Malingering Probability Scale

The Malingering Probability Scale (MPS) was developed in the mid-1990s as a self-report instrument to estimate the probability of malingering, taking account of base rates in underlying populations. The instrument was based on three premises: (1) that psychopathology expresses itself in clearly defined syndromes for which certain symptoms, though perhaps plausibly related, have very low likelihoods of occurrence; (2) that patients will vary in the type of symptoms they feign depending on the context; and (3) that the identification of probabilities of any given individual of malingering should be adjusted according to the base rate of malingering in the population from which he or she was drawn. The MPS was developed by Leigh Silverton, who also designed and conducted many studies; analyzed much of the data; and, in collaboration with Chris Gruber, wrote the MPS manual.

At the time the MPS was developed, there were no other instruments of malingering that provided sensitivity or specificity studies or gave probabilities of malingering predicated on estimates of base rates in the population from which the patient was drawn. The F scale of the Minnesota Multiphasic Personality Inventory (MMPI), which was most widely used, did not distinguish a true-focused response set or random responding. In constructing the MPS, Silverton also tried to address a different type of feigned psychopathology than had been traditionally covered. Past instruments in wide usage had focused on bizarre and psychotic symptoms. Psychotic symptoms tend to be feigned in criminal contexts in which punishment for mentally competent persons judged responsible for their crimes is more aversive than incarceration in a mental hospital. The focus of the MPS is broader, comprising both psychotic symptoms and nonpsychotic symptoms of the type that might be feigned in civil contexts.

Civil litigants should be more apt to feign traumarelated symptoms such as those associated with posttraumatic stress disorder, depression, and dissociation. In civil cases, where money damages are the remedy for a psychological injury, an experienced attorney understands that certain disorders are most likely to stem from trauma and thus yield the highest rewards. Whether through honest questioning by a personal injury attorney attempting to explore damages, through outright coaching, or by self-study of diagnostic material, a litigant may obtain an impression, if not a textbook definition, of the trauma-related syndrome that he or she should emulate to maximize rewards. In such a case, a patient may avoid endorsing bizarre delusional or hallucinatory symptoms represented by the F scale of MMPI–2 or the M test but may endorse posttraumatic stress-like symptoms.

The pseudoclinical items of the MPS cover symptoms related