The new research, which mirrored the methods of the previous study in order to make as accurate a comparison as possible of the two years, has been published online in the journal Autism.

The study finds that ASD prevalence rose over the four year period both for boys (from 17.0 to 28.7 per thousand) and for girls (from 4.1 to 5.9 per thousand). ASD prevalence also varied by ethnicity, with white non-Hispanic children showing the highest levels of ASD, 20.4 per thousand in 2006 compared with 15.0 per thousand for black, non-Hispanic; 14.7 per thousand for Hispanic; and 14.0 per thousand among Asian children.

Zahorodny, who is an assistant professor of pediatrics and psychiatry at UMDNJ-New Jersey Medical School, says the rises in ASD prevalence that the new study documents fall in line with those measured when similar methodology has been applied in other states. That, in turn, indicates that children in New Jersey do not appear more at risk for ASD than others, as some had earlier feared. "New Jersey has long been a leading indicator of general ASD prevalence, because our state was out front early in its ability to recognize and symptoms in schools and health care settings," says Zahorodny. "As diagnostic skills become more sophisticated in other states, we are finding that they, too, are seeing higher numbers."

They are numbers that exceed experts' earlier expectations. "In various parts of the United States, overall ASD prevalence is approaching two percent," Zahorodny says. "In the past, scientists predicted the prevalence rates would ultimately level off around one percent." Zahorodny says further research is needed to determine what factors have contributed to rises in documented cases of ASD, and also whether documented ASD prevalence will now plateau at approximately two percent or continue to rise when later years are thoroughly analyzed.

About UMDNJ: The University of Medicine and Dentistry of New Jersey (UMDNJ) is New Jersey's only health sciences university with more than 6,000 students on five campuses attending three medical schools, the State's only dental school, a graduate school of biomedical sciences, a school of health related professions, a school of nursing and New Jersey's only school of public health. UMDNJ operates University Hospital, a Level I Trauma Center in Newark, and University Behavioral HealthCare, which provides a continuum of healthcare services with multiple locations throughout the State.