Homogenous Base Rates for Malingering in Neuropsychological Examination of Litigants

Abstract

Base rates for malingering are often obtained and averaged across multiple clinicians who apply heterogeneous methods for detection (Mittenberg et al., J Clin Exp Neuropsychol 24: 1094−1102, 2002; Young, Psychol Inj Law 8: 200–218, 2015). Our aims of obtaining homogenous base rates included the following: (a) evaluation of all our legal cases in accordance with the guidelines set forth in the position papers by both the National Academy of Neuropsychology and the Association for Psychological Advancement in Psychological Injury and Law, (b) minimal variation between our comprehensive neuropsychological examinations, and (c) determination of base rates of failed effort in 150 consecutively examined legal cases in one medical setting. To assess the various levels of volitional exaggeration, we introduced four gradations of poor effort definitions, which relied on performance validity tests (PVTs). A comparison between two consecutive samples of 75 litigants indicated less frequent poor effort with increasingly more conservative criteria. In our analysis of a subset of litigants who sustained traumatic brain injuries (N = 115), the four base rates for mild versus moderate-severe TBI groups were equivalent for the two more lenient malingering definitions but varied for the two more conservative definitions. Specifically, for the mild TBI cases investigated, the percentage of three PVT failures (or one PVT failure significantly below chance) arrived at 3.4 %. Our final aim was to compare the base rates of poor effort that were obtained with PVTs to the base rates of emotional and physical symptom endorsement, which were obtained with symptom validity tests (SVTs). No significant correlations emerged in this analysis. The discussion emphasizes the relatively lower base rates of poor effort found in the convenience sample studied in neuropsychological evaluations relative to the higher estimates in the literature (40 +/− 10 %, Larrabee et al., Clin Neuropsychol 23: 841–849, 2009) but not others based on comprehensive review (Young, Psychol Inj Law 8: 200–218, 2015).

Appendices

Appendix 1

Method Used for Determining Poor Effort—Procedures

• (a) Remain abreast of trends in the symptom validity assessment literature. Approach the assessment of symptom validity proactively.

• (b) Assess whether cognitive, psychiatric, and/or behavioral symptoms are embellished.

• (c) Use a multi-method approach. A distinction is made between a multi-method approach and a multi-test approach. Whereas the administration of multiple tests may or may not contribute incrementally to the validity of the clinical determination, the use of multiple methods that extend beyond testing is likely to contribute to such validity

• (d) Inform the examinee at the outset of the evaluation and as needed during the evaluation that good effort and honesty will be required (the examiner may inform the examinee that such factors will be directly assessed).

• (e) Use SVTs with the most appropriate psychometric properties, given the characteristics of the examinee and setting.

• (f) Disperse SVTs or measures with symptom validity indicators throughout the evaluation, with administration of at least one SVT early in the evaluation process.

• (g) Report the results of symptom validity assessment

Source: Bush et al. (2005).

Appendix 2

Further Methods Used for Determining Poor Effort

• (a) Data from SVTs should generally be given substantially greater weight than subjective indicators of suboptimal effort. Subjective indicators, such as examinee statements and examiner observations, should be afforded less weight due to the lack of scientific evidence supporting their validity. Invalid performance on a measure of personality does not allow for an a priori conclusion that the neurocognitive test results are also unreliable, and vice versa.

• (b) The examiner must consider the nature of the performance on SVTs and other evaluation findings when generalizing from the results of SVTs to other test results.

• (c) Strong evidence of invalid performance on SVTs or other indicators of symptom validity raise doubt about the validity of all neurocognitive test results. In the presence of invalid performance on measures or indices of symptom validity, interpretation of performances on other tests as valid would need to be justified.

• (d) When evidence of invalid performance exists, scores on cognitive ability tests may be interpreted as representing the examinee’s minimum level of ability.

• (e) Performance slightly below cutoff on one SVT may not justify an interpretation of biased responding; converging evidence from additional indicators may be required.

• (f) If an evaluation that has been discontinued due to insufficient effort or invalid responding is later continued, the confidence that could be placed in the validity of the results would remain limited.

Appropriate probabilistic language based on the nature and extent of convergent evidence should be employed when offering explanations for symptom exaggeration or fabrication (see, for example, Slick et al., 1999). Vague or misleading terminology to describe invalid performance should be avoided.

Source: Bush et al. (2005).