FIGURE 1–2 External validity.

NOTES: Level I represents the strongest methodological controls and IV the least strong (see Box 1–1); N is the number of studies.

SOURCES: For social studies, McConnell (1999); for communication studies, Goldstein (1999); for problem behavior studies, Horner (2000); for intervention studies, Kasari (2000); for sensory-motor studies (Baranek, 1999).

fragmented across studies. Today, that information would have been an expected component of a research design from the start.

Clinical research always involves compromises based on such factors as access to populations and acknowledgment of clinical needs; often, expense is also considered. Even today, there are very different standards across journals and across research communities as to what are considered unacceptable compromises and what is deemed a necessary part of dealing with complex questions. One of the goals that arose from this review was to identify ways of bridging gaps between perspectives in setting guidelines for research about autism. The committee recognized that a range of emphases and designs is important for different questions. Because of the varied nature of the research, the guidelines presented in Box 1–1 were used to characterize the research reviewed. In this way, the strengths and limitations of individual studies could be considered when deriving conclusions based on the consistencies and inconsistencies observed across investigations and theories.

Evidence concerning the effectiveness of instructional and comprehensive programs, strategies, and approaches to intervention for young

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