Reply to Charman et al.'s Commentary on the Modified Checklist for Autism in Toddlers

We appreciate the thoughtful and important points raised by Charman et al. (2001) in their commentary on our paper, and would like to provide a few responses about these points. With regard to clinic versus population samples, we agree that it is most important to examine item and total scale characteristics separately for unscreened samples as well as for children referred for early intervention but not yet evaluated or diagnosed. We are continuing to recruit many more children from pediatric practices and expect to have a sufficient sample to analyze these groups separately. It seems unlikely that specific predictive items will turn out to be quite different for the two populations, since there is so much agreement between items found predictive on the CHAT, the M-CHAT, and in such studies as Lord’s (1995), but this is an empirical question to be answered by future screening studies. With regard to scale characteristics for the CHAT 9 items, we were indeed interested in the classificatory power of the 9 items as a set, since one screening criterion would be a certain number of failed items on the total scale; the discriminant analysis should generally give higher weights to the items that individually discriminate the two groups. In the M-CHAT 22, we had the CHAT “filler” items plus an additional one (Does your child walk?) and were interested in the classificatory power of these items as a total set. The question concerning the classificatory power of the CHAT’s two major risk factors, pretend play and protodeclarative pointing, was a very interesting one. Although Charman et al. are certainly right in suggesting that two questions alone would not be expected to provide a reliable screen, we did investigate the performance of these two items alone (Items 5 and 7) in our database, as they suggested. Results indicate the frequencies shown in Table I. Thus, the two items work about as well as could be expected for any set of two items. Failing both items detects 18 of the 39 children with autism, or 46% sensitivity (this number would be expected to drop when missed children are found on later follow-up). The question of whether to use a parent report only or a parent report along with health professional observation is extremely important. Parent report has the advantages of the extensive knowledge parents have of their children, their observation of their children in multiple settings, and the fact that parental concerns are often found to be justified (Glascoe, MacLean, & Stone, 1991). On the other hand, parental inexperience, cultural expectations or attitudes about reporting problems, and emotional bias (such as denial or overconcern) can distort reporting. The U.S. health care system lacks the home health visitor system enjoyed in the U.K. A health professional’s observation would therefore have to be done in the pediatrician’s office. This observation would have the advantage of a large base for normative comparison and a more objective attitude (although clinical impression formation in detecting developmental disorders has been found to be far from objective; Glascoe & Dworkin, 1993). On the other hand, pediatricians have been found to underdetect very significantly both cognitive and emotional/behavioral disorders in young children (Glascoe & Dworkin, 1993; Rapin, 1996); no doubt,