Head injury and the ability to feign neuropsychological deficits

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1 Archives of Clinical Neuropsychology 19 (2004) Head injury and the ability to feign neuropsychological deficits Chad D. Vickery, David T.R. Berry, Chantel S. Dearth, Victoria L. Vagnini, Raymond E. Baser, Dona E. Cragar, Stephen A. Orey Abstract Department of Psychology, University of Kentucky, 115 Kastle Hall, Lexington, KY , USA Accepted 25 July 2002 This study investigated the possibility that head-injured patients, by virtue of their exposure to medical and legal evaluations, are better able to feign deficits than controls. Both internal and external validity issues were addressed in a malingering simulation using 46 moderately to severely head injured and 46 matched control subjects who were administered a battery of neuropsychological and motivational tests under standard or malingering instructions. Results showed no significant interaction between malingering instructions and head injury status on commonly used motivational tests or neuropsychological tests, nor were the head injured malingerers better able to avoid detection using established cutting scores on motivational tests. These results suggest that head injured individuals are no more able to feign neuropsychological deficits successfully than non-head injured individuals National Academy of Neuropsychology. Published by Elsevier Ltd. All rights reserved. Keywords: Head-injured patients; Neuropsychological deficits; Malingering 1. Introduction Since the 1980s, clinical and research interest in detecting feigned neuropsychological deficits has intensified (Larrabee, 2000; Reynolds, 1998; Sweet, 1999). One important factor here has been the demonstration that relatively unsophisticated individuals may successfully This paper is based on a dissertation submitted by Chad Vickery in partial fulfillment of the requirements for a doctorate in clinical psychology. Corresponding author. Tel.: ; fax: address: dtrb@uky.edu (D.T.R. Berry) /$ see front matter 2002 National Academy of Neuropsychology. PII: S (02)

2 38 C.D. Vickery et al. / Archives of Clinical Neuropsychology 19 (2004) portray deficits on neuropsychological testing (Faust, Hart, & Guilmette, 1988). A second major factor has been the increasing acceptance of neuropsychological results in legal and administrative settings determining substantial benefits (Taylor, 1999). Patient honesty may not be taken for granted in compensation-seeking circumstances (Berry, Baer, Rinaldo, & Wetter, 2002). As neuropsychologists have developed and validated objective tests for the detection of malingered cognitive deficits in response to concern about feigning of deficits, increasing attention has been devoted to the quality of the underlying research in the area. Rogers (1997) systematically reviews methodological issues in research on the detection of feigned psychological deficits and identifies a number of important concerns involving issues of internal and external validity. Internal validity, or confidence that the experimental manipulation is the sole explanation for changes in the dependent variable, is usually higher in simulation (analog) designs, which typically involve instructing normal individuals to feign deficits with results compared to those from genuine patients. In contrast, external validity, or generalizability of findings, tends to be higher in known-groups designs which involve independently identified groups of honest and feigning patients from clinically relevant settings. Rogers (1997) recommends converging support from both types of designs before accepting a malingering detection procedure as valid. An alternative strategy involves minimizing the weaknesses of each type of design. For example, Rogers suggests a four group design crossing the factors of patient status (patient or normal) and instruction set (feigning or honest). Rogers proposes other refinements such as post-test checks on compliance of participants with their instructions, use of specific scenarios for believable feigning that participants may easily identify with, provision of coaching information likely to be obtained by real-world feigners, and offering incentives for successful feigning to make the experimental situation more comparable to real-world circumstances. The present investigation attempted to fulfill Rogers (1997) suggestions for increasing experimental rigor in an analog study of the detection of malingered neuropsychological deficits. Head-injured (HI) patients and matched controls were instructed to feign or answer honestly while completing a battery including malingering and standard neuropsychological tests. Perhaps the most clinically relevant feature of the study was a test of the possibility that HI individuals, by virtue of their direct experience with head injury and related medical and legal procedures, might be better at feigning deficits than normals (Haines & Norris, 1995; Hayes, Hilsabeck, & Gouvier, 1999; Nies & Sweet, 1994). 2. Method 2.1. Participants Prospective HI participants were recruited by fliers in waiting rooms of appropriate clinical specialists, announcements at head injury support group meetings, and advertisements in newspapers. HI participants were required to have experienced a head injury that resulted in loss of consciousness for 1 h, undergone evaluation in a regional medical center, be willing to sign releases for medical records, have no current involvement in any form of compensation-seeking,

