The Childhood Asperger Syndrome Test (CAST)

A D D R E S S Correspondence should be addressed to: C A R R I E A L L I S O N , Autism Research Centre, Douglas House, 18b Trumpington Road, Cambridge CB2 8AH, UK. e-mail: [email protected] 173 al questionnd DSM-IV entify subtle 5 www.sagepublications.com DOI: 10.1177/1362361307075710 aut.sagepub.co Downloaded from manifestations of autism spectrum conditions, and in particular Asperger syndrome. The questionnaire includes 31 key items contributing to a child’s total score, along with six control questions on general development. The CAST has been used in population-based epidemiological research as a screen for autism spectrum conditions in primary school aged children, and previous studies have shown reasonable sensitivity and specificity when using a screening cut-point of ≥15 (Scott et al., 2002). In this pilot study, all the children with a diagnosis of Asperger syndrome scored at 15 or above while none of the typically developing children scored above 15. The CAST has good validity (see Williams et al., 2005), and it is also important to assess its reliability and stability over time. Test–retest reliability of the CAST was investigated in a previous study (Williams et al., 2006). The aim of that study was to examine the test–retest reliability in a population sample according to the score categories currently used for sampling in research, and also treating the CAST as a scale. The CAST showed good agreement between screen results at or above, and below, a cut-point of 15 with a kappa statistic of 0.70. This study was based on a sample from mainstream schools, and therefore only a small proportion of children scored above the cut-point on the CAST. An important aspect of test–retest reliability of a screening instrument is to establish the stability of the screen near the proposed cut-point. A comparison between test– retest reliability in published autism screening tests has been reviewed elsewhere (Williams et al., 2006). The aim of the present study is to examine the test–retest reliability of the CAST in a sample enriched by children scoring at or above the cut-point of 15, as well as a proportion of those scoring 12–14.