WAIS-IV Index and Full Scale Intelligence Quotient Score Differences between Standard and Prorated Scoring Methods
Abstract
Standard scoring methods for the Wechsler Adult Intelligence Scale, Fourth Edition (WAIS-IV) require that all core subtests be used to compute index scores, yet it is possible to prorate certain indices using a reduced number of subtests. The purpose of this study is to explore differences in WAIS-IV Verbal Comprehension, Perceptual Reasoning, and Full Scale IQ Index scores as a result of using standard versus prorated scoring methods. Participants were 149 adults, ages 18 to 84 who were previously administered the WAIS-IV. Protocols were scored using standard scoring methods and then re-scored using each alternate proration combination for Verbal Comprehension, Perceptual Reasoning, and Full Scale IQ Indices. One-factor repeated measures ANOVAs and post-hoc paired t-tests revealed that any verbal subtest may be removed without significantly altering Verbal Comprehension Index scores. Block Design + Matrix Reasoning produced the most accurate Perceptual Reasoning Index score estimates. When verbal and perceptual tests were removed from Full Scale IQ calculations, Block Design + Visual Puzzles produced significantly lower Full Scale IQ Index scores, and any inclusion of Matrix Reasoning + Visual Puzzles (in isolation or in combination with any of the Verbal Comprehension Index proration options) produced significantly higher Full Scale IQ scores. Results of removing working memory and/or processing speed subtests indicated that omitting Digit Span alone and omitting Symbol Search alone were the only two proration options that did not artificially inflate Full Scale IQ Index score estimations. The risks of prorating scores at the expense of losing accuracy must be measured against the benefits gained by doing so, and which subtests to omit must be chosen judiciously. The results of this study provide clinicians with guidelines to use when attempting to obtain prorated scores that are not significantly different from standard index scores.References
Axelrod, B. N., Dingell, J. D., Ryan, J. J., & Ward, L. C. (2000). Estimation of Wechsler Adult Intelligence Scale-III index scores with the 7-subtest short form in a clinical sample. Assessment, 7(2), 157-161. doi: 10.1177/107319110000700207
Axelrod, B.N. & Ryan, J.J. (2000). Prorating Wechsler Adult Intelligence Scale-III summary scores. Journal of Clinical Psychology, 56(6), 807-811. doi: 10.1002/(SICI)1097-4679(200006)56:6
Axelrod, B.N., Ryan, J.J. & Ward, L.C. (2001). Evaluation of seven-subtest short forms of the Wechsler Adult Intelligence Scale-III in a referred sample. Archives of Clinical Neuropsychology, 16, 1-8. doi: 10.1016/S0887-6177(99)00054-2
Axelrod, B. N., Vanderploeg, R. D., & Schinka, J. A. (1999). Comparing methods for estimating premorbid intellectual functioning. Archives of Clinical Neuropsychology, 14(4), 341-346. doi:10.1016/S0887-6177(98)00028-6
Benson, N., Hulac, D.M., & Kranzler, J.H. (2010). Independent examination of the Wechsler Adult Intelligence Scale – Fourth Edition (WAIS-IV): What does the WAIS-IV measure? Psychological Assessment, 22(1), 121-130. doi: 10.1037/a0017767
Myers, J.L., Well, A.D., & Lorch, R.F. (2010). Research design and statistical analyses, third edition. New York: NY: Routledge.
Palmer, B.W., Taylor, M.J. & Heaton, R.K. (2003). Accuracy of WAIS-III – WMS-III joint factor scores when one or more subtests is omitted or an alternate subtest is employed. In D.S. Tulsky (Ed.), Clinical interpretation of the WAIS-III and WMS-III (pp.391-450).
Sattler, J.M. & Ryan, J.J. (2009). Assessment with the WAIS-IV. La Mesa, CA: Jerome M. Sattler, Publisher, Inc.
Umfleet, L.G., Ryan, J.J., Gontkovsky, S.T. & Morris, J. (2012). Estimating WAIS-IV indices: Proration versus linear scaling in a clinical sample. Journal of Clinical Psychology, 68(4), 390-396. doi: 10.1002/jclp.21827
Wechsler, D. (1944). The measurement of adult intelligence (3rd ed.). Baltimore, MD: The Williams and Wilkins Company.
Wechsler, D. (2008). Wechsler Adult Intelligence Scale (4th ed.). San Antonio, TX: The Psychological Corporation.
