Forensic Neuropsychology and the MMPI2: Discriminating Between Neurologic and Psychiatric Conditions

1
Forensic Neuropsychology and the MMPI-2
Discriminating Between Neurologic and
Psychiatric Conditions
Graeme J. Senior, Ph.D., University of Southern
Queensland, and Lucille A. Douglas, Ph.D.,
Assessment Services in Psychology
Nor is this high error rate restricted to the
more recent diagnostic groups as is illustrated
in Table 3 with the Depression and TBI groups.
Here again the misclassification rate has a mean
of 67 where 1 in every 3 cases was classified
incorrectly. The classification errors are even
larger when applying the common clinical
heuristic of T-scores greater than or equal to 65
indicating clinically significant elevations (see
Table 4). Table 4. Percentage of Cases with
Elevations on Special Scales
In addition to the Basic and Content Scales of
the MMPI-2 the following special scales and
subscales were also examined PK
(Post-Traumatic Stress Disorder-Keane). This
supplementary scale was developed specifically
for the evaluation of PTSD (Keane, Malloy,
Fairbank, 1984). TBIf (Traumatic Brain Injury
in a forensic setting). This scale was developed
specifically for the evaluation of traumatic
brain injury in the personal injury claimant
setting (Senior, Lothrop, Deacon, 1999). It has
three subscales evaluating cognitive (TBIf1)),
emotional (TBIf2)), and physical (TBIf3) aspects
of TBI. CII (Cerebral Impairment Index). This
scale was developed to assess self-reports of TBI
cases in clinical and rehabilitation settings
(Jacobucci, 1993). It has five subscales
evaluating Memory/Concentration (CII1),
Neurological Symptoms (CII2), Muscular Control
(CII3), Passivity/Apathy (CII4), and
Anger/Impulsivity (CII5).
The Minnesota Multiphasic Personality Inventory
(MMPI) was originally developed in the context of
psychiatric diagnosis. Increasingly, however, the
second edition of this test (MMPI-2) has been
employed with populations that differ from those
utilised in its scale construction. However,
the degree to which this test is appropriate for
use outside of its original context, is still
largely unknown. This concern has led to the
development of new measures designed to be
sensitive to a wider variety of conditions such
as Post-Traumatic Stress Disorder (PTSD) and
Traumatic Brain Injury (TBI). This is
particularly salient to the medicolegal setting
where the MMPI-2 is the most popular measure of
psychosocial functioning in assessing personal
injury claimants (Ben-Porath, Graham, Hall,
Hirschman, Zaragoza, 1995). The current
study examines the MMPI-2 protocols of personal
injury claimants with primarily psychiatric or
neurological complaints to evaluate the degree to
which they can be discriminated using Basic
scales, Content scales, and special scales
developed specifically for this purpose.

• Discriminant Analysis was conducted using Basic
  Scales, Content Scales and each of the special
  scales with two groups PTSD and TBI (see Table
  2). These groups were chosen because of their
• Relative frequency in the sample
• The existence of specific MMPI-2 scales developed
  for their assessment
• The clarity of their respective psychiatric and
  neurological etiologies. To this end individuals
  who have sustained a TBI and are also claiming
  PTSD have been excluded from these groups.

• A sample of 3857 MMPI-2 protocols of personal
  injury claimants from forensic psychological
  practices in Australia and the United States of
  America was compiled for the purposes of this
  study. Protocols with more than 10 omitted items
  or with VRIN or TRIN T-Scores of 80 or more were
  excluded, leaving a total of 2838 cases (1391
  males, 1447 females) The mean age of the sample
  was 35.9 years (SD 13.8) with an average of
  11.8 years of education (SD 4.2).
• The diagnostic composition of the sample is
  summarised in Table 1.
• Table 1. Frequency of Diagnostic Groups

• Accuracy of discrimination between psychiatric
  (PTSD, Depression) and neurological (TBI) cases
  is insufficient to justify a discriminative role
  for the MMPI-2.
• The special scales do not increase
  classification accuracy beyond that of the Basic
  or Content scales.
• The special scales demonstrate sensitivity but
  lack the clinical specificity necessary for
  diagnostic purposes.
• Accordingly, the MMPI-2 should not be employed
  for diagnostic purposes and should be restricted
  to the descriptive role for which its item
  content, and response characteristics are
  well-suited.

Table 2. Discriminant Analyses of PTSD and TBI
Groups
The misclassification rates vary from 1 in 2 to
1 in 4 cases, with a mean of 39. Thus, on
average 1 in 3 cases would be incorrectly
classified. The special scales perform no better
than combinations of Basic or Content scales
suggesting little has been gained in terms of
classification accuracy by their
development. Table 3. Discriminant Analyses of
Depression and TBI Groups
Ben-Porath, Y. S., Graham, J. R., Hall, G. C. N.,
Hirschman, R. D., Zaragoza, M. S. (1995).
Forensic applications of the MMPI-2. Thousand
Oaks, CA Sage Jacobucci, G.D. (1993). Cerebral
impairment A new content scale for the MMPI-2.
Master of Arts Thesis, Simon Fraser
University. Keane, T.M., Malloy, P.F.,
Fairbank, J.A. (1984). Empirical development of
an MMPI scale for the assessment of
combat-related posttraumatic stress disorder.
Journal of Consulting and Clinical Psychology,
52(5), 888-891. Senior, G., Lothrop, P.,
Deacon, S. (1999). TBI(f) An MMPI-2 scale for
assessing traumatic brain injury in a forensic
setting. Poster presented at the 19th Annual
Conference of the National Academy of
Neuropsychology. San Antonio, Texas, USA. 10-13
November.
The Others group included ADHD, Bereavement,
Bipolar Disorder, CFS, Cognitive Disorder,
Dementia, Dissociative Disorder, Dysthymia,
Factitious Disorder, OCD, Phobia, Schizophrenia,
Sleep Disorder, and Whiplash.