Geographic distribution of ID prevalence relative to the birth cohort n=11,034 and ID n=916: Unadjusted (A) and fully adjusted models (B) are presented using the optimal span size of each (0.10 and 0.30 respectively). The unadjusted model is significantly different than flat (global P<0.001). Areas of significantly increased and decreased risk are indicated by black contour bands. Adjusted model is not significantly different than flat (global P=0.065). Adjustment factors were year of birth; plurality; maternal age, race, and level of education; and report of tobacco use during pregnancy.