Validity Testing in Dually Diagnosed Post-Traumatic Stress Disorder and Mild Closed Head Injury

Abstract

Prospects for the coexistence of post-traumatic stress syndrome (PTSS) and mild traumatic brain injury (mTBI) rely exclusively on subjective evidence, increasing the risk of response bias in a compensatable social context. Using a priori specificities derived from genuine brain disorder groups, we examined validity failure rates in three domains (symptom, cognitive, motor) in 799 persons reporting persistent subjective disability long after mild neurological injury. Validity tests included the Test of Memory Malingering, MMPI-2 Fake Bad Scale, and Infrequency (F) scales, reliable digit span, and Halstead-Reitan finger tapping. Analyses showed invalidity signs in large excess of actuarial expectations, with rising invalidity risk conditional on post-traumatic complexity; the highest failure rates were produced by the 95 persons reporting both neurogenic amnesia and re-experiencing symptoms. We propose an “over-endorsement continuum” hypothesis: The more complex the post-traumatic presentation after mild neurological injury, the stronger the association with response bias. Late-appearing dual diagnosis is a litigation phenomenon so intertwined with secondary gain as to be a byproduct of it.

Keywords:

• Dual diagnosis
• Late post-concussion syndrome
• Malingering
• Mild traumatic brain injury
• Noncredible scores
• Post-traumatic stress disorder
• Validity testing

Notes

Finger-tapping and strength scores represent the sum of average performances from both hands. PTA = post-traumatic amnesia. TBI = traumatic brain injury. TOMM = Test of Memory Malingering. MMPI-2 = Minnesota Multiphasic Personality Inventory, 2nd Edition.

N = Number of observations in a sample of 95. Probable Rule = < 10th percentile of cerebral disorder referent groups; Definite Rule = 1st percentile of cerebral disorder referent group; LR = Positive likelihood ratio and CI = 95 confidence intervals measured against cerebral disorder referent group; GRIPSUM = Sum of right and left hand peak grip strength with Smedley Dynamometer; MMPI-2 F = Infrequency scale; MMPI-2 FBS = Lees-Haley's Fake Bad Scale; SVT = Symptom validity test; TAPTOTAL = sum right and left hand average tapping scores; TOMM = Test of Memory Malingering; RDS = Reliable Digit Span.

Effect size and r determined by probit method for dichotomous data (Lipsey & Wilson, 2001). Cluster B = DSM-IV re-experiencing criteria for post-traumatic stress disorder. N = Number of observations in sample of 228 without re-experiencing symptoms and 95 with that symptom. SVT = Symptomvalidity test.

Effect size and r determined by probit method for dichotomous data (Lipsey & Wilson, 2001). LPCS = Late post-concussion syndrome. PTSS = Post-traumatic syndrome with or without re-experiencing symptoms.

LPCS = Late post-concussion syndrome. Subsyndromal = post-traumatic syndrome without re-experiencing symptoms. Dual diagnosis = post-traumatic syndrome including re-experiencing symptoms. Probable = performance at or worse than the 10th percentile of a genuine brain disorder group. Cognitive sign = any failure on reliable digit span, TOMM second trial or TOMM retention trial. Symptom sign = any excessive score on the MMPI-FBS or MMPI-F scale. Motor sign = any failure on finger tapping or grip strength.

*The summed probabilities of one, two, and three signs do not equate to the “any combination” probability because of rounding error.