intervention (Kasari, 2000). Measurement of potential treatment effects (e.g., developmental assessments, family measures) occurs before the educational intervention begins and again at the end of the intervention; the measurement is blind to which group a participant has been assigned to. Assuming that the groups are equivalent on the pretest measures, differences at the end of the intervention are attributed to the treatment. As noted above, the purpose of random assignment is to control for or reduce the likelihood that confounding variables (e.g., very determined parents requesting a particular treatment) would account for differences in outcomes for the treatment and contrast groups.
Reviews of the literature to date (Rogers, 1998) and individual papers prepared for this committee (Kasari, 2000; Wolery and Garfinkle, 2000) show that the randomized clinical trial model has only rarely been used to determine treatment outcomes (see Jocelyn et al.  and Smith et al.  for exceptions). Other studies have attempted to address the research question of treatment effectiveness by employing quasi-experimental designs (Cook and Campbell, 1979) in which nonrandomized control or contrast groups are used as a basis for gauging treatment effects (Fenske et al., 1985). Another approach has been to use single group designs in which the changes in children’s development while they are in the program are compared with children’s rates of development before they entered the program, or to the rate of development of typically developing children (Harris et al., 1991; Hoyson et al., 1984). These designs, while providing some information about treatment outcomes, may not control for important confounding variables, such as subject selection and nonspecific or placebo effects (see Campbell and Stanley’s  classic paper on group experimental methodology).
For programs providing treatment to young children with autistic spectrum disorders and their families, random assignment is often a difficult procedure. By its very nature, it requires that some children and families be assigned to an alternative treatment condition. Unless two treatments of equal potential value can be compared, such assignment creates the ethical issue of not providing the most promising treatment to children who might benefit. An argument is sometimes made (as it often is in medical treatment studies) that until a treatment is supported by a randomized clinical trial, the evidence for effectiveness of the treatment does not exist. In addition, when children are randomly assigned to two different treatment conditions, a researcher still must closely assess the experiences of the child and family, because families may seek and obtain services for their children outside of the treatment study. Ideally, children and families could be assigned to equally attractive alternative treatments, so that the research question changes from one of single treatment effectiveness to treatment comparison. However, this approach would require the availability of two different and equally strong programs,