Detecting Incomplete Effort with Digit Span from the Wechsler Adult Intelligence Scale—Third Edition

Abstract

The current study evaluated the utility of the Digit Span subtest in discriminating patients with mild head trauma from individuals referred for independent neuropsychological evaluation with objective evidence of poor effort. Various indices from the Digit Span subtest were evaluated to determine the best discriminator of brain injury from poor motivation patient groups: Digit Span Forward, Digit Span Backwards, Reliable Digit Span, Digit Span Age-Corrected Scaled Score, and the difference score between the Vocabulary and Digit Span scaled scores. The Digit Span scaled score was found to be the best discriminating index. A cutoff score of less than or equal to 7 accurately classified 75% of persons in the incomplete effort group and 69% of persons in the TBI group. Application of this cutoff score to a non-litigating mild brain injury group yielded a 77% correct classification rate. However, Digit Span scaled score accounted for a modest amount of variation and it is not recommended as a stand-alone validity measure.

Notes

Notes. TBI = traumatic brain injury; PM = probable malingering; MTBI = nonlitigating mild traumatic brain injury.

^a TBI group is significantly different than other two groups.

^b All three groups differ significantly from each other.

^c Mild TBI significantly different from the other two groups.

^d PM significantly different from the other two groups.

Notes. C.I. = confidence interval.

+LR = positive likelihood ratio.

−LR = negative likelihood ratio.