title: Developmental differences in intra-individual variability in children with ADHD and ASD.
abstract: BACKGROUND
  Intra-individual variability reflects temporal variation within an individual's performance on a cognitive task. Children with developmental disorders, such as ADHD and ASD show increased levels of intra-individual variability. In typical development, intra-individual variability decreases sharply between the ages 6 and 20. The tight link between intra-individual variability and age has led to the suggestion that it may be marker of neural development. As there is accumulating evidence that ADHD and ASD are characterised by atypical neurodevelopmental trajectories, we set out to explore developmental changes in intra-individual variability in subjects with ADHD and ASD.
  
  
  METHODS
  We used propensity score matching to match a cross-sectional sample of children with ADHD, ASD and control subjects (N = 405, aged 6-19 years old) for age, IQ and gender. We used ex-Gaussian distribution parameters to characterise intra-individual variability on fast responses (sigma) and slow responses (tau).
  
  
  RESULTS
  Results showed that there was a similar decrease in mean response times with age across groups, and an interaction between age and group for measures of variability, where there was a much lower rate of change in the variability parameters (sigma and tau) for subjects with ASD compared with the other two groups. Subjects with ADHD had higher intra-individual variability, reflected by both sigma and tau, but the rate of decrease in variability with age was similar to that of the controls.
  
  
  CONCLUSIONS
  These results suggest that subjects with ADHD, ASD and controls differ in the rate at which intra-individual variability decreases during development, and support the idea that intra-individual variability may be a marker of neural development, mimicking the neurodevelopmental changes in these disorders.
authors: NICHE Lab, Department of Psychiatry, Rudolf Magnus Magnus Brain Centre, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors: Janna
authors: J
authors: van Belle
authors: NICHE Lab, Department of Psychiatry, Rudolf Magnus Magnus Brain Centre, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors: Branko M
authors: BM
authors: van Hulst
authors: NICHE Lab, Department of Psychiatry, Rudolf Magnus Magnus Brain Centre, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors: Sarah
authors: S
authors: Durston
mesh_terms: D000293:Adolescent; D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000503:physiopathology*; D000067877:Autism Spectrum Disorder / Q000503:physiopathology*; D002648:Child; D003430:Cross-Sectional Studies; D006803:Human Development / Q000502:physiology*; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests / Q000706:statistics & numerical data*; D011597:Psychomotor Performance / Q000502:physiology*; D055815:Young Adult
keywords: ADHD; ASD; Development; ex-Gaussian distribution; intra individual response variability