Discriminant Function Analysis of Malingerers and Neurological Headache Patients Self- Reports of Neuropsychological Symptoms

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1 Archives of Clinical Neuropsychology, Vol. 13, No. 6, pp , 1998 Copyright 1998 National Academy of Neuropsychology Printed in the USA. All rights reserved /98 $ PII S (97) Discriminant Function Analysis of Malingerers and Neurological Headache Patients Self- Reports of Neuropsychological Symptoms Ty A. Ridenour Washington University School of Medicine Kenneth D. McCoy and Raymond S. Dean Ball State University Interpretation of a patient s neuropsychological examination involves the determination of the role motivational and psychiatric factors may have played. The ability to detect malingering becomes crucial, particularly when the examination occurs as a result of litigation. Moreover, falsely identifying a performance as distorted has serious consequences for the patient. The present study was conducted to replicate previous research that discriminated between malingered and nonmalingered responses to a neuropsychological self-report inventory. An overall hit rate of 84% for malingerers and neurologic headache patients demonstrated replication of the inventory s ability to identify malingerers. Of those predicted to be malingerers, 27% were false positives indicating the need to use this inventory in conjuction with other neuropsychological measures National Academy of Neuropsychology. Published by Elsevier Science Ltd Each year approximately two million head injuries occur in the United States (Ruff, Wylie, & Tennant, 1993). An award of financial damages when neuropsychological dysfunction can be shown is not uncommon. The possibility of financial compensation increases the probability of response distortion (Franzen, Iverson, & McCracken, 1990, Gilandas & Touyz, 1982, Lezak, 1983). Keiser (1968) argued that the potential of financial gain rarely does not play some role in the presentation of a patient with a head injury. Malingering is described as feigning or otherwise distorting symptoms of a condition to obtain some external benefit (American Psychiatric Association, 1994). Malingering differs from Factitious Disorder in that the patient s distortion of symptoms is not to maintain the sick role. Exaggerated symptoms as seen in Somatoform Disorders differs from malingering in that the former is unintentional and unlikely to receive an obvious reward. Indeed, malingering is based on external motivations including avoiding work, financial gain, and drug use (American Psychiatric Association, 1994). The authors wish to thank Cecil R. Reynolds for comments on an earlier draft. Address correspondence to: Raymond S. Dean, Neuropsychology Laboratory, TC 512, Ball State University, Muncie, IN

2 562 Ridenour, McCoy, and Dean Presently, known correlates of malingering are perhaps the best indicators available to the clinician of possible response distortion. The Diagnostic and Statistical Manual, fourth edition (DSM-IV; American Psychiatric Association, 1994) presents a number of conditions in which malingering is more likely. These conditions include a patient who is referred by an attorney, a large discrepancy between objective assessment findings and symptoms presented by the patient, lack of cooperation with evaluation and treatment, and a diagnosis of antisocial personality disorder. These indicators are less than objective. Indeed, evidence indicates these signs may need to be supplemented with other features that increase one s suspicion of malingering. Kropp and Rogers (1991) point out a greater frequency of malingering in individuals with antisocial personality disorder lacks empirical support. Detection of response distortion during the neuropsychological examination becomes paramount in the interpretation of test results (Beetar & Williams, 1995). The need for a multifaceted approach in the detection of malingering in head injured patients is underscored by the fact that the neuropsychological examination assumes patient s compliance and maximum performance (Beetar & Williams, 1995; Binder, 1990; Resnick, 1988; Rosse & Ciolino, 1986). Identification of malingering is not only for important in gaging functional loss, but in offering treatment recommendations (Nies & Sweet, 1994), limiting medical care expenses (Franzen et. al., 1990, Heaton, Smith, Lehman, & Vogt, 1978), and assessing level of disability. Estimates of the frequency of malingering vary tremendously. Some time ago, Miller (1961) reported 48 of a sample of 50 head-injured subjects showed complete recovery within 2 years of legal settlements. With the recovery of such a large proportion of the sample, the nature of Miller s sample is questioned by the results studies conducted by Mendelson (1981, 1982, 1984). Mendelson (1985) found only 25% of those patients filing for compensation had returned to work 2 years following the settlements of claims. Research efforts to identify malingering have focused on patterns of such tests as Rey s 15-item, Dot Counting, the Halstead-Retain tests, Wechsler Intelligence Scales, an assortment of tests of memory and the Minnesota Multiphasic Personality Inventories (e.g., Beetar & Williams, 1995; Iverson, Franzen, & Hammond, 1995; Mittenberg, Theroux-Fichera, Zielinski, & Heilbronner, 1995; Nies & Sweet, 1994; Zielinski, 1994). In a recent review of the literature, Nies and Sweet (1994) argued for the use of a number of measures rather than a single test in assessing the potential for malingering. Indeed, they concluded that no single test showed satisfactory hit rates for malingering. Nies and Sweet (1994) also concluded that actuarial prediction of malingering is better than clinical judgment. These authors further suggest research be conducted using self-ratings to improve the face validity of tests measuring specific symptoms (to enable malingerers exaggerations), and multivariate statistics to determine the effectiveness of malingering detection. Indicators of malingering on self-report measures include endorsement of an unusually large number of varied symptoms, failure to seek treatment, and claim of a large number of disorders prior to injury (Ruff et al., 1993). Fee and Rutherford (1988) compared the symptoms of patients seeking compensation to those not seeking compensation who had incurred similar injuries. Those seeking financial gain reported almost three times the number of symptoms of those not pursuing compensation. In spite of such evidence, psychologists have relatively few related objective measures of neuropsychological symptoms. One method for detection of symptom inconsistencies is to compare the patient s selfreport to the report of a knowledgeable informant (Nies & Sweet, 1994). Ruff and colleagues (1993) advise the clinician to contrast the patient s endorsed symptoms with those expected, given the type of injury. For symptoms that are unlikely to change with time, the consistency in patterns may be useful in ruling out suspicions of malingering (Cullum, Heaton, & Grant, 1991, Zielinski, 1994). Moreover, specific symptoms are often expected to be more pro-

