & Hagopian, 2008) displayed by individuals with intellectual disabilities also have been characterized as “well-established.”

The National Standard Project of the National Autism Center developed a similar model to evaluate interventions for problems associated with autism (2009), which used the term “established” to describe interventions with the highest level of support. Using their evaluative method, the National Autism Center (2009) characterized comprehensive ABA-based interventions as being “established” treatments for autism.

Wong and colleagues (2013), as part of the Autism Evidence-Based Practice Review Group, describe a process for the identification of clinical practices that have sufficient empirical support to be termed “evidence-based.” The group stated in regards to the strength of evidence of ABA “Twenty-seven practices met the criteria for being evidence-based (see table 7, page 20)….evidence-based practices consist of interventions that are fundamental applied behavior analysis techniques (e.g., reinforcement, extinction, prompting), assessment and analytic techniques that are the basis for intervention (e.g., functional behavior assessment, task analysis), and combinations of primarily behavioral practices…”

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