3 C.D. Vickery et al. / Archives of Clinical Neuropsychology 19 (2004) and have no significant substance abuse history. Most of the initial 49 HI subjects had been injured in moving vehicle accidents with the remainder experiencing falls (18%) or assaults (11%). All HI participants denied current compensation-seeking, although 60% indicated that they had done so in the past. The 53 initial community volunteers (CVs) were recruited through advertisements and fliers in business and entertainment establishments. CV participants were matched to HI groups on demographic characteristics and required to have no history of significant neurological, psychiatric, or substance abuse or history of head injury with positive loss of consciousness Materials All participants completed an IRB approved informed consent agreement, demographic & medical questionnaires, a battery including both motivational and standard neuropsychological tests and a post-testing debriefing form requesting ratings using a 10-point scale (from low (0) to high (10)) on understanding, memory, compliance, and effort to follow instructions. HI participants also received the Mini Mental Status Examination (MMSE: Folstein, Folstein, & McHugh, 1975), to evaluate capacity to provide informed consent, and completed a release form providing permission to obtain medical records regarding their head injury. A Coaching Sheet was prepared for malingering participants. This material included commonly experienced head-injury symptoms as described on websites of eight state or national brain injury foundations and eight attorneys who provided such information. Symptoms appearing in at least half of each web site type were included. Additionally, tips for avoiding detection as a malingerer from previous studies (Frederick & Foster, 1991; Inman et al., 1998; Martin, Bolter, Todd, Gouvier, & Nicholls, 1993; Rose, Hall, & Szaldi-Petree, 1998) were included. Because of ethical concerns regarding publishing information that might compromise the validity of psychological tests (Ben-Porath, 1994; Berry, Lamb, Wetter, Baer, & Widiger, 1994), this information is available on request from the corresponding author. Standard neuropsychological tests administered to all participants included the Controlled Oral Word Association Test, Digit Span and Digit Symbol subtests of the WAIS-III, the Finger Oscillation Test, Word List Immediate and Delayed subtests from the WMS-III, the Grooved Pegboard Test, the New Adult Reading Test Revised, and the Stroop Color-Word Reading Test. Extensive information on these well-established neuropsychological tests is available in Lezak (1995) and Wechsler (1997). Raw scores from Wechsler series tests were transformed to scaled scores, whereas remaining tests were transformed to T-scores using the Heaton, Grant, and Matthews (1991) norms. Malingering tests included the Digit Memory Test (DMT; Hiscock & Hiscock, 1989) modified to Guilmette, Hart, Giuliano, and Leininger s 36-item short form (1994), Test of Memory Malingering (TOMM; Tombaugh, 1997), and Letter Memory Test (LMT; Inman et al., 1998). The DMT is a forced-choice digit recognition test with increasing delays that has been extensively validated and found to have a large effect size (Cohen s d) in a recent meta-analysis of malingering procedures (Vickery, Berry, Inman, Harris, & Orey, 2001). Internal consistency reliability for the DMT has been adequate at.87 (Inman et al., 1998). A cutting score of <90% correct has been validated to identify inadequate motivation on the DMT (Vickery et al., 2001).

