under 30–36 months of age. There is overlap in the levels of intensity with which the models are implemented, and the measures of outcome differ widely across interventions.
In addition, as summarized in Figures 1–1, 1–2, and 1–3 (in Chapter 1), studies that addressed general aspects of interventions consistently had methodological limitations that were often even more common than in studies about interventions for narrower target areas (see Kasari, 2000). These limitations in part reflect the tremendous scope required in carrying out research concerning comprehensive intervention programs. On the whole, issues related to internal and external validity were addressed only minimally in about 80 percent of the published studies, with measurement of generalization outside the original setting occurring only minimally in 70 percent of the research reports. Given the difficulty and the cost in time and money of such studies, it seems most useful to consider alternative methods to addresses these concerns.
The models presented positive and remarkably similar findings, which included better-than-expected gains in IQ scores, language, autistic symptoms, future school placements, and several measures of social behavior. Although possible changes in diagnosis are implied, these have not been systematically documented or supported with independent observations or reports. Considered as a group, these peer-reviewed outcome studies suggested positive change in the language, social, or cognitive outcomes of children with autistic spectrum disorders who received intensive early intervention beginning at young ages. However, only three of the studies (plus one follow-up) had comparison group data, and only one of the studies (Smith et al., 2000b) practiced random assignment of children to conditions, and this procedure was complex. Pre-post assessment measures reflected positive outcomes for the majority of children receiving intervention, and most children showed some progress. However, there was almost no information on the contribution of the other interventions and therapies in which the children participated.
In sum, it appears that a majority of children participating in comprehensive behavioral interventions made significant progress in at least some developmental domains, although methodological limitations preclude definitive attributions of that progress to specific intervention procedures.