The Composition of Normative Groups and Diagnostic Decision Making: Shooting Ourselves in the Foot Purpose The normative group of a norm-referenced test is intended to provide a basis for interpreting test scores. However, the composition of the normative group may facilitate or impede different types of diagnostic interpretations. This article considers who should be included in a normative sample and how this decision must ... Research Article
Research Article  |   August 01, 2006
The Composition of Normative Groups and Diagnostic Decision Making: Shooting Ourselves in the Foot
 
Author Affiliations & Notes
  • Elizabeth D. Peña
    The University of Texas at Austin
  • Tammie J. Spaulding
    University of Arizona, Tucson
  • Elena Plante
    University of Arizona, Tucson
  • Contact author: Elizabeth Peña, 2504-A Whitis, Room 7.214, University of Texas at Austin, Austin, TX 78712. E-mail: lizp@mail.utexas.edu
Article Information
Language Disorders / Attention, Memory & Executive Functions / Research Articles
Research Article   |   August 01, 2006
The Composition of Normative Groups and Diagnostic Decision Making: Shooting Ourselves in the Foot
American Journal of Speech-Language Pathology, August 2006, Vol. 15, 247-254. doi:10.1044/1058-0360(2006/023)
History: Received April 11, 2005 , Revised July 20, 2005 , Accepted February 20, 2006
 
American Journal of Speech-Language Pathology, August 2006, Vol. 15, 247-254. doi:10.1044/1058-0360(2006/023)
History: Received April 11, 2005; Revised July 20, 2005; Accepted February 20, 2006
Web of Science® Times Cited: 37

Purpose The normative group of a norm-referenced test is intended to provide a basis for interpreting test scores. However, the composition of the normative group may facilitate or impede different types of diagnostic interpretations. This article considers who should be included in a normative sample and how this decision must be made relative to the purpose for which a test is intended.

Method The way in which the composition of the normative sample affects classification accuracy is demonstrated through a test review followed by a simulation study. The test review examined the descriptions of the normative group in a sample of 32 child language tests. The mean performance reported in the test manual for the sample of language impaired children was compared with the sample’s norms, which either included or excluded children with language impairment. For the simulation, 2 contrasting normative procedures were modeled. The first procedure included a mixed group of representative cases (language impaired and normal cases). The second procedure excluded the language impaired cases from the norm.

Results Both the data obtained from test manuals and the data simulation based on population characteristics supported our claim that use of mixed normative groups decreases the ability to accurately identify language impairment. Tests that used mixed norms had smaller differences between the normative and language impaired groups in comparison with tests that excluded children with impairment within the normative sample. The simulation demonstrated mixed norms that lowered the group mean and increased the standard deviation, resulting in decreased classification accuracy.

Conclusions When the purpose of testing is to identify children with impaired language skills, including children with language impairment in the normative sample can reduce identification accuracy.

Acknowledgments
Funding was provided to the second author by the Bamford-Lahey Children’s Foundation. The authors would like to thank Lynn Gale, PhD, for the production of Figures 2 and 3. This work was completed while the first author was a Fellow at the Center for Advanced Study in the Behavioral Sciences.
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