IQ test selection could be life-or-death decision: WAIS v SB score differences in ID/MR sample

Interesting article "in press" in Intelligence that compares WAIS and Stanford Binet IQ scores (across different editions except the current SB5 and WAIS-IV) for adults with intellectual disability (ID/MR).  Although the mixing together of scores across different editions makes it impossible to make SB/WAIS-specific edition comparisons, the finding that the WAIS scores were, on the average (mean), almost 17 points higher may surprise many psychologists.  The authors discuss the real-life implications (i.e., Atkins ID death penalty decisions; eligibility for SS benefits, etc.) of different scores from different tests.  As outlined in a prior IAP AP101 special report, differences of this magnitude between different IQ tests should not be surprising. 

Silverman, W., Miezejeski, C., Ryan, R., Zigman, W., Krinsky-McHale & Urv, T. (in press).  tanford-Binet and WAIS IQ differences and their implications for adults with intellectual disability (aka mental retardation).  Intelligence.

Abstract

Stanford-Binet and Wechsler Adult Intelligence Scale (WAIS) IQs were compared for a group of 74 adults with intellectual disability (ID). In every case, WAIS Full Scale IQ was higher than the Stanford-Binet Composite IQ, with a mean difference of 16.7 points. These differences did not appear to be due to the lower minimum possible score for the Stanford-Binet. Additional comparisons with other measures suggested that the WAIS might systematically underestimate severity of intellectual impairment. Implications of these findings are discussed regarding determination of disability status, estimating prevalence of ID, assessing dementia and aging-related cognitive declines, and diagnosis of ID in forensic cases involving a possible death penalty.

A concluding comment from the authors

Nevertheless, psychologists cannot meet their ethical obligations in these cases without knowing which test provides the most valid estimate of true intelligence. The present data for individuals with relatively higher IQs, though sparse, indicate that differences between the Stanford-Binet and WAIS IQ tests can no longer be summarily dismissed as merely reflecting the scales' different floors. When test results are informing judgments of literal life and death, any suspected uncertainty regarding the validity of outcomes must be addressed aggressively.

Article Outline

1. Method
2. Results
3. Discussion

• 3.1. Disability determinations
• 3.2. Prevalence of ID
• 3.3. Declines with aging
• 3.4. Death penalty cases
• 3.5. Conclusion

Acknowledgements
References

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