Assessing Validity in Fitness to Stand Trial: The Role of Cumulative Binomial Probability

Psychiatry, Psychology and Law | 2024, p. 1-17

What are the chances? – Validity assessment and the cumulative binomial distribution in the evaluation of fitness to stand trial

Jon Nuth; Department of Psychological Medicine, University of Auckland, Auckland, New Zealand

Shoni Marshall-Edwards; Department of Clinical Psychology, Massey University, Auckland, New Zealand

James Webb; Traumatic Brain Injury Network, Auckland University of Technology, Auckland, New Zealand

This paper describes the case of a defendant accused of homicide who exhibited amnesia, mental health difficulties and widespread cognitive impairments, casting doubt on his fitness to stand trial. Court-ordered assessments opined that he was unfit to stand trial. This paper describes further assessment and the creation of a novel forced-choice performance validity test (PVT) specific to the defendant’s autobiographical memory and legal circumstances. Symptom validity tests (SVT) were administered to assess the veracity of observed mental health phenomena. The obtained results indicated statistically below chance performance and the feigning of several phenomena. To aid the Court, cumulative binomial probability values were also presented. The paper describes the findings made by the sentencing and appellate courts. It concludes by recommending, with reference to this case study, the use of recently proposed Multidimensional Malingering Criteria for Neurocognitive, Somatic, and Psychiatric Malingering.

 Culture; dissociative amnesia; feigning; fitness to stand trial; malingering; homicide; validity assessment

“In cases of serious criminal charges such as homicide, defendants are often referred for mental health evaluations because of concerns raised by legal counsel or the Court. Concerns may relate to understanding police cautions, competence to waive the right to counsel, fitness/competence to stand trial, and aspects of criminal culpability (e.g. mens rea, criminal insanity, voluntariness/ automatism). When they are suspected, mental impairments typically resemble the clinical features of: (a) mental health distress (e.g. psychosis), and/or, (b) impaired cognitive /intellectual ability (e.g. acquired brain injury). Spanning both domains, crime-related or offence-related amnesia may also be claimed” (p. 1).

"This paper describes the case of R v Malik [2015]; a New Zealand male of Pakistani origin who faced two counts of homicide. Following his arrest, and throughout subsequent inquiries, he presented with an array of purported cognitive and mental health difficulties that cast doubt on his fitness to stand trial… Due to difficulties by defence counsel obtaining instructions from the defendant, counsel raised the issue of fitness to stand trial. Accordingly, assessments were ordered by the Court pursuant to Section 38 of the Criminal Procedure (Mentally Impaired Persons) Act 2003 (CPMIPA)” (p. 3). 

"Expert Witness 1 – Clinical Psychologist" stated that the defendant displayed "a highly unusual presentation, strong evidence of feigning both mental health issues and cognitive impairment but that his behaviour could not be explained by malingering alone (considered, in part, to reflect a cultural expression of trauma)... Expert Witness 2 – Psychiatrist" opined that "the defendant exhibited a dubious clinical presentation, but mental health difficulties (e.g. psychosis) could not be ruled out" and ultimately "opined that the defendant was, on balance, unfit to stand trial" (p. 4). 

However, additional assessments by Expert Witness 3 (the first author of the paper) utilized symptom validity tests (SVTs) and performance validity tests (PVTs), revealing that "the defendant’s results were significantly above the empirical cut-offs on the MENT and were also significantly below statistical chance probability” (p. 5).

"The probability that he would obtain 4 or fewer correct answers out of 24 was p(X ≤ 4) = .0008; in other words, assuming no ability regarding autobiographical memory, one would expect this score to occur 8 times in 10,000 occasions… Ultimately, the High Court determined that the defendant was ‘not suffering from any mental impairment which would preclude [him] from facing trial’ R v Malik [2015] NZHC 466 para 18” (p. 9). 

“We provide some recommendations for forensic professionals:

1. Assessors should always consider the possibility of feigning, invalid responding, exaggeration, and/or malingering in every evaluation. Accordingly, they should routinely use well-validated SVTs and PVTs, appropriate to the contextual factors of the case. This will involve the use of specialised and embedded tools, interspersed throughout the assessment. Individually tailored FC measures may be devised and used in specific circumstances (e.g. unsophisticated feigning).

2. Assessors should not rely on clinical judgement and intuition. The assessment of validity should involve multi-factorial and converging lines of robust clinical data (including interview, observed behaviour, and clinical test data). The framework in Sherman et al. (2020) provides guidance on how patterns of symptoms align with accepted models of mental health presentations and cognitive impairment (such as onset, course, and patterns). It also provides guidance on issues such as the number of SVT and PVT failures that may be necessary and issues such as false positive and false negative validity conclusions.
3. Validity assessment should be suited to the clinical phenomena under investigation, the potential clinical population, and the context. In some cases, tests of both symptom validity and performance validity may be required. Even so, invalid responding should not be crossinferred. For example, an examinee may be motivated to demonstrate mental health difficulty but not cognitive impairment, or vice versa.

4. Response bias, exaggeration, or, indeed, malingering does not preclude the presence of genuine or even significant impairment. This includes the co-existence of psychological disorders such as somatic symptom disorder, conversion disorder, and factitious disorder.

5. Assessors should be mindful of test security. Clients may learn about validity assessment and the nature of mental impairments through being coached by others or obtain information via the internet. This necessitates the careful guarding of empirical cut-offs and descriptions of test paradigms.
6. It is appropriate and necessary to encourage clients to always give their best effort and to respond genuinely and honestly. It is even necessary to warn clients that the validity of performance and selfreport will be examined; however, this should not extend to warning of specialised tests, since this can lower the sensitivity of specialised tests and likely does not deter exaggeration, feigning, or response bias. The approach taken should balance informed consent and test security.

7. The assessment of response bias/invalid responding should always consider cultural aspects of behaviour and expressions of distress. The appropriateness of any psychological or neuropsychological tool should be weighed up in relation to ethnicity, culture, language, and acculturation. It is widely accepted that validity tests that have  validated in a majority culture may not be valid with a minority culture.
8. Finally, it is important to be mindful that the key purpose of specialised tests should be to assess the validity of the data gathered. Pejorative terms, such as malingerer (which implies a relatively fixed character trait), should be avoided, as opposed to a contextual and behavioural description such as feigning (behavioural state). Even so, assessors should state conclusions about performance and symptom validity explicitly and clearly. Assessors should engage in ongoing professional development and self-reflection to minimise bias" (p. 12 -13). 

• Below-chance Performance as a "Smoking Gun": "Binder and Chafetz (2018) characterized below-chance performance as ‘the smoking gun of intent’ and incontrovertible evidence of an intention to appear impaired" (p. 2). 
• Legal and Ethical Considerations: The study discusses the implications of malingering in legal contexts, where false positives and false negatives can lead to severe consequences. "False positives may also lead to therapeutic detention in mental health and care facilities that could exceed the duration and liberty restrictions that even a post-conviction sentence may impose” (p. 11).
• Use of Tailored Tests in Court Proceedings: The study describes how the results were received by the Court and how forensic testimony shaped the final ruling. "At a fitness to stand trial hearing at Auckland High Court, the Court heard from four experts, two of whom changed their opinions on fitness over time" (p. 9). 
• Dichotomy in Expert Opinions: The study highlights discrepancies among expert witnesses, emphasizing that some “opined that the defendant remained unfit” while others relied on validity testing to conclude he was malingering. This reinforces the need for standardized criteria to avoid subjective biases (p. 9).