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Reliability and abnormality of scaled-score ranges
1Mental Retardation Research Center, Lanterman Developmental Center Research Group, School of Medicine, University of California, Los Angeles 91769.
Journal of Clinical Psychology
|November 1, 1989
Summary
Statistical significance and unusualness are distinct concepts when evaluating test score differences. This principle applies to scaled-score ranges, as demonstrated using the WISC-R.
Area of Science:
- Psychometrics
- Educational Psychology
- Neuropsychological Assessment
Background:
- Test score differences are common in psychological and educational assessments.
- Interpreting these differences requires distinguishing between statistical reliability and clinical abnormality.
- The scaled-score range is a frequently used index for subtest scatter analysis.
Purpose of the Study:
- To demonstrate that the distinction between reliability and abnormality applies to scaled-score ranges.
- To illustrate this principle using data from the WISC-R (Wechsler Intelligence Scale for Children-Revised).
Main Methods:
- Conceptual analysis of statistical significance versus unusualness in score differences.
- Application of this distinction to the scaled-score range metric.
- Empirical evaluation using WISC-R scaled-score data.
Main Results:
- The reliability (statistical significance) of a scaled-score range is independent of its abnormality (unusualness).
- A statistically significant range may not be unusual, and an unusual range may not be statistically significant.
- WISC-R data confirmed this divergence between reliability and abnormality for scaled-score ranges.
Conclusions:
- Clinicians must differentiate between statistical significance and unusualness when interpreting scaled-score ranges.
- Misinterpreting scaled-score ranges can lead to inaccurate conclusions about cognitive profiles.
- The evaluation of subtest scatter requires careful consideration of both reliability and abnormality.
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