Recently, the New York Times showered attention on a new study from the M.I.N.D. Institute at U.C. Davis, giving it front-page news play and devoting an editorial to hand-wringing over its findings. Numerous other publications accorded it prominent attention, too, and just this week Senator Barbara Boxer cited it while arguing for new federal initiatives on autism. ["Report to the Legislature on the Principal Findings from The Epidemiology of Autism in California," M.I.N.D. Institute, University of California - Davis, October 17, 2002] The study purports to show that the recent explosion in autism among school-aged children is caused at least in part by a real increase in juvenile autism, not by improved reporting and diagnosis. Unfortunately, this study doesn't even come close to justifying its conclusion.
Over the past decade, the number of students labeled as autistic, while still very small as a portion of all U.S. schoolchildren, has been growing at an alarming speed. Even after we control for overall growth in the total pupil population, the rate of autism diagnoses almost quintupled between 1992 and 2000. Naturally, experts are urgently trying to find out whether this represents a real epidemic of autism or just a change in diagnostic patterns.
This question has implications beyond autism itself. Student enrollment in special education has grown wildly over the past decade. As federal I.D.E.A. legislation comes up for renewal, the $64,000 question is whether this growth is occurring because there really are more disabled kids, or because schools are putting kids into special education for other reasons (e.g. to collect more state funding, to get troublemakers out of "regular" classes). Autism is only a tiny share of the total increase in special education, but if there are more autistic kids than there used to be, that would tend to support the public schools' general contention that there are more disabled kids than there used to be. That's probably why the media gave this study so much coverage.
The U.C. Davis study, which looked at autistic children in California, reaches its conclusion that there really are more autistic kids by considering and rejecting three alternative explanations: that the formal diagnostic criteria for autism have changed; that significant numbers of autistic children were formerly misdiagnosed as mentally retarded and are now correctly diagnosed with autism; and that more autistic children have moved into California from out of state. All three hypotheses are refuted by the data considered in the study, and there is no obvious reason to doubt that the study is correct in rejecting them.
But there is a major gap between the rejection of these three alternative hypotheses and the study's conclusion: "Without evidence for an artificial increase in autism cases, we conclude that some, if not all, of the observed increase represents a true increase in cases of autism." Are we truly "without evidence for an artificial increase" simply because we can show that diagnostic criteria, previous misdiagnosis of autism as mental retardation, and family mobility did not cause such an increase?
The study overlooks another obvious possibility: that kids who used to go entirely undiagnosed, or were diagnosed with other disorders such as emotional disturbance, may now be diagnosed with autism. This is the most plausible explanation for the explosive growth in autism diagnoses. No one doubts that public awareness of autism has grown. Also, the severe stigma that was once associated with autism which may have led many parents and doctors to resist this diagnosis, has receded. Moreover, the growth in autism has taken place almost entirely among high-functioning children, who are exactly those most likely to have gone undiagnosed before.
The authors did the public no service by spinning their findings as they did. Their study does appear to refute some possible explanations for the rise in autism; had they stuck to that, the study would have been beneficial. Instead, they opted for hype over scholarly rigor, and the media, including the front page of the Times, focused on the study's unproven claim that there's been real growth in autism. This has muddied the waters of public discourse rather than clearing them.
Greg Forster is senior research associate at the Manhattan Institute's Education Research Office.
"Report to the Legislature on the Principal Findings from The Epidemiology of Autism in California," M.I.N.D. Institute, University of California - Davis, October 17, 2002
"Increase in Autism Baffles Scientists," by Sandra Blakeslee, The New York Times, October 18, 2002 (abstract only; full article available for a fee)
"A Mysterious Upsurge in Autism," editorial, The New York Times, October 20, 2002
"Autism research urged," by Dorsey Griffith, The Sacramento Bee, October 31, 2002
