Final, generalised mixed-effect model showing random effects for ASD score modelled against white matter residual and grey matter volumes.

Formula:

“∼” means modelled against, and “(1| factor)” means that a factor is included as a random effect.
A generalised mixed-effect model is run using normalised volumes of grey and white matter as explanatory variables together with age as a random effect. ASD score is set as the response variable. The final model is derived following an iterative model selection procedure that involves comparing successive models using Akaike’s Information Criterion (see Methods for detailed description of model selection procedure). ASD score refers to an aggregate score from the four Children’s Social and Behavioural Questionnaire (CSBQ) subscales, (1) social interest, (2) social understanding, (3) stereotypy and (4) resistance to change.
Abbreviations: WM, normalised WM volume; GM, normalised GM volume; US, unaffected siblings; WM:GM, WM by GM interaction; US: Age, unaffected sibling by Age interaction; ADHD:Age, ADHD by Age interaction.