Table 4. Stratified Results: ASD and SESa Prevalence Ratios (95% CIb), Stratified by Gender, Pre-existing Diagnosis, Co-occurring Intellectual Disability, Developmental Regression, and Data Source.
| ASD Cases | Prevalence Ratios (95% CI) | ||||||
| N (%) | Living in a Poverty Areac (%) | Low SES | Medium SES | High SES | p-value χ2 | ||
| Total | 3680 (100) | 16.8 | 0.70 (0.64, 0.76) | Reference | 1.25 (1.16, 1.35) | <0.0001 | |
| Gender | Boys | 2994 (81.4) | 16.3 | 0.67 (0.60, 0.74) | Reference | 1.23 (1.13, 1.34) | <0.0001 |
| Girls | 686 (18.6) | 19.0 | 0.82 (0.67, 1.01) | Reference | 1.32 (1.11, 1.57) | <0.0001 | |
| Pre-existing ASD Diagnosis | None | 1244 (33.8) | 19.1 | 0.78 (0.67, 0.90) | Reference | 1.09 (0.94, 1.22) | <0.0001d |
| ASD (all) | 2436 (66.2) | 15.7 | 0.65 (0.58, 0.73) | Reference | 1.35 (1.23, 1.48) | <0.0001 | |
| Autistic Disorder | 1411 (38.3) | 17.8 | 0.73 (0.63, 0.84) | Reference | 1.24 (1.10, 1.40) | <0.0001 | |
| ASD Unspecified | 1025 (27.9) | 12.8 | 0.54 (0.45, 0.65) | Reference | 1.51 (1.31, 1.73) | <0.0001 | |
| Co-occurring Intellectual Disability | Present | 1179 (32.0) | 22.8 | 0.86 (0.75, 1.00) | Reference | 0.93 (0.81, 1.07) | 0.1262 |
| Absent | 1568 (42.6) | 14.0 | 0.52 (0.45, 0.61) | Reference | 1.39 (1.25, 1.55) | <0.0001 | |
| Unknown | 933 (25.4) | 17.6 | 0.76 (0.64, 0.92) | Reference | 1.47 (0.27, 1.71) | <0.0001 | |
| Developmental Regression | Present | 677 (18.4) | 16.4 | 0.67 (0.54, 0.82) | Reference | 1.22 (1.03, 1.45) | <0.0001 |
| Absent or unknown | 3003 (81.6) | 16.9 | 0.70 (0.64, 0.77) | Reference | 1.26 (1.16, 1.36) | <0.0001 | |
| Source Accesse | Health & School | 1652 (60.9) | 15.9 | 0.65 (0.55, 0.76) | Reference | 1.30 (1.14, 1.48) | <0.0001 |
| Health Only | 426 (15.7) | 15.1 | 0.88 (0.67, 1.14) | Reference | 1.21 (0.95, 1.54) | <0.0001 | |
| School Only | 635 (23.4) | 16.0 | 0.75 (0.64, 0.87) | Reference | 1.33 (1.17, 1.52) | <0.0001 | |
SES indicator is % above poverty level based on United States Census 2000 block group data.
CI = Confidence Interval.
Poverty areas include United States Census 2000 block groups in which more than 20% of families with children have incomes below the poverty level [38]. Percent of cases living in poverty is 20.4% in sites accessing only data from healthcare sources.
In addition to the χ2 test of the SES gradient within the stratum of children with no pre-existing ASD diagnosis, a separate χ2 test of the difference in the SES gradient for children with and without a pre-existing ASD diagnosis also resulted in a p-value <0.0001.
Restricted to sites with access to school records (n = 2713), including those in Arkansas, Arizona, Colorado, Georgia, Maryland, North Carolina, New Jersey, South Carolina.