3 NSI and Clinical Malingering 563 nounced immediately following injury and do not remain static during the course of recovery (Ruff et al., 1993). Therefore, patients self-report of symptoms over time may help detect inconsistencies between what is expected to occur given a particular injury and the symptoms the patient claims. The present study considered the usefulness of an inventory of a wide variety of symptoms to discriminate between malingerers and nonmalingerers. Using a self-report symptom inventory has several advantages for assessing patient malingering. This format can be used to compare responses to the layman s knowledge of head injury symptomology (Mittenburg, DiGuilio, Perrin, & Bass, 1992). A self-report inventory also allows for comparison of patients endorsed symptoms to an informant s descriptions of the patient s symptoms (Nies & Sweet, 1994) as well as tracking symptoms over the course of an injury (Ruff et al., 1993). A self-report inventory provides the clinician objective data to support a diagnosis of malingering (e.g., litigation), rather than having to rely on clinical intuition. Clearly, a false diagnosis of malingering can lead to grave injustice and should be avoided unless obvious and strong evidence exists (Ruff et al., 1993, p. 64) and an objective measure enabling obvious discrepancies between a malingerer s presentation and other sources of evidence regarding the patient s conditions is required. Intuitively, a symptom inventory may provide a method of collecting information and the need for research with such a measure is clear (Nies & Sweet, 1994). In one recent study, Ridenour, McCoy, and Dean (1996) examined symptoms for malingerers and nonmalingerers using the Neuropsychological Symptom Inventory (Rattan, Dean, & Rattan, 1989). A stepwise descriptive discriminant function analysis of symptoms resulted in a 90% overall hit rate with a mere 3.1% false positives. Because this study was conducted with traditional college students, replication with a clinical sample was recommended (Ridenour et al., 1996). Other than that conducted by Ridenour et al. (1996), little research using a self-report of inventory of symptoms in the diagnosis of malingering exists (Nies & Sweet, 1994). The purpose of the present study was to consider the utility of the Neuropsychological Symptom Inventory (NSI; Rattan, et al., 1989) in discriminating between malingerers and patients whose primary complaint was headache. Ridenour and colleagues (1996) reported no common denominators between the NSI symptom items that contributed significantly to the descriptive discriminant function. Moreover, the malingering group reported more severe impairment than the nonmalingering group on each NSI item. For these reasons, the present study focused on a summative score that consisted of all NSI item scores. A cut-off score was hypothesized and used to predict group membership in the samples of the present study. Predictive discriminant function analysis provided feedback regarding the clinical utility of the cut-off. METHOD Subjects and Procedures Subjects consisted of 77 patients without a history of head injury whose chief complaint was headache and 241 undergraduate students (malingerers) who denied a history of head injury or other neurological disorder. The headache group consisted of patients referred to a headache clinic who responded to the NSI as part of their initial work-up. Given the lack of an available sample of head-injury patients in litigation, headache patients were chosen because of the lack of medical explanation for their symptomology and the increased probability of psychological cause for medical complaints (American Psychiatric Association, 1994, pp ). All the headache patients were female and 91% were White. Sixty-nine percent of the malingerers were traditional, Caucasian female undergraduate