4 40 C.D. Vickery et al. / Archives of Clinical Neuropsychology 19 (2004) The TOMM (Tombaugh, 1997) involves forced-choice recognition of simple line drawings in immediate and delayed trials and is insensitive to depression (Rees, Tombaugh, & Boulay, 2001). A cutting score of <90% correct on the second of two learning trials or on a delayed recognition trial has been demonstrated to have high sensitivity and specificity by Rees, Tombaugh, Gansler, and Moczynski (1998). The LMT (Inman et al., 1998) is a forced-choice test of motivation that uses consonant letters as stimuli in 45 trials crossing the factors of number of stimuli to be remembered (3, 4, or 5) and number of foils (1, 2, or 3) presented with the target stimulus. Inman et al. reported large effect sizes for the LMT when comparing HI controls to analog feigners (2.0) or to forensic patients independently identified as probable feigners (3.5). Internal consistency reliability was approximately.94. The LMT was insensitive to depression, and using a cutting score of <93% correct, Inman et al. found sensitivities ranging from 83 to 95% and a specificity rate of 100%. Orey, Cragar, and Berry (2000) and Inman and Berry (2002) found comparable specificities but lower sensitivities Procedure HI and CV participants who met screening requirements were evaluated by two research assistants. RA1 explained the study, obtained consent, supervised completion of the history forms, and administered the NART-R under standard instructions. For HI participants, RA1 also obtained the medical release and administered the MMSE under standard instructions. Using a criterion of <24 on the MMSE, no participants were excluded for potential inability to provide informed consent. All participants were randomly assigned by RA1 to control or malingering instructions, creating four groups: HI Controls (HIC), HI Malingerers (HIM), CV Controls (CVC), and CV Malingerers (CVM). HIC and CVC participants were instructed by RA1 to perform to the best of their ability on subsequent tests, but not to reveal their instructions to RA2 who would test them. They were also told that they would receive $75.00 at the end of the study. HIM and CVM participants were told by RA1 that they would receive a minimum of $75.00 for participation and a bonus of $20.00 if they successfully fulfilled instructions without being detected. They then read a detailed scenario describing an evaluation to determine readiness to return to work following a head injury. They were asked to imagine that they were not able to return to work and were to complete the tests to document disability. They were cautioned to avoid obvious feigning and detection. They were then given the Coaching Sheet and time to consider how they would approach the testing. When they indicated their readiness to begin, RA1 checked for any questions, cautioned them not to reveal their instructions to RA2 and reminded them of the potential bonus for successful feigning. RA2, blind to the instruction set, administered the tests in a counterbalanced order, following standard procedures with brief rest breaks as needed. After completion of testing, RA1 replaced RA2 and requested completion of post-test debriefing forms. HIC and CVC participants were then paid the honorarium of $75.00 and allowed to leave. HIM and CVM participants were asked to complete the post-test forms while their tests were scored. RA1 left the room during this time and returned to tell each malingering participant that he or she had won the bonus and provided the $95.00 honorarium.

