Socioeconomic Status and Air Pollution Linked to State Autism Rates

A new cross-sectional analysis published in *Psychological Reports* examined autism spectrum disorder (ASD) prevalence across all fifty U.S. states using 2017 data. Led by Stewart J. H. McCann, professor emeritus of psychology at Cape Breton University, the research evaluated fifteen potential state-level predictors—including socioeconomic status (SES), racial demographics, urbanization, maternal age, and microscopic air-particle concentrations—to determine which factors independently relate to ASD rates among adults aged 18-84.

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The investigators first calculated simple correlations between each variable and state ASD prevalence. After observing significant links for most factors, they applied statistical control to hold SES constant, isolating the unique contribution of the remaining variables. A final multivariate model incorporated SES together with the six variables that retained significance after control (racial makeup, average personality profile, urban population share, air pollution, prenatal-to-3 policies, and maternal age).

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When all variables were entered simultaneously, only SES and air-pollution levels remained statistically significant independent predictors. Together they explained 55.7 % of the variance in state autism rates. All other factors—such as healthcare provider density, education spending, and intelligence scores—lost predictive power once SES and pollution were accounted for. A supplementary analysis showed that state ADHD rates displayed the opposite pattern, underscoring the specificity of the autism findings.

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The authors stress that the cross-sectional design precludes causal inference; higher ASD diagnoses in wealthier states may reflect greater diagnostic access rather than a biological effect. Moreover, applying aggregate state data to individuals risks an ecological fallacy. Future work is recommended to explore parental age and to replicate findings at the individual level.

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• “Most of my research in the past 20 years has focused on the implications of the geographical dispersion of personality and other individual differences across the U.S. states,” — Stewart J. H. McCann

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• “I was surprised that the correlations of 14 of the 15 potential predictors with ASD, largely gleaned from previous research with individuals as the units of analysis, also replicated with states as the analytic units,” — Stewart J. H. McCann

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• “I also was surprised by the fact that only SES and air pollution ultimately showed any independent relation to state ASD prevalence rates.” — Stewart J. H. McCann

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• “The present study has two important limitations,” — Stewart J. H. McCann

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• “First, the cross-sectional nature of the research means that readers cannot draw inferences regarding cause and effect and that the results cannot serve as empirical support for any causal speculations that might pertain to the findings.” — Stewart J. H. McCann

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