A solution to limitations of cognitive testing in children with intellectual disabilities: The case of fragile X syndrome

David R Hessl, Danh V. Nguyen, Cherie Green, Alyssa Chavez, Flora Tassone, Randi J Hagerman, Damla Senturk, Andrea Schneider, Amy Lightbody, Allan L. Reiss, Scott Hall

Research output: Contribution to journalArticle

95 Citations (Scopus)

Abstract

Intelligence testing in children with intellectual disabilities (ID) has significant limitations. The normative samples of widely used intelligence tests, such as the Wechsler Intelligence Scales, rarely include an adequate number of subjects with ID needed to provide sensitive measurement in the very low ability range, and they are highly subject to floor effects. The IQ measurement problems in these children prevent characterization of strengths and weaknesses, poorer estimates of cognitive abilities in research applications, and in clinical settings, limited utility for assessment, prognosis estimation, and planning intervention. Here, we examined the sensitivity of the Wechsler Intelligence Scale for Children (WISC-III) in a large sample of children with fragile X syndrome (FXS), the most common cause of inherited ID. The WISC-III was administered to 217 children with FXS (age 6-17 years, 83 girls and 134 boys). Using raw norms data obtained with permission from the Psychological Corporation, we calculated normalized scores representing each participant's actual deviation from the standardization sample using a z-score transformation. To validate this approach, we compared correlations between the new normalized scores versus the usual standard scores with a measure of adaptive behavior (Vineland Adaptive Behavior Scales) and with a genetic measure specific to FXS (FMR1 protein or FMRP). The distribution of WISC-III standard scores showed significant skewing with floor effects in a high proportion of participants, especially males (64.9%-94.0% across subtests). With the z-score normalization, the flooring problems were eliminated and scores were normally distributed. Furthermore, we found correlations between cognitive performance and adaptive behavior, and between cognition and FMRP that were very much improved when using these normalized scores in contrast to the usual standardized scores. The results of this study show that meaningful variation in intellectual ability in children with FXS, and probably other populations of children with neurodevelopmental disorders, is obscured by the usual translation of raw scores into standardized scores. A method of raw score transformation may improve the characterization of cognitive functioning in ID populations, especially for research applications.

Original languageEnglish (US)
Pages (from-to)33-45
Number of pages13
JournalJournal of Neurodevelopmental Disorders
Volume1
Issue number1
DOIs
StatePublished - 2009

Fingerprint

Fragile X Syndrome
Disabled Children
Intellectual Disability
Aptitude
Psychological Adaptation
Intelligence
Wechsler Scales
Fragile X Mental Retardation Protein
Intelligence Tests
Research
Cognition
Population
Psychology

Keywords

  • Assessment
  • FMR1 gene
  • FMRP
  • IQ
  • Mental retardation

ASJC Scopus subject areas

  • Clinical Neurology
  • Pathology and Forensic Medicine
  • Cognitive Neuroscience
  • Pediatrics, Perinatology, and Child Health

Cite this

A solution to limitations of cognitive testing in children with intellectual disabilities : The case of fragile X syndrome. / Hessl, David R; Nguyen, Danh V.; Green, Cherie; Chavez, Alyssa; Tassone, Flora; Hagerman, Randi J; Senturk, Damla; Schneider, Andrea; Lightbody, Amy; Reiss, Allan L.; Hall, Scott.

In: Journal of Neurodevelopmental Disorders, Vol. 1, No. 1, 2009, p. 33-45.

Research output: Contribution to journalArticle

Hessl, David R ; Nguyen, Danh V. ; Green, Cherie ; Chavez, Alyssa ; Tassone, Flora ; Hagerman, Randi J ; Senturk, Damla ; Schneider, Andrea ; Lightbody, Amy ; Reiss, Allan L. ; Hall, Scott. / A solution to limitations of cognitive testing in children with intellectual disabilities : The case of fragile X syndrome. In: Journal of Neurodevelopmental Disorders. 2009 ; Vol. 1, No. 1. pp. 33-45.
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