Table 2.

Adjusted relative risk (RR) of a change in autism spectrum disorder (ASD) diagnosis

	RR	95% Confidence interval	p value
Female	0.88	0.76–1.01	.069
Mother’s highest level of education
≤High school diploma	1.00	-	-
Associate’s degree or some college	1.02	0.86–1.22	.807
≥Bachelor’s degree	0.99	0.84–1.18	.943
Race
White	1.00	-	-
African American	1.01	0.75–1.35	.944
Multiple	1.00	0.75–1.35	.955
Other	0.88	0.68–1.13	.313
US region
Northeast	1.00	-	-
Midwest	1.15	0.99–1.34	.076
South	1.29	1.13–1.48	<.001
West	1.26	1.07–1.49	.007
Era of initial diagnosis
After 2001	1.00	-	-
1995–2001	0.71	0.62–0.81	<.001
Before 1995	0.68	0.51–0.89	.005
Initial ASD diagnosisa
AD	1.00	-	-
AS	1.34	1.04–1.74	.026
PDD-NOS	5.65	4.86–6.57	<.001
‘PDD’/‘ASD’	4.63	3.88–5.52	<.001
Age of initial diagnosis
Under 4 years	1.00	-	-
4—8 years	0.92	0.82–1.03	.133
Over 8 years	1.00	0.78–1.27	.989
Clinician(s) assigning initial diagnosis
Team of health professionals	1.00	-	-
Pediatrician	1.73	1.31–2.29	<.001
Developmental pediatrician	1.39	1.13–1.69	.001
Psychiatrist	1.67	1.33–2.11	<.001
Clinical psychologist	1.38	1.11–1.69	.003
Neurologist	1.47	1.21–1.80	<.001
Team of professionals in a school system	1.32	1.01–1.72	.040
Speech and language pathologist	1.55	1.07–2.04	.020
Other	1.47	1.11–1.95	.008
Location of initial diagnosis
Healthy system	1.00	-	-
School system	1.24	1.00–1.55	.052
Early intervention	1.11	0.95–1.30	.181
Other	1.02	0.86–1.20	.833
History of autistic regression	1.15	1.02–1.29	.022

^aAD = autism or autistic disorder; AS = Asperger’s syndrome; PDD-NOS = pervasive developmental disorder—not otherwise specified; ‘PDD’ = pervasive developmental disorder; ‘ASD’ = autism spectrum disorder