Conventional Folly in Forensic Neuropsychology
- Dr. Ciaran Considine
- Apr 10, 2020
- 4 min read
Given the niche area of practice, it is not uncommon for professionals in both fields referenced by the term "Forensic Neuropsychology" (lawyers/judges and neuropsychologists) to hold particular beliefs that in fact are wrong, or at the very least, not supported by empirical evidence.
Dr. Manfred Greiffenstein outlined 6 common misconceptions in his 2009 paper, "Clinical Myths of Forensic Neuropsychology." I find that even a decade later, they still permeate the area of practice; in fact, I sometimes catch myself walking down the same path. Thus, I thought I would briefly summarize his excellent review here.
‘‘ONLY FIXED BATTERY ADMISSIBLE UNDER DAUBERT’’
Part of the US Supreme Court's ruling in Daubert v. Dow Chemical (1993) included the decision that admissibility of scientific evidence fell under the Federal Rules of Evidence, not the precedent of Frye (1923). In brief, this set the parameters for expert witness opinion based on medical and scientific evidence.
Through no fault of the court, the belief that a fixed battery (i.e., administrating a complete and unedited set of cognitive and sensorimotor tests, regardless of the case) permeated the field; leading to the mistaken perspective that a mixed-flexible battery (i.e., measuring all core domains of neurobehavioral functioning, but selectively picking the tests) would be inadmissible.
This apparently significantly stemmed from mischaracterization of Chapelle v. Ganger, in which the conclusions based on a fixed battery was given more WEIGHT than the flexible battery used by the opposing side. However, both were admissible as expert opinion. Had the neuropsychologist using the flexible battery approach managed to conduct a more thorough assessment, and convince the court of this fact, his/her opinion may have won the day.
"THE ‘PRACTICE EFFECTS' PROHIBITION"
Depending on the particulars of the case, both sides might argue that a plaintiff must not be re-examined within a "protected period" (commonly 6 months), to prevent practice effects from confounding interpretation (e.g., "masking" or "hiding" actual underlying deficits due to improved performance after repeated exposure to tests).
In brief, first, protected periods are not the norm in clinical practice, in fact, practice effects are frequently interpreted. Relatedly, practice effects are not artefact that obscure interpretation, they are reliably unidirectional and empirically characterized in magnitude for most tests/paradigms. Thus, they are integrated into interpretation; indeed, sometimes critical! The absence of a practice effect can in fact be pathological.
"AVERAGE IS THE NEW IMPAIRED"
A common (wrong) argument is that in intellectually gifted individuals, average-range scores can be interpreted to represent a mild decline. Thus, detecting them post-injury represents evidence of associated decline. While most forensic cases do not include a premorbid baseline exam to compare the post-injury results to, we do have plenty of research on what test scores look like for intellectually gifted individuals in general. While individuals with low-to-average range intelligence tend to have a strong relationship between IQ scores and performance in other cognitive domains (e.g., memory, executive functions), this relationship appears to evaporate as IQ crosses into the above-average range - i.e., scores tend to scatter between average and superior range. Thus, an average range score is not in-and-of-itself evidence of post-injury decline for the gifted individual.
"FOREWARNING GUARANTEES MOTIVATION"
Poor effort, disengagement, malingering - all are problematic and routine concerns in the course of forensic neuropsychological assessment. Common practice is to warn the examinee that SPECIFIC performance validity (effort detection) measures are embedded throughout the assessment, and that they will not be distinguishable from the other "actual" measures of cognitive performance.
This myth is based on a research paradigm that is flawed at best, the coached dissimulator, i.e., participants instructed to underperform in a "believable" way. This type of methodology has its use, but to employ it in a study where one group is then warned of the effort detection itself (compared to the other group not receiving warning) leads to a circular roundabout of coaching and un-coaching poor effort. The findings are unlikely to represent litigating examinees who are underperforming their true abilities. Putting aside the methodological flaws, even in this literature there is no clear consensus that warning reduces malingering. If anything, it merely alters the examinee's approach, to become more subtle, and thus harder to detect in examination. Thus, it would seem advisable to encourage full effort, explain the reasoning, but not coach a litigating examinee on the methods used to assess the validity of his or her performance.
"THE MISERABLE MINORITY" in mild TBI
It is common to hear the rule of thumb that 10-15% of mild TBI cases are unrecovered at 1-year post-injury. This falsehood will warrant its own post by myself. First, the estimate appears to be rooted in a study by Rutherford in 1979, who followed 145 mTBI cases for 1 year. While 19 (14.5%) did indeed have neurobehavioral complaints at 1-year, 8 were engaged in lawsuits, 6 showed signs of malingering, and nearly all reported NEW symptoms having evolved between 1.5 months post-injury and 1-year. No control group was used to assess for the base rate of post-concussion symptoms in non-head injured persons (which is quite high, imagine how non-specific headaches, insomnia, trouble concentrating are in the larger population). While 15% indeed were reporting symptoms, there is poor support that this was due to permanent neurological insult due to the mTBI.
Many reviews support the conclusion that mTBI is not associated with permanent brain dysfunction (e.g., Carroll's 2004 review). What *can* be argued in these cases, is that temporary brain dysfunction due to concussion may have remitted, but left in its wake a series of physical and psychiatric complications (e.g., chronic pain, depression, insomnia) that would not likely have evolved in the absence of the injury and subacute (weeks) of brain dysfunction due to concussion.
"EXAMINER BIAS CAUSES POOR EFFORT"
Frequently, invalid performance obtained by opposing counsel's neuropsychologist is explained as the plaintiff reacting ("revolting") against the adversarial nature of an assessment by the defense-selected clinician, rather than attributing the invalid performance sign as concerning for malingering for secondary gain. The story goes that the plaintiff-selected clinician sees the true neurobehavioral status, but the surly and suspicious nature that the plaintiff takes with the defense-selected clinician alters the examination itself (and then would be argued to invalidate it).
The empirical literature is limited (see Greiffenstein's paper, though there is more in the following years), but it actually points to the opposite being true. This makes intuitive sense when considered more closely. A litigant who intends to misrepresent their deficits would presumably exaggerate further under what they view as an amiable and forgiving examiner, but would be more cautious with such behavior in a circumstance with an examiner perceived to be vigilant for such exaggerations (despite presumably attempting to still underperform).
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