Bowden, shores, & Mathias (2006): failure to replicate or just failure to notice. Does effort still account for more variance in neuropsychological test scores than TBI severity?

Several studies have reported that traumatic brain injury (TBI) has a smaller effect on neuropsychological test scores, in contrast to the large effect of poor effort on test performance. Consequently, many authors have concluded that effort needs to be measured routinely and that it is necessary to control for poor effort when measuring the effects of brain disease or injury on performance. Recently, however, Bowden, Shores, and Mathias (2006) have challenged these notions. They argued that the Immediate Recognition subtest of the Word Memory Test (Green & Flaro, 2003), an effort measure, is another verbal memory test rather than a measure of cognitive effort. In this study we re-examine the data from Bowden et al. (2006) and Green, Rohling, Lees-Haley, and Allen (2001) to identify differences between the two studies that might account for their contradictory conclusions. In both sets of data, reanalysis showed that effort explains approximately five times more of the variance in composite neuropsychological test scores than TBI severity. Importantly, scores on the Word Memory Test-Immediate Recognition (WMT-IR) were not correlated with measures of TBI severity, and were not found to correlate with major variables known to be measuring ability (e.g., years of education). These findings challenge the conclusions offered by Bowden and colleagues (2006).