Autism is a pervasive developmental disorder defined behaviorally and characterized by impairments in three areas: social interaction, reciprocal verbal and nonverbal communication and the range of interests and activities (1). Although recognition of this disorder may have its origins in Jean-Marc Gaspard Itard’s description of the “wild boy of Aveyron” from 1801 (2), the first formal account of autistic individuals was published by Leo Kanner in 1943. The current definition of autism, although consistent with the deficits observed in Kanner’s original group of children, has been refined and broadened. Nowadays, persons with autism are considered to have one of the neurodevelopmental disorders that have such wide range of behavioral consequences and severity that they are collectively referred to as pervasive developmental disorders (PDDs) in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders, Revised Text (1).

Autism is one of the most severe developmental disorders. It is also often called an “enigma” due to the fact that so far scientists have found no answers to many questions related to the disorder. Nevertheless, nearly 70 years which have passed since the first systematic description of children with autism, and over 50 years devoted to the application of behavioral techniques to solving human problems, have brought forth a substantial body of knowledge about effective methods of helping autistic people. This knowledge is well grounded thanks to, among other factors, the fact that the theory of autism and behavioral therapy is entrenched in empirical research, while the combination of theory and research reflects clinical practice.

Scholarly research shows that early intensive behavioral therapy can lead to significant and clinically important changes in an autistic child’s cognitive, social and emotional functioning (3-5). A survey of about 500 publications on the use of methods based on the applied behavior analysis (ABA) has shown that behavioral techniques are effective in teaching children with autism as well as in their adaptation to independent life (6). What is more, behavioral therapy is recommended by government organizations in the USA and Europe (7, 8) as the leading form of treatment administered to children with autism. The behavioral approach includes a few different “variants” which differ in the techniques they use and in the logistics of the services they offer (9-11). However, what the programs offering behavioral therapy have in common is the fact that they view autism not as a hypothetical construct but as a set of behavioral deficits and excesses, and that they apply the learning theory to their therapeutic work (12).

Ivar Lovaas and Tristam Smith (13) have described four tenets of their theory in the article „A comprehensive behavioral theory of autistic children: Paradigm for research and treatment”. First, behavior of people with autism does not differ from behavior of other people, and it obeys the basic principles of behavior. When reinforcement and extinction are applied, the learning curves of people with autism are very similar to those of other people. The range of reinforcers, which is at first very scanty for autistic people, can be effectively broadened by the application of procedures which combine initially neutral stimuli (such as praise) with primary reinforcers (such as food) or with other, already established reinforcers (such as toys). Learning difficulties can be lessened by discrimination training, especially during imitation and match-to-sample exercises in the educational programs.

Second, people with autism have several behavioral deficits and excesses rather than one central disfunction whose correction would lead to general and extensive improvement. This assumption is based mainly on the results of research on generalization, which demonstrates clearly that people with autism show the high specificity of their behavior rather than its generalization. Transfer of skills from one kind of behavior to another or from one stimulus to another is possible, but only after the teaching procedures have been planned carefully and generalization has been included in the therapy. This assumption is reflected in clinical work very clearly: therapists should build for a given child a “pyramid of skills”, beginning at the base – one brick after another – teaching more complicated skills on top of what has already been learnt.

Third, people with autism can learn in an environment which is specifically adjusted to their needs. This environment should only differ so far from normal surroundings as to be “functional”, i.e. understood and predictable for an autistic person. Often the modifications include making certain stimuli more distinct (for instance by uttering simpler statements to the child), making use of motivational systems and of visual stimuli (such as pictures) supplementing auditory stimuli.

Fourth, the difficulty autistic people have with functioning in the normal environment and their success in the special environment show that autism ought to be regarded as a disorder consisting of maladjustment of the neural system to the typical living conditions, rather than as a disease which can be cured. Therefore, therapeutic work should rely primarily on creating special conditions for a child with autism, where they shall be able to function well and learn, and only secondarily on gradually accustoming them to life in the typical environment, where they may also support themselves with certain assistive technology (such as using a communication board while shopping).

To sum up, Lovaas & Smith (13) propose that autistic people ought to be regarded, especially when it comes to therapeutic work, not as “different, abnormal, and standing out”, but rather as being on the same continuum of functioning as other people, only at its end. Therefore the task of behavioral therapists is to “move” autistic people in the direction of the center of this continuum, by working systematically on individual deficits and excesses.

Effective intervention is an even more urgent issue, when one takes into consideration the epidemiological reports concerning the frequency of pervasive developmental disorders. The review of the range of prevalence estimates for autism and other PDDs comes from a series of publications by Fombonne (14-18). In the last article, Fombonne reports the occurrence of PDDs in children under the age of 8 years to be of the order of 60 to 70 per 10,000 children. Several factors could have contributed to an increased prevalence of autism, but most likely this change is probably attributable to improved detection and changes in diagnostic criteria. Regardless of the underlying reasons, the issue of early identification of and intervention in autism is of paramount importance.

Early Intensive Behavioral Intervention (EIBI) is a form a comprehensive treatment based on principles of applied behavior analysis and administered to children with autism. According to Green, Brennan & Fein (19) it is characterized by: 1) individualized and comprehensive programing of educational goals, 2) use of behavioral techniques, 3) close supervision of service delivery by individuals trained in the ABA, 4) programing of therapeutic goals based on knowledge of developmental milestones, 5) close collaboration with the parents in planning and conducting the therapy, 6) initially teaching the child on a one-to-one basis in a natural environment, with a gradual transition to a group setting, 7) intensive teaching (i.e., 20-30 hours per week, all year round), 8) extended duration (i.e., at least 2 years in most cases), and 9) early start of intervention (i.e., before the child turns 3 years old). EIBI has been shown to be effective and has been classified by Rogers and Vismara (20) as a “well established” treatment based on the criteria for empirically-validated treatments (21). Below, we present three publications that provide evidence for the recommendation that EIBI should be a treatment of choice for children with autism. Two of them are meta-analyses and one is an experimental study.

In the last 30 years meta-analysis has been accepted in the social and health sciences as a very useful and helpful research methodology to quantitatively integrate the results from different studies. In a meta-analysis results of every study are quantified by means of an effect-size index (e.g. standardized mean difference), enabling us to give the study results in the same metric (22, 23). Typically, in meta-analysis two tests are conducted: test of homogeneity (using the Q-statistic and I²) and effect size (using e.g. Hedges’s g) (22). The Q-statistic test only informs us about the presence or absence of heterogeneity. The I² reports on the extent of such heterogeneity (between-study variance).

First meta-analysis was conducted by Edelvik et al. (24). The selection of studies for this meta-analysis involved eight inclusion criteria:

– the participants received behavioral intervention,

– the participants receiving EIBI were on average between 2 and 7 years old when the treatment started,

– the participants were diagnosed with autism or PDD-NOS,

– a full-scale measure of intelligence (IQ) and/or a standardized measure of adaptive behavior such as the Vineland Adaptive Behavior Scales (VABS) were used,

– the duration of intervention was between 12 and 36 months,

– the study was a group study, not a case study,

– the study included either a control or a comparison group,

– the results were published in a peer-reviewed journal.

Nine research reports met all inclusion criteria, so additional detailed information was obtained by contacting the authors of each study (provide the age, IQ, and adaptive behavior scores for the participants). Not all authors collected both IQ and Adaptive Behavior Composite (ABC) data. Additionally, the authors measured intelligence with various tests (e.g. Bayley Scales of Infant Development, Wechsler Preschool and Primary Scale Intelligence-Revised etc.). If the participant scored on a test below the norm, researchers calculated a ratio IQ score by dividing the obtained mental age with chronological age and multiplying by 100. All of the tests have been validated for children with pervasive developmental disorders. All studies used the VABS (Vineland Adaptive Behavior Scale) for measuring the adaptive behavior. The content and scales of the VABS were organized within a four domain structure: communication, daily life, socialization and, for children younger than 6 years old, motor skills (24, 25). The VABS is the best available instrument for assessing adaptive behavior in children with pervasive developmental disorders and/or mental retardation.