RECOMMENDATIONS

1
Detecting Psychosocial Exaggeration Base Rates
of the MMPI-2 Validity Index in Community
Controls and Personal Injury Claimants Graeme
J. Senior, Ph.D., University of Southern
Queensland, Australia, Rael T. Lange, Ph.D.,
Riverview Hospital, Canada, Lucille A.
Douglas, Ph.D., Assessment Services in
Psychology, Australia
INTRODUCTION The MMPI-2 Validity Index is a
recently developed composite which utilises seven
different validity measures (see table 1) from
the MMPI-2 (Meyers, Millis, Volkert, 2002).
These authors utilised three groups chronic
pain patients not in litigation, chronic pain
patients in litigation, and knowledgeable actors
who were asked to malinger on the MMPI-2. A cut
score of 5 or more on the Validity Index was
recommended by these authors as it did not
misclassify any of the non-litigants and
correctly identified 86 of the malingerers.
However, only 64 of the chronic pain cases in
litigation scored below the cut-off suggesting
that 1 in 3 of these litigants would be suspected
of exaggeration.   The objective of the current
study was to examine the accuracy of the
recommended cut-score in a large sample of
personal injury claimants. PARTICIPANTS Normati
ve Sample 310 Community volunteers Mean Age
24.4 (SD 6.6) Mean Education 12.7 (SD
1.5) Gender Male (n 124) Female (n 186)
Participants were excluded if they reported any
history of psychiatric or neurological
disorders. Clinical Sample 1150 Personal
injury claimants from a private practice
Brisbane, Queensland. Diagnostic groups
phobias, chronic pain (Pain),
somatoform/conversion disorders, traumatic brain
injury (TBI), Anxiety disorders, Adjustment
disorders, panic disorder, Depression, Post-
traumatic stress disorder (PTSD), substance
abuse (ETOH/Drug), suspected malingerers.
Mean Age 37.7 (SD 12.0) Mean Education
11.4 (SD 3.0) Gender Male (n 633) Female
(n 517) MEASURES The Second edition of the
Minnesota Multiphasic Personality Inventory
(MMPI-2) was administered to all clinical
cases as part of a psychological assessment
related to their personal injury claim. The
Community Normal sample was assessed as a
part of ongoing normative studies. Validity
Index scores were computed for all cases
using the measures weightings indicated in
Meyers et al. (2002) which are presented in
Table 1.
RESULTS Table 2. Cumulative percentages of the
MMPI-2 Validity Index by Diagnostic Group
Table 3. Test Operating Characteristics of the
Recommended Cut-score of 5 for the Validity
Index in Discriminating Malingerers from
Other Diagnostic Groups in the Personal Injury
Claimant Sample (Sensitivity .76)
PPP positive predictive power NPP negative
predictive power OPP overall predictive power
RECOMMENDATIONS The purpose of such tables
is to guide clinicians in their
decision-making with regard to the likelihood of
simulation of symptom exaggeration on the
MMPI-2. As is often the case, no one
cut-off will optimally discriminate all
groups. Clinicians can be confident that
Validity Index scores of 11 are extremely
rare in personal injury claimants
(occurring in no more than 5 of any clinical
group) and strongly suggest exaggeration.
The expected base rate of such a score in
malingerers in this sample is 36. The
consequence of applying a lower cut-off is that
the clinician may over-identify exaggeration
depending upon the nature of the claimed
disorder. Scores in the range of 6 while
suggestive of exaggeration (encompassing 68
of the suspected malingerers scores) should
be considered in the context of the nature
of the personal injury claim. Conditions
such as depressive illness, PTSD, and
substance abuse, for example, produce 23 to 32
of their scores in this range. REFERENCES
Meyers, J.E., Millis, S.R., Volkert, K.
(2002). A validity index for the MMPI-2. Archives
of Clinical Neuropsychology, 17, 157-169.
RESULTS Table 2 provides the cumulative
percentages of cases with specific Validity
Index scores. No clinical cases scored
greater than 12 on the Validity Index The
results suggest that if a cut of 5 is used then 1
in 6 medicolegal cases (17.3) would be
interpreted as reflecting exaggeration.
32.2 of the Pain sample produced Index scores
at or above the cut-off. This compares
favourably to the 36 of chronic pain
litigants who produced Index scores at this
level in the Meyers et al. (2002) study. 76
of the suspected malingers in the current study
produced Index scores at or above the cutoff
as compared to the 86.7 reported for the
knowledgeable actors asked to malinger in
Meyers at al. (2002). Table 3 illustrates
the predictive powers of the Validity Index
in the medicolegal sample with respect to
differentiating between the Malingering and
other clinical groups. Positive predictive
power indicates the probability that a particular
case is from the Malingering group knowing
only that they obtained a Validity Index
score above the cutoff. When the prevalence
of the two groups is close to .5 positive
predictive power is generally high. However, as
the prevalence approximates the 15-30 more
commonly associated with the medicolegal
setting, PPP drops substantially.
Negative predictive power remains generally high
indicating that Validity Index scores below
the cutoff are characteristic of clinical
group performance.
Table 1. Measures Weightings Comprising the
MMPI-2 Validity Index