Transdiagnostic Examination of Interrelationships Between Anxiety, Insistence on Sameness and Compulsions.

Although insistence on sameness (IS) and compulsions occur across a wide range of neurodevelopmental (NDD) and neuropsychiatric (NPD) conditions, they are typically only examined within the confines of specific singular disorders. Indeed, while anxiety has been consistently linked to IS in autism and compulsions in obsessive-compulsive disorder (OCD), no empirical study has examined these associations in a sample spanning a range of NDD and NPD. Therefore, this study utilized a large sample of children and adolescents spanning several NDD and NPD to examine whether anxiety shows different patterns of association with IS or compulsions within and across diagnostic groups. The transdiagnostic sample encompassed youth (mean age = 10.36 [3.40]; N = 1852) diagnosed with autism (N = 387), attention-deficit hyperactivity disorder (ADHD; N = 931), internalizing disorders (N = 208), OCD/Tic disorder (N = 59) and oppositional defiant/conduct disorder (ODD/CD; N = 267). IS and compulsions were assessed using the Repetitive Behavior Scale-Revised, and anxiety using the Screen for Child Anxiety Related Disorders. Within-group comparisons revealed that, in the autism, ADHD, and OCD/Tic groups, anxiety showed a slightly stronger association with IS than compulsions although effect sizes indicated small to no effect (q < 0.24). Between-group comparisons showed that interrelationships between anxiety, IS, and compulsions did not differ across groups, except for the association between IS and compulsions, which was slightly weaker in the ADHD group compared to the autism (z = 4.20) and ODD/CD groups (z = 3.32). Findings affirm the transdiagnostic nature of IS and compulsions and suggest that anxiety plays a key role in these behaviors, irrespective of primary diagnosis.