Image © tommaso79
Introduction
Neuropsychologists are frequently invited to report to the court on the extent of an individual’s level of cognitive impairment. The opinion of the neuropsychology expert on the type and extent of cognitive impairment will typically be informed by a range of evidence, including the available medical records, an interview with the claimant, and the results of objective tests of cognitive functioning. A low score on an objective test might indicate a cognitive impairment directly related to the impact of the index event on brain functioning. However, performance on tests of cognitive functioning may be affected by a number of factors, including pre-existing ability level, other aspects of functioning such as sensory or motor ability, medications and so on. The resulting score on a cognitive test may also be a product of how well the individual engaged with the tests. This concept is sometimes referred to as effort but more contemporary terminology favours the concept of performance validity.
Importance of Performance Validity
It is widely recognised, that external incentives in terms of financial rewards, compensation or the avoidance of unwanted scenarios increases the likelihood that cognitive dysfunction will be exaggerated or even fabricated. Behaviour aimed at exaggerating or fabricating cognitive impairments could directly threaten the validity of tests designed to provide objective information about cognitive functioning relevant to a determination of an individual’s underlying level of ability and the impact of an injury that might have affected those abilities, such as from brain damage incurred in the course of an accident.
It is well established that “good practice” in neuropsychological assessment requires the issue of data quality to be addressed and, in particular, includes the testee’s motivation to adhere to the test requirements. According to MacMillan et al 2009 “Motivation that is at variance with test requirements can distort test findings, limit the relevance of the assessment and even invalidate it.”
Malingering or Performance Validity
The latest edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) defines malingering as the intentional production of false or grossly exaggerated physical or psychological symptoms, these being motivated by external incentives including avoidingmilitary duty or work, obtaining financial compensation, evading criminal prosecution, or obtaining drugs. The International Classification of Diseases (ICD-10) also highlights an intentional component, associating malingering with conscious simulation.
However, it is important to recognise that threats to the provision of invalid test data are not limited to deliberate attempts to subvert the assessment process. There may for example be strong psychological factors that can undermine performance validity, including an individual's desire to express distress through their behaviour. In reality, a multitude of factors might affect engagement with cognitive tests, the ‘effort’ put forth, and therefore performance on them. The neuropsychologist will typically consider a number of possible factors including but not limited to pain, fatigue, mood and distress among the possible threats to the extent to which measured performance on a cognitive test can be reliably inferred to represent the true level of underlying cognitive functioning in an individual.
The Assessment Process
The value of any neuropsychological assessment is dependent on the quality of the contributing test data. There are a number of factors that have been known to influence data quality in testing. These include the following:
• The psychometric properties of the test
• The competence of the tester
• Influences affecting the test performance of the testee including identification of sub-optimal effort.
In a medicolegal neuropsychological assessment setting, it is common practice for the individual being assessed to be advised by the examiner that they should try their hardest on the tests being administered. Neuropsychologists will frequently comment on their observations of how the examinee appeared to approach the assessment tasks and note specific behavioural observations that could be relevant in understanding and explaining their presentation. However, we advise caution in the reliance on conclusions that an examinee engaged appropriately with the assessment process and that their performances are a valid reflection of their underlying abilities based solely on the observations of the examiner. It has long been established that clinicians struggle to identify invalid presentations in all cases. Neuropsychologists are not exempt above such difficulties, for example a recent study reported that neuropsychologists would have incorrectly classified 24% of cases without consideration of validity measures. This highlights the need for approaches sensitive to distortions of motivation and underpins the development and use of performance validity tests.
The Development and Use of Performance Validity Measures
Over the last two decades there has been growing interest in the development of methods in which to identify individuals performing below their level of capability such that there are now an array of measures aimed at detecting suboptimal performance. Such tests aim to be highly sensitive and specific, and to be administered relatively easily in a routine clinical situation.
Performance validity tests are typically stand- alone procedures or are embedded in other tests. Such tests aim to detect signs (patterns of test performance) inconsistent with those expected in neurological and psychiatric conditions. The determination of invalid presentations, based on reported symptoms, indicative of deliberate distortion is frequently described as tests of symptom validity. Our focus here is performance validity, though symptom validity may be important in the overall consideration of the claimant’s presentation.
Choice of Performance Validity Test
The requirement that standardised approaches to the consideration of performance validity should be considered by the neuropsychology expert when formulating their opinion is lent support by British Psychology Society (BPS) guidance which specifies that “Effort tests should be given routinely as part of clinical assessment of cognitive function”. A position paper by the National Academy of Neuropsychology (NAN) in the United States goes further, indicating a need for a neuropsychologist “to justify a decision not to assess symptom validity as part of a neuropsychological evaluation.”
Considering such guidance in the context of medicolegal neuropsychology assessments, where the presence of external incentives is well- established and a substantial body of evidence regarding exaggeration of symptoms exists, supports our view that the use of performance validity measures in forensic neuropsychology practice should be considered standard practice. However, exceptions might be argued to exist and careful interpretation of performance on effort tests is required.
There are now in existence a number of independent tests of effort of which some are more commonly applied than others. Recommendations for a particular test is usually dependent on how well established they are in terms of their psychometric properties which include reliability, validity, sensitivity and specificity.
Importance of Sensitivity and Validity
The neuropsychologist should be familiar with published research examining the sensitivity and specificity of the PVTs that they use. Sensitivity in this context refers to the proportion of individuals correctly identified as performing sub-optimally (true positive rate) as opposed to those incorrectly identified as performing sub-optimally (false positives). Whereas test specificity refers to the proportion of individuals correctly identified as not performing sub-optimally (true negatives) as opposed to incorrectly classifying individuals as not performing optimally (false negatives). An important further consideration is how common suboptimal performance is expected to be in a given group, this is referred to as the base rate. It is perhaps unsurprising to find that the base rate of suboptimal performance on cognitive testing in, for example, a group of patients with multiple sclerosis in a clinical assessment setting is much lower than the reported base rate of suboptimal performance in litigating individuals with a mild head injury.
Additionally, different performance characteristics may occur on PVTs depending on individual factors on the person being assessed, including any neurological condition. A familiarity with relevant research conducted on groups of specific individuals can be advantageous in informing the degree of confidence with which the neuropsychologist might place on the PVT results. For example, validation studies of some PVTs have provided different cut-offs in different patient groups, and a number of studies have reported that identification of suboptimal performance can be improved by adjusting conventional PVT cut-offs in individuals presenting following Mild Traumatic Brain Injury.
A consideration of the psychometrics of effort test performances quickly identifies the important considerations that below cut-off performance on a PVT (which may end up reported as failing the effort test) could be a false positive result, and conversely that an above cut-off performance (which may be reported as passing the effort test) may be undetected suboptimal performance i.e. a false negative.
Maximising the Accuracy of Performance Validity Testing
There are a number of approaches available to the neuropsychologist that might enhance the accuracy of their PVT approach and their ability to make a reasoned and robust conclusion about the validity of the obtained test results. These include the following:
Conclusions
In conclusion, effort is recognised as a complex and multifactorial construct. We consider the term performance validity more helpful when forming an opinion on the extent to which the cognitive test data commonly collected as part of a neuropsychological evaluation can be relied upon as representing the true level of underlying functioning for an individual. The assessment of performance validity, and crucially the interpretation of effort tests demands appropriate expertise on the part of the neuropsychologist in order to reliably formulate an individual case and communicate to the Court the basis for and implications of that formulation.
Performance validity testing has evolved rapidly as a field over recent years. A knowledge of relevant current evidence and the ability to synthesize this into assessment procedures and case formulation is in our view a crucial component of contemporary clinical practice when providing expert neuropsychology opinion for the Court. While exceptions may occur, it is our opinion that the availability of performance validity measures, the evidence base regarding their use, and their potential role in providing the Court with evidence regarding the validity or otherwise of obtained cognitive test data, indicates that effort tests should be employed as standard in neuropsychology assessments and that the considerable demands in using them appropriately requires highly developed and appropriate neuropsychological expertise.
Key Points on the Use of Performance Validity Testing:
[1] Cognitivetestresultsarenotvalidifthetestee does not try hard on the tests.
[2] Effort tests should be given routinely as part of clinical assessment of cognitive function.
[3] Therearesomeexceptionswhereroutine assessment of effort is not appropriate. [4] Failure on effort tests requires careful interpretation. Although a number of causes are possible, deceit should always be considered.
[5] Cliniciansshouldbeawareofthesensitivity and specificity of the effort tests that they use and the base rates of sub-optimal performance in the population from which their testee comes and take these factors into account when interpreting findings.
[6] Interpretation of failure on effort tests needs to be reported as clearly as possible.
Published by: