This study was designed to examine the classification accuracy of the Erdodi
Index (EI-5), a novel method for aggregating validity indicators that takes into
account both thenumberandextentof
performance validity test (PVT) failures. Archival data were collected from a
mixed clinical/forensic sample of 452 adults referred for neuropsychological
assessment. The classification accuracy of the EI-5 was evaluated against
established free-standing PVTs. The EI-5 achieved a good combination of
sensitivity (.65) and specificity (.97), correctly classifying 92% of the
sample. Its classification accuracy was comparable with that of another
free-standing PVT. Anindeterminaterange betweenPassandFailemerged as a legitimate
third outcome of performance validity assessment, indicating that the underlying
construct is an inherently continuous variable. Results support the use of the
EI model as a practical and psychometrically sound method of aggregating
multiple embedded PVTs into a single-number summary of performance validity.
Combining free-standing PVTs with the EI-5 resulted in a better separation
between credible and non-credible profiles, demonstrating incremental validity.
Findings are consistent with recent endorsements of a three-way outcome for PVTs
(Pass,Borderline, andFail).