Nearly two-thirds of the increase of autism in Danish children is due to new diagnostic procedures, testing, and tracking methods. A new study in the medical journal JAMA Pediatrics found that the rising autism rates can be traced to identifying previously undiagnosed people with autism, rather than an increase in the disorder itself. In other words, the Danish did a better job of finding who is autistic. Researchers examined more than half a million children’s health records to reach their conclusion, amid years of speculation over causation. There are no comparative studies yet to prove this theory works in the U.S. “No one has offered a convincing explanation for why an increase is occurring, if it is,” says Glen Elliott, medical director of Children’s Health Council in California.