Fig. 4

a Individuals with ASD were grouped into three subgroups based on the DDI values. Advanced group had higher brain age compared with chronological age (DDI > = 1). Delayed group had lower brain age compared with chronological age (DDI < = − 1). Balanced group had similar brain age and chronological age (− 0.2 < DDI < 0.2). b ASD severity values for the three subgroups. c The effect size of group difference between Advanced and Delayed groups. The effect size is reported as common-language effect size (i.e., probability of having higher severity in the Delayed group), which is an appropriate choice for ordinal severity values. The effect size was calculated for varying number of people in each group (adjusting DDI threshold accordingly) to demonstrate the robustness of group difference to the DDI threshold. Regardless of the sample sizes, the inter-group difference was always significant (p < 0.05)