A psychometric assessment of Wechsler short forms and the Shipley Institute of Living Scale in the estimation of Wechsler Adult Intelligence Scale-III IQ scores with an aging sample
Short forms of extensive assessment batteries are desired by clinicians in order to reduce testing time, as well as to reduce the fatigue and frustration that examinees may encounter during a long testing session. Four short-forms commonly associated with the WAIS-R and two conversion formulae commonly used with the Shipley Institute of Living Scale (SILS) were evaluated on their accuracy in estimating full-scale WAIS-III IQ scores on various criteria with a sample of elderly participants. All of the estimation procedures produced mean estimates of Full-Scale IQ (FSIQ) that were comparable to the full-form FSIQ, and all evidenced highly significant correlations with FSIQ. Consistent with previous literature, qualitative classification rates were not very high, compromising the utility of all of the short forms to some degree. When considering non-psychometric factors (e.g., testing time, ease of administration and scoring) and psychometric factors (e.g., reliability, validity), a 4-subtest short form by Silverstein (1982) emerged as the most psychometrically valid, and also as the most clinically useful short form. A 4-subtest short form by Ward et al. (1987) was comparable, but evidenced poor validity. The SILS, while providing accurate mean estimates, was not as highly correlated with FSIQ, produced many estimation and classification errors, and was found to be difficult by many participants. All of the Wechsler-based short forms could mimic the full-form in mapping cognition over the elderly lifespan, but the SILS deviated to a large degree. Trend analysis of the data did not find the linear decrease in cognition that is commonly found in cross-sectional studies with the elderly (Botwinick, 1977). Future research i short forms for the WAIS-III need to be carried out, especially with regards to improving classification accuracy. Specific questions regarding the WAIS-III and the elderly also need to be addressed (e.g., item difficulty).