Suspiciously slow: timed digit span as an embedded performance validity measure in a sample of veterans with mTBI

To explore the utility of Timed Digit Span (TDS) as an embedded performance validity test (PVT) in a sample of veterans with mild traumatic brain injury (mTBI). We hypothesize that TDS will predict PVT failure on an established stand-alone measure (Trial 1 of the Test of Memory Malingering; TOMM).

TDS was compared to Digit Span accuracy (DS), using TOMM as a criterion measure, in a sample of 99 veterans with mTBI. Correlation and regression were used to characterize associations between PVTs. Logistic regression was utilized to examine the relationship between embedded PVTs and the odds of TOMM failure. Classification accuracy of TDS was examined using receiver operating characteristic (ROC) curves. Predictive power of TDS to estimate TOMM failure was calculated for the current sample and for hypothetical populations with common base rates (BRs).

TDS significantly predicted failure on the TOMM and added greater incremental predictive value to the model compared to DS accuracy. Estimates of the predictive power of TDS were calculated using observed and hypothetical BRs. Sensitivity to stand-alone PVT, failure was 38% when specificity was set at 90%.

TDS offers a promising embedded PVT method, given its strong convergence with an established stand-alone PVT.