4 564 Ridenour, McCoy, and Dean students. Ten percent of the subjects were minority females, one was an African American male and the remaining subjects were Caucasian males. Malingerers were instructed to complete the NSI as if they were in an automobile accident and were seeking insurance compensation for a head injury. Informed consent for the malingering group was addressed by stating to subjects that no negative consequence would occur if they chose to not participate and could discontinue their participation at any time. Instrument The Neuropsychological Symptom Inventory (NSI; Rattan et al., 1989) assesses patients neuropsychological functioning in a self-report format. For the present study, subjects rated each symptom on a 4-point Likert scale. Subjects could respond to each item by circling either not at all (4), very little of the time (3), from time to time (2), or most of the time (1). A.967 Cronbach s alpha was reported for the NSI (McCoy, 1993). A fourfactor solution has been found for the NSI in two independent studies (McCoy, 1993; Jones, 1993). The four domains measured by these factors are (a) general neuropsychological functioning, (b) perceptual/motor functioning, (c) sensory/perceptual functioning, and (d) attentional/concentration functioning. For the present study, however, only total scores were considered. RESULTS The scale used for this analysis consisted of a sum of all NSI item scores. Possible total scores ranged from 400 (no symptoms endorsed) to 100 (all symptoms endorsed as occuring all the time ). The cut-off score to predict group membership as either malingerer or headache patient for this analysis was an average symptom endorsement of very little of the time or less severe. Subjects who scored 300 or lower were predicted to belong to the malingering group. Subjects were predicted to be headache patients if they scored higher than 300. A dummy coded variable indicated predicted group membership and evaluated with the discriminant function analysis (DFA) procedure (SPSS, 1993). Prior probabilities for this DFA consisted of the sample size of each group. Moreover, because of the unequal sample sizes of the two groups, improvement over the maximumchance criterion (a conservative test; Huberty, 1984) was used to evaluate the hit rate of this formula. Because a large proportion of the subjects belonged to one group, a hit rate of 76% would be found if the entire sample was diagnosed as malingerers. The success of the NSI to correctly diagnose the two groups was based on improvement over this maximum-chance criterion. Results indicated an overall hit rate of 84.3%, with 88.0% of the malingerers and 72.7% of headache patients correctly classified. Therefore, using a cut-off score of 300 reduced errors in diagnosis by 35.4% over the maximum-chance criterion. It should be noted, however, that 27.3% false positive occurred. Although this is too large a proportion to merit use of the NSI alone for clinical judgement, the NSI performed as well as or better than most neuropsychological tests and batteries (Iverson, Franzen, & McCracken, 1994; Nies & Sweet, 1994; Pope, Butcher, & Seelen, 1993; Tenhula & Sweet, 1996; Zielinski, 1994). The amount of shrinkage that could be expected if this study were conducted with an entire population was estimated using Wherry s (1932) formula (see also Lord & Novick, 1968, p. 286; Reynolds, 1997, p. 195). The canonical correlation found for the present discriminant function was.5875 (R ). Wherry s formula estimated that a squared correlation of.3431 would be found for the population, indicating that virtually no shrinkage

5 NSI and Clinical Malingering 565 would occur (r.5875). Therefore, it is very probable that these results would be replicated in a similar sample. DISCUSSION The results of the present study indicate the NSI may be useful in identifying malingerers. To date, research regarding malingering detection with self-report inventories has not produced satisfactory results (Pope et al., 1993; Nies & Sweet, 1994). The fact that the NSI cutoff score produced replication of improved identification of malingerers over the maximumchance criterion indicates that the NSI is likely to fill the void of a self-report inventory with utility for detection of response distortion. Moreover, because the NSI is a record of self-reported symptoms, detection of malingering can be aided in ways that are nonstatistical (see Ruff et al., 1993). For example, evidence of response distortion can be produced when inconsistencies occur between endorsed items and symptomology that is expected given a particular patient s injury. The NSI could be administered on two different occasions because the chance of similar item endorsement is lower for malingerers. The NSI can also be administered to the patient and an informant who is close to the patient to evidence inconsistencies between the two reports. Furthermore, the clinician has record of the patient s responses should a question of response distortion occur. Further research should address questions regarding the use of self-report inventories to detect malingering. For example, little data are available that address gender differences in the self-report presentation of malingering. Moreover, cultural and/or racial differences may be found in which the discriminant function used in this study may not differentiate certain groups from malingerers as well as the largely Caucasian, female sample of this study. One shortcoming of the present study is the fact that undergraduate students were used as the malingering sample. Although college undergraduates are just as capable of malingering as other populations, patients who malinger are likely to be more heterogeneous. Given the present results, research examining the malingering patterns of noncollege populations could be conducted by administering the NSI to patients who are seeking financial compensation. These patients could be divided into two groups to facilitate DFA, one of which consists of those who have a higher predisposition to malinger. For example, the DSM-IV indicates that patients diagnosed with antisocial personality disorder and patients with an addiction are more likely to malinger. Another way to determine patients who are likely to be malingerers has been demonstrated in follow-up studies that have focused on patients returned to work soon after receiving benefits (see Miller, 1961; Mendelson, 1981, 1982, 1984). Nies and Sweet (1994) show that detection of malingering should rely on more than one measure. The incorporation of the NSI with other neuropsychological measures that have been shown to discriminate between a group of malingerers and nonmalingerers should be considered. Combining the NSI with other neuropsychological measures, such as tests of cognitive ability (Haines & Norris, 1995) are likely to result in better hit rate than those reported in the present study or hit rates found with another neuropsychological measure alone. Patients who complain of severe headaches often do not have a physical cause for the headache. Such patients may actually present with a somatoform disorder. Therefore, it is likely that a portion of the headache complaints of the sample of this study may have been in part due to psychological dysfunction rather than a physical cause. Although speculation regarding the accuracy of the NSI to discriminate between malingerers and patients with a somatoform disorder requires research that specifically contrasts these two populations, these

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