Urban–Rural Differences and Sex-Specific Cognitive Effects on Autism Symptom Trajectories: A Longitudinal Study of Autistic Children in Taiwan

Few longitudinal studies have mapped autism symptom trajectories outside Western contexts. This study aimed to characterize trajectories of autism symptoms, assessed using the Autism Diagnostic Observation Schedule (ADOS), and associated child and family factors among autistic children from two regions in Taiwan that differ by urbanicity. Another aim was to examine the time-varying effects of children's cognitive abilities on autism symptoms, which remain understudied due to prior reliance on baseline proxies. Children with a confirmed autism diagnosis (n = 180, 87.8% male) were followed across three waves of data collection from ages 2 to 11 years. Linear multilevel growth models with random intercepts and slopes were used to estimate symptom trajectories at the total and domain levels of the ADOS. On average, total and social-affect symptoms increased significantly with age, while restricted and repetitive behaviors (RRBs) remained stable. Children from urban areas showed higher baseline RRBs and smaller increases in social-affect symptoms compared to those from rural areas. Additionally, children diagnosed under DSM-5 criteria showed lower baseline symptoms but greater increases in total/social-affect symptoms over time than their DSM-IV counterparts. A sex interaction effect was observed in the time-varying associations between IQ (particularly verbal IQ) and total/social-affect symptoms, with girls showing stronger negative IQ-symptom associations. These findings highlight the developmental complexity underlying the manifestation of autism symptoms, particularly at the intersection of sex and cognition. The distinct patterns by urbanicity also underscore the need to mitigate urban–rural disparities in service access to better support autistic children's long-term outcomes.