5 C.D. Vickery et al. / Archives of Clinical Neuropsychology 19 (2004) Obtained data were screened to increase internal validity. Two HI participants were dropped for inadequate injury severity indicators and one was dropped for a history of severe psychopathology, leaving 23 in both the HIM and HIC groups. Five CV participants were eliminated for a self-reported history of head injury with positive loss of consciousness. Only a single participant provided an outlying low rating on any of the feedback scales (<6) and this CV subject was dropped, leaving 23 in both the CVM and CVC groups. 3. Results Medical records for HI participants indicated that these patients had generally experienced moderate to severe head injuries. Mean admitting GCS rating was 8.6 (S.D. = 4.1), 85% had positive neuroimaging results (CT or MRI), and 34% had neurosurgical intervention. HI participants reported that they were a mean of 61.7 months post-injury (S.D. = 40.5), had a mean duration of loss of consciousness of 13.8 days (S.D. = 20.1), and a mean duration of post-traumatic amnesia of 41.3 days (S.D. = 47.9). Comparison of the HIM and HIC groups on these parameters using t-tests or chi-square procedures indicated no statistically significant differences (all Ps >.05). Table 1 presents demographic and other relevant variables for the experimental groups. Application of 2 2 ANOVA or log-linear chi-square procedures revealed no significant interactions of the instructional set and head injury factors on any variable or any significant main effects for instruction set; thus, only univariate main effects for the HI factor are presented in Table 1. Evaluation of the main effects indicated that the groups were comparable on all variables except NART-R estimated Full Scale IQ, where a main effect for head injury status reflected significantly lower IQ estimates for HI participants (F(1, 88) = 8.86, P =.004) and history of psychiatric treatment (χ 2 (1,N = 92) = 26.36, P<.001) where a similar effect indicated that HI participants were more likely to report psychiatric treatment. Although not shown in the table, no significant differences were found on current or premorbid occupational status using the WAIS-R occupational categories (Wechsler, 1981). Results from standard neuropsychological tests appear in Table 2 and were analyzed using Pillai s Trace, which is robust to violations of variance assumptions provided there are an equal number of subjects in each cell (Bray & Maxwell, 1985). A 2 2 MANOVA revealed significant main effects for instruction set (Pillai s Trace =.379, approximate F(9, 72) = 3.99, P<.001) and head injury (Pillai s Trace =.346, approximate F(8, 72) = 3.46, P =.001) but no significant interaction (Pillai s Trace =.150, approximate F(9, 72) = 1.16, P =.334). In light of the multiple statistical tests, evaluation of univariate main effects used a conservative P<.005 criterion for statistical significance. Univariate ANOVAs indicated reliably lower scores (P <.005) for malingering groups on seven of nine variables with a median d of 1.1. Reliably lower scores were also found for HI groups on five of nine variables, with a median effect size of.89 (Cohen s d; Cohen, 1977). Thus, on standard neuropsychological tests, effect sizes of head injury and malingering instructions were large and comparable. The non-significant interaction term suggests no differential ability of HI participants to feign successfully and this conclusion was supported by the low d scores for the interaction terms for the ANOVAs (median d =.11).

6 42 C.D. Vickery et al. / Archives of Clinical Neuropsychology 19 (2004) Table 1 Characteristics of four experimental groups Variable HIM HIC CVM CVC P (HI) Age M S.D Education M S.D NART-R M S.D No. of drinks M S.D Male (%) White (%) Right (%) Psych (%) <.001 Note. P = probability for ANOVA term; HIM = Head-Injured Malingerers; HIC = Head-Injured Controls; CVM = Community Volunteer Malingerers; CVC = Community Volunteer Controls; HI = Head Injury Status main factor. Age and education given in years. NART-R = WAIS-R estimated Full Scale IQ; No. of drinks = reported number of alcoholic drinks per week; Male = percentage of group of male gender; White = percentage of group of Caucasian ethnic background; Right = percentage of group reporting right hand dominance; Psych = percentage of group reporting history of psychiatric treatment. =significant at the.05 level. Table 3 presents results from the motivational tests. A 2 2 MANOVA indicated a significant main effect for instruction set (Pillai s Trace =.466, approximate F(4, 81) = 17.64, P<.001). However, no significant effect of head injury status (Pillai s Trace =.054, approximate F(4, 81) = 1.15, P =.34) or interaction effect was observed (Pillai s Trace =.054, approximate F(4, 81) = 1.15, P =.34). In light of the non-significant interaction, as well as low ds for the interaction terms (median d =.11) only the main effect of instructions was explored using univariate ANOVAs and presented in Table 2 with a P<.005 threshold for significance (main effects for head injury status are included for comparison). Significantly lower scores were noted for malingerers on every motivational test. The d scores indicate minimal effect sizes for head injury status, but very large effects for instruction set. This indicates that the motivational tests were quite sensitive to instruction set, but insensitive to the presence of head injury. The lack of a significant interaction effect suggests no differential ability of HI participants to avoid detection on motivational tests. Classification parameters for each test using the recommended cutting score are presented in Table 4. Chi-square tests failed to reveal significant differences between HI and CV groups on any classification parameter, providing no evidence for differential ability to feign successfully by head injury status.

