Effort has a greater effect on test scores than severe brain injury in compensation claimants

TLDR

The study assessed 904 consecutive patients—80 neurological and 470 head‑injury cases—using a battery of 43 neuropsychological tests, converting each score to a normative Z‑score and averaging them to produce an Overall Test Battery Mean (OTBM). Effort strongly correlated with overall test performance (r = 0.73), and sub‑optimal effort suppressed the OTBM 4.5 times more than moderate‑severe brain injury; when only good‑effort cases were considered, severe brain‑injury and neurological patients scored significantly lower than presumed healthy controls, highlighting the need to assess effort in neuropsychological evaluations.

Abstract

Nine-hundred and four consecutive patients, including 80 neurological patients and 470 with head injuries, were given neuropsychological tests. All 43 test scores were converted to normative Z-scores and averaged, giving an Overall Test Battery Mean (OTBM). A variable measuring effort correlated 0.73 with the OTBM. The OTBM mean score was 1.20 SD lower in those who failed the Word Memory Test (WMT) than in those who passed the WMT. Sub-optimal effort suppressed the OTBM 4.5 times more than did moderate-severe brain injury. When only those making a good effort were included, patients with severe brain injuries and neurological diseases scored significantly lower than groups presumed to have no neurological impairment, but these group differences were not seen when all cases were analysed together. These data illustrate the importance of measuring and controlling for sub-optimal effort in individual neuropsychological evaluations, as well as in empirical research with similar groups of patients.