Person ability scores as an alternative to norm-referenced scores as outcome measures in studies of neurodevelopmental disorders

Cristan A. Farmer*, Aaron J. Kaat, Audrey Thurm, Irina Anselm, Natacha Akshoomoff, Amanda Bennett, Leandra Berry, Aleksandra Bruchey, Bruce A. Barshop, Elizabeth Berry-Kravis, Simona Bianconi, Kim M. Cecil, Robert J. Davis, Can Ficicioglu, Forbes D. Porter, Allison Wainer, Robin P. Goin-Kochel, Caroline Leonczyk, Whitney Guthrie, Dwight KoeberlJamie Love-Nichols, Eva Mamak, Saadet Mercimek Andrews, Rebecca P. Thomas, Gail A. Spiridigliozzi, Nancy Sullivan, Vernon R. Sutton, Manisha D. Udhnani, Susan E. Waisbren, Judith S. Miller

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

4 Scopus citations


Although norm-referenced scores are essential to the identification of disability, they possess several features which affect their sensitivity to change. Norm-referenced scores often decrease over time among people with neurodevelopmental disorders who exhibit slower-than-average increases in ability. Further, the reliability of norm-referenced scores is lower at the tails of the distribution, resulting in floor effects and increased measurement error for people with neurodevelopmental disorders. In contrast, the person ability scores generated during the process of constructing a standardized test with item response theory are designed to assess change. We illustrate these limitations of norm-referenced scores, and relative advantages of ability scores, using data from studies of autism spectrum disorder and creatine transporter deficiency.

Original languageEnglish (US)
Pages (from-to)475-480
Number of pages6
JournalAmerican Journal on Intellectual and Developmental Disabilities
Issue number6
StatePublished - Nov 2020


  • Ability score
  • Floor effect
  • Item response theory
  • Neurodevelopmental disorder
  • Outcome measures

ASJC Scopus subject areas

  • Pediatrics, Perinatology, and Child Health
  • Neuropsychology and Physiological Psychology
  • Developmental and Educational Psychology
  • Arts and Humanities (miscellaneous)
  • Clinical Neurology
  • Psychiatry and Mental health


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