Classification Accuracy of the Portland Digit Recognition Test in Traumatic Brain Injury: Results of a Known-Groups Analysis

Abstract

The present study used a known-groups design to examine the accuracy of the Portland Digit Recognition Test (PDRT) in the detection of malingering in traumatic brain injury (TBI). Data were derived from 262 TBI patients who were classified as not malingering, possibly malingering, and malingering based on the Slick, Sherman, and Iverson (1999) criteria. The original PDRT cutoffs detected between 20 and 50% of malingering TBI patients with a false positive error rate of 5% or less. When the false positive error rate was held at 5%, across all item sets, sensitivity was as high as 70%. The results show that the original PDRT cutoffs are conservative and that higher scores detect more MND patients without causing the false positive error rate to become unacceptably high. Clinical application and future research needs are discussed.

Acknowledgments

This project is but one small piece of a much larger data collection project. Our research assistants, including Jeffrey Love, Matthew Heinly, Bridget M. Doane, Kelly Curtis, and Adrianne Brennan, have been tireless and their efforts are much appreciated.

Notes

¹ F ratios for all variables are significant at alpha < .001.

^abc row means with the same letter are not significantly different from each other.

Note. No Inc = TBI no incentive; Inc Only = TBI incentive only; MND = malingered neurocognitive dysfunction; Not MND = all TBI not malingering; SUS = Suspect; Prob = probable MND; Def = definite MND; All MND = combined probable and definite MND; M/S = moderate or severe TBI.

Note. No Inc = TBI no incentive; Inc Only = TBI incentive only; MND = malingered neurocognitive dysfunction; Not MND = all TBI not malingering; SUS = Suspect; Prob = probable MND; Def = definite MND; All MND = combined probable and definite MND; M/S = moderate or severe TBI.

Note. No Inc = TBI no incentive; Inc Only = TBI incentive only; MND = malingered neurocognitive dysfunction; Not MND = all TBI not malingering; SUS = Suspect; Prob = probable MND; Def = definite MND; All MND = combined probable and definite MND; M/S = moderate or severe TBI.

Note. MND = malingered neurocognitive dysfunction; Inc = Incentive; Poss = possible; All MND = probable MND + definite MND.

Note. BR = hypothetical base rate; CI = confidence interval; FP rate = false positive error rate; Sens = sensitivity.