Does effort suppress cognition after traumatic brain injury? A re-examination of the evidence for the Word Memory Test

Green, Rohling, Lees-Haley, and Allen (2001) suggested that scores on a test of "effort,'' the Word Memory Test (WMT), explains more variance in outcome after brain injury than does injury severity. As a consequence, Green and colleagues recommend using the WMT to control for sub-optimal effort in neuropsychological evaluations and group research. We re-examine the evidence for their conclusions and argue that identifying a larger proportion of explained variance is not in itself evidence of validity unless the premise to be proven is already assumed, namely, that the test is a valid measure of effort. Instead, the crux of Green and colleagues claim for the validity of the WMT implies an interaction between effort and injury severity on outcome scores, although the specific interaction has not been tested in their previous research. We failed to find any evidence for this interaction in a sample of 100 Australian litigants. We conclude that our data do not support the view that effort, as measured by the WMT, interacts with injury severity to suppress cognition after brain injury.