Abstract
Regional fluctuations in cognitive ability have been reported worldwide. Given perennial concerns that the outcome of performance validity tests (PVTs) may be contaminated by genuine neuropsychological deficits, geographic differences may represent a confounding factor in determining the credibility of a given neurocognitive profile. This pilot study was designed to investigate whether geographic location affects base rates of failure (BRFail) on PVTs. BRFail were compared across a number of free-standing and embedded PVTs in patients with mild traumatic brain injury (mTBI) from two regions of the US (Midwest and New England). Retrospective archival data were collected from clinically referred patients with mTBI at two different academic medical centers (nMidwest = 76 and nNew England = 84). One free-standing PVT (Word Choice Test) and seven embedded PVTs were administered to both samples. The embedded validity indicators were combined into a single composite score using two different previously established aggregation methods. The New England sample obtained a higher score on the Verbal Comprehension Index of the WAIS-IV (d = .34, small-medium). The difference between the two regions in Full Scale IQ (FSIQ) was small (d = .28). When compared with the omnibus population mean (100), the effect of mTBI on FSIQ was small (d = .22) in the New England sample and medium (d = .53) in the Midwestern one. However, contrasts using estimates of regional FSIQ produced equivalent effect sizes (d: .47–.53). BRFail was similar on free-standing PVTs, but varied at random for embedded PVTs. Aggregating individual indices into a validity composite effectively neutralized regional variability in BRFail. Classification accuracy varied as a function of both geographic region and instruments. Despite small overall effect sizes, regional differences in cognitive ability may potentially influence clinical decision making, both in terms of diagnosis and performance validity assessment. There was an interaction between geographic region and instruments in terms of the internal consistency of PVT profiles. If replicated, the findings of this preliminary study have potentially important clinical, forensic, methodological, and epidemiological implications.