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Autism Prevalence and Precipitation Rates in California, Oregon, and Washington Counties
Michael Waldman, PhD; Sean Nicholson, PhD; Nodir Adilov, PhD; John Williams, MD, MBA
Principales medidas de resultado
Objective: To investigate empirically the possibility of Main Outcome Measures: County-level autism preva-
an environmentaltrigger for autism among genetically vulnerable children that is positively associated with precipitation.
Design: We used regression analysis to investigate autism prevalence rates and counts first in relation to mean annual county-level precipitation and then to the amount of precipitation a birth cohort was exposed to when younger than 3 years, controlling for time trend, population size, percapita income, and demographic characteristics. In some models, we included county fixedeffects rather than a full set of covariates. Setting: Counties in California, Oregon, and Washington. Participants: Children born in California, Oregon, and Washington between 1987 and 1999.
lence rates and counts.
Results: County-level autism prevalence rates and counts among school-aged children werepositively associated with a county’s mean annual precipitation. Also, the amount of precipitation a birth cohort was exposed to when younger than 3 years was positively associated with subsequent autism prevalence rates and counts in Oregon counties and California counties with a regional developmental services center. Conclusions: These results are consistent with the existence of an environmentaltrigger for autism among genetically vulnerable children that is positively associated with precipitation. Further studies focused on establishing whether such a trigger exists and identifying the specific trigger are warranted.
Main Exposure: County-level precipitation.
Arch Pediatr Adolesc Med. 2008;162(11):1026-1034 be important. However, little is known about what thesetriggers might be. We explore the possibility of an environmental trigger for autism by empirically investigating the association between countylevel precipitation rates and the prevalence of autism. The US Department of Education collects autism prevalence data by state. According to the 2003 survey, the 5 states with the lowest autism prevalence for 6- to 10-year-olds were New Mexico,Mississippi, Colorado, Oklahoma, and Tennessee, whereas Minnesota, Oregon, Indiana, Maine, and Massachusetts had the highest autism prevalence for this age group.5 Similarly, in the recent CDC study of autism prevalence mentioned previously, the highest autism prevalence among the 14 states studied was found in New Jersey, the second–most-northern state in the study, whereas the lowest autism prevalence wasfound in Alabama, the most southern state in the study.1
Author Affiliations: Johnson Graduate School of Management (Dr Waldman) and Department of Policy Analysis and Management (Dr Nicholson), Cornell University, Ithaca, New York; Department of Economics, Indiana University–Purdue University, Fort Wayne (Dr Adilov); and Department of Child and Adolescent Psychiatry, TheChildren’s Hospital of Philadelphia, Philadelphia, Pennsylvania (Dr Williams).
HIRTY YEARS AGO, IT WAS EStimated that roughly 1 in 2500 children had autism; the most recent Centers for Disease Control and Prevention (CDC) study calculated prevalence at 1 in 150.1 Some of this increase is likely owing to more active case ascertainment and changes in diagnostic criteria, and as much as half ofthe prevalence variation between studies is owing to differences in methods and population characteristics.2,3 Nevertheless, the possibility of a true increase in prevalence cannot be excluded.4
For editorial comment see page 1095
Despite the increase in prevalence and the resulting increased attention paid to the condition, knowledge about what causes autism is limited. It is understood...