title: Stability of cognitive performance in children with mild intellectual disability.
abstract: OBJECTIVE
  Longitudinal studies that have examined cognitive performance in children with intellectual disability more than twice over the course of their development are scarce. We assessed population and individual stability of cognitive performance in a clinical sample of children with borderline to mild non-syndromic intellectual disability.
  
  
  METHODS
  Thirty-six children (28 males, eight females; age range 3-19y) with borderline to mild intellectual disability (Full-scale IQ [FSIQ] 50-85) of unknown origin were examined in a retrospective clinical case series using linear mixed models including at least three assessments with standardized intelligence tests.
  
  
  RESULTS
  Average cognitive performance remained remarkably stable over time (high population stability, drop of only 0.38 IQ points per year, standard error=0.39, p=0.325) whereas individual stability was at best moderate (intraclass correlation of 0.58), indicating that about 60% of the residual variation in FSIQ scores can be attributed to between-child variability. Neither sex nor socio-economic status had a statistically significant impact on FSIQ.
  
  
  CONCLUSIONS
  Although intellectual disability during childhood is a relatively stable phenomenon, individual stability of IQ is only moderate, likely to be caused by test-to-test reliability (e.g. level of child's cooperation, motivation, and attention). Therefore, clinical decisions and predictions should not rely on single IQ assessments, but should also consider adaptive functioning and previous developmental history.
authors.affiliation: Child Development Center, University Children's Hospital Zürich, Zürich, Switzerland; Children's Research Center, University Children's Hospital Zürich, Zürich, Switzerland.
authors.forename: Oskar G
authors.initials: OG
authors.lastname: Jenni
authors.forename: Sylvia
authors.initials: S
authors.lastname: Fintelmann
authors.forename: Jon
authors.initials: J
authors.lastname: Caflisch
authors.forename: Beatrice
authors.initials: B
authors.lastname: Latal
authors.forename: Valentin
authors.initials: V
authors.lastname: Rousson
authors.forename: Aziz
authors.initials: A
authors.lastname: Chaouch
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D018450:Disease Progression; D005260:Female; D006801:Humans; D008607:Intellectual Disability / Q000175:diagnosis*; D007360:Intelligence / Q000502:physiology*; D007361:Intelligence Tests; D008297:Male; D009483:Neuropsychological Tests; D011379:Prognosis; D012720:Severity of Illness Index; D014888:Wechsler Scales; D055815:Young Adult