parents can do to help their children. (Issues relating to diagnosis are discussed in detail in Chapter 2.)

In the early 1990s, the Checklist for Autism in Toddlers (CHAT) was developed as a creative, theoretically based attempt at a public health screening instrument (Baron-Cohen et al., 1992). With follow-up, however, it appeared that the sensitivity of the CHAT in identifying autism in nonreferred children was far too low to be considered an appropriate screening tool (Baird et al., 2000). Nevertheless, the instrument has made a significant contribution as a first step in this area. The techniques described in the CHAT may also be helpful in providing a primary health care professional with some behaviors on which to focus during screening (e.g., eye contact, pretending). Pilot data from a modification of this instrument, the M-CHAT, are in press.

Other screening tools, such as the Pervasive Developmental Disorders Screening Test (PDDST; Siegel, 1998) and the Screening Tool for Autism in Two Year Olds (STAT, Stone, 1998), are used to determine whether further diagnostic assessments are merited after a concern has arisen. Each of these instruments has promise: an initial empirical evaluation of the STAT has just been published (Stone et al., 2000); an evaluation of the PDDST is not yet available. The Autism Screening Questionnaire (ASQ; Berument et al., 1999) was developed for screening research participants 4 years of age and older. It has not yet been tested with younger children or with families who have not already received a diagnosis of autistic spectrum disorder. Chapter 2 provides more information about screening, as do the interdisciplinary practice parameter guidelines described by Filipek and colleagues (2000). An adequate screening instrument is not currently available either for public health screening or for a brief assessment when a concern arises. Addressing this need is a high priority for researchers. It involves determining how specifically the features of autistic spectrum disorders can be defined in toddlers and contrasting the benefits of this approach with more general identification of risk status.

Research in diagnosis is at a quite different stage. Well-standardized and documented diagnostic instruments have been available for years. These include the Childhood Autism Rating Scale (CARS; Schopler et al., 1988), the Autism Diagnostic Interview-Revised (ADI-R; Lord et al., 1993), and the Autism Diagnostic Observation Schedule (ADOS; Lord et al., 2000). Although there are many ways that these instruments could be improved, their ability to document autism in a reliable and standardized way has been demonstrated. There are also numerous other instruments, including the Autism Behavior Checklist (Krug et al., 1980) and the Gilliam Autism Rating Scale (Gilliam, 1995), about which there are more questions regarding the degree to which their scores reflect accurate diagnosis.

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