7 C.D. Vickery et al. / Archives of Clinical Neuropsychology 19 (2004) Table 2 Standard neuropsychological test results from four experimental groups IS HIS Variable HIM HIC CVM CVC P d P d Digit span M S.D Word lists (imm recall) M S.D Word lists (del recall) M S.D Word lists (recog) M S.D Digit symbol M S.D Finger tapping (dom) M S.D Grooved pegboard (dom) M S.D COWA M S.D Stroop PR M S.D Note. P = probability for main effects of IS and HIS factors; IS HIS not shown; d = Cohen s d-value effect size; Digit span through Digit symbol given as scaled scores. Finger tapping through COWA given as T scores. To evaluate further the question of differential feigning ability by head injury status, a malingering success variable was created. A successful malingerer was defined as one who obtained one or more impaired scores ( 5th percentile) on standard neuropsychological tests and passed (above the cutting score) all motivational tests. All other combinations were deemed failed malingerers. Using these definitions, one (4.3%) individual in the HIM group was a successful malingerer as were 3 (13%) individuals in the CVM group. These proportions were not significantly different (χ 2 (1,N = 92) = 1.09, P =.30), failing to suggest any superiority in malingering for HI participants.

8 44 C.D. Vickery et al. / Archives of Clinical Neuropsychology 19 (2004) Table 3 Motivational test results from four experimental groups Variable HIM HIC CVM CVC P d P d LMT M S.D DMT M S.D TOMM (Trial 2) M S.D TOMM (retention) M S.D Note. P = probability for ANOVA term; HIM = Head-Injured Malingerers; HIC = Head-Injured Controls; CVM = Community Volunteer Malingerers; CVC = Community Volunteer Controls; P = P value; IS = Instructional Set main factor; HIS = Head Injury Status main factor; IS HIS not shown; d = Cohen s d-value effect size; LMT = Letter Memory Test; DMT = Digit Memory Test; TOMM = Test of Memory Malingering; All values given as percent correct. Table 4 Classification rates for motivational tests by procedure and head injury status Participants Test HI CV HI + CV P LMT Sens Spec HR DMT Sens Spec HR TOMM a Sens Spec HR Note. P = probability for χ 2 test comparing results from HI and CV participants; LMT = Letter Memory Test; DMT = Digit Memory Test; TOMM = Test of Memory Malingering; Sens. = sensitivity, percentage of HIM or CVM groups correctly classified at cutting score; Spec. = specificity, percentage of HIC or CVC groups correctly classified at cutting score; HR = overall hit rate, percentage of all groups correctly classified. a Failure on the TOMM is determined by <90% correct performance on either Trial 2 of the learning trials or on the delayed retention trial, as per normative guidelines; therefore, only one value is reported for the TOMM on this table. IS HIS

9 C.D. Vickery et al. / Archives of Clinical Neuropsychology 19 (2004) Table 5 Classification rate data requiring failure of increasing numbers of motivational tests for identifying malingering BR = 15% BR = 40% BR = 50% No. of tests failed Sens. Spec. HR PPP NPP PPP NPP PPP NPP Note. BR = base rate, percentage of individuals in sample who were malingering; No. of tests failed = number of motivational tests in which individual s performance falls below cutting score (see text); Sens. = sensitivity, percentage of malingering groups (HIM + CVM) falling below cutting score; Spec. = specificity, percentage of honest groups (HIC + CVC) falling above cutting score; HR = hit rate, percentage of both groups correctly classified by cutting score; PPP = positive predictive power, percentage of those with positive test sign who were malingering; NPP = negative predictive power, percentage of those with negative test sign who were not malingering. In clinical practice, it is common for multiple motivational tests to be administered, although empirical evaluation of decision strategies in this situation is rare (Inman & Berry, 2002; Iverson & Franzen, 1996). Table 5 explores the effect of increasingly stringent criteria for identifying motivational impairment using DMT, TOMM, and LMT results from the combined HI and CV groups. Considering only basic classification parameters, the highest hit rate is achieved using a criterion of failing one or more motivational tests. However, the usual tradeoff between sensitivity and specificity is seen with increasingly stringent criteria. Table 5 also provides clinically relevant data on positive predictive power (PPP) and negative predictive power (NPP) at three base rates of malingering. PPP is the probability that an individual with a positive test sign in fact has the condition in question. NPP is the probability that an individual with a negative test sign does not have the condition in question (Gouvier, Hayes, & Smiroldo, 1998). Inspection of PPP and NPP data at various base rates indicates that in low base rate environments (15%), NPP is usually high whereas PPP is lower. Thus, in low base rate environments, a more conservative threshold for predicting malingering may be appropriate, such as requiring that three or more malingering tests be failed (PPP = 100%; NPP = 89.4%). In contrast, in settings where the base rate of malingering is high (50%), using conservative criteria to predict malingering, such as requiring that three or more motivational tests be failed, results in high PPP (100%) but unacceptably low NPP (59.4%). More liberal criteria for predicting malingering may be appropriate in high base rate settings. These issues must be carefully weighed before adopting any decision strategy. 4. Discussion This study compared neuropsychological and motivational test results from HI and CV participants responding honestly or malingering deficits. Steps taken to increase internal validity including matching groups on demographic variables, providing detailed specific scenarios, allowing malingering participants time to formulate a feigning strategy, and screening participants for compliance with instructions. Measures to increase external validity included

10 46 C.D. Vickery et al. / Archives of Clinical Neuropsychology 19 (2004) blinding test administrators to participant instructions, administering multiple motivational tests in the context of a neuropsychological battery, providing coaching information from easily available sources, warnings to feign believably, offering financial incentives for successful malingering, and using clinically relevant samples. Results from both neuropsychological and motivational tests showed no interaction of instruction set and head injury status. Similarly, there were no significant differences between HI and CV groups on a malingering success variable. Overall, HI and CV participants were quite comparable as they followed their instructional sets with no evidence for malingering superiority in those with the experience of a significant head injury. These results are consistent with other reports that have failed to find a significant effect of head injury on ability to malinger successfully (Hayes, Martin, & Gouvier, 1995; Inman & Berry, 2002; Ju & Varney, 2000; Rees et al., 1998). Based on the present study and other literature, whatever factors may contribute to ability to feign successfully, simply experiencing a genuine head injury does not appear to be one of them. However, while the present methodology provided general strategies to facilitate malingering, presentation of very specific information on motivational tests by interested individuals would likely compromise their effectiveness (Youngjohn, 1995). Both head injury and malingering instructions resulted in depressed scores on standard neuropsychological tests. The effect sizes for these two variables were large and quite comparable, emphasizing the importance of ruling out malingering as an explanation for impaired scores on testing (Larrabee, 2000). Results from motivational tests showed a main effect for instruction set but not for head injury status and no interaction. These results suggest that the motivational tests studied here, as intended by their developers, are overwhelmingly more sensitive to feigning than to presence of a head injury. Classification rates for each motivational test indicated moderately high to perfect specificity at recommended cutting scores, low to moderately high sensitivity, and moderate to moderately high overall hit rates. Overall, results from the classification data were supportive of all of the motivational tests studied here. However, in clinical practice, it is common to administer multiple motivational tests. Consistent with the earlier findings of Iverson and Franzen (1996) and Inman & Berry (2002), the highest hit rates for test combinations in the present study were obtained using a criterion of one or more positive findings on these tests to identify malingering. However, in low base rate environments, it would be necessary to use a conservative criterion to achieve acceptable PPP. Results also emphasized that when base rates for malingering are high, NPP will be unacceptably low if the criterion for predicting malingering is too stringent. Of course, these results would change if other motivational tests with different operating characteristics were used. These issues must be carefully considered when interpreting results from motivational tests. Limitations of the present study include the modest number of participants in each group, the significant length of time that had passed between experiencing the injury and current testing in the HI participants, the modest financial incentive offered for successful malingering, use of a short form of the DMT, the arbitrary threshold used to screen for compliance on feedback variables, and the differences on estimated Full Scale IQ and psychiatric history between HI and CV groups. These last results are consistent with previous reports of lower IQs following head injury (Kane, Parsons, & Goldstein, 1985) and the treatment for psychiatric disorders that

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