The debate has simmered over the past year as an expert panel appointed by the American Psychiatric Association has updated its proposals for the association’s Diagnostic and Statistical Manual of Mental Disorders, scheduled to take effect in May 2013. The manual is the field’s standard reference, and several recent studies suggested that the amended autism definition was far narrower than intended.

“What I would say to families worried about the new criteria is that they’re more open-ended than the old ones,” said Catherine Lord, the senior researcher on the study. “So it’s very important to find a clinician who understands them, and who is not rushed when making a diagnosis.”

The new analysis, the largest to date, is effectively an answer to previous studies that had forecast many more children would not meet the new definition. Dr. Lord serves on the panel that proposed the new definition.

“Everyone has been waiting to see what the impact of the new diagnosis is going to be, and this study is the most comprehensive we have to date,” said Sally Ozonoff, vice chairwoman for research in the department of psychiatry and behavioral sciences at the University of California, Davis, MIND Institute. Dr. Ozonoff was not involved in the research or the debate over its implications.

In the study, Dr. Lord’s team analyzed case files for children who received an autism diagnosis under the current criteria, exhibiting six or more of 12 behaviors, like language delays and absence of social bonding or eye contact. The team asked which of these youngsters would qualify under the proposed definition, which requires just three deficits in social interaction and at least two in “repetitive behaviors,” a category that includes hypersensitivities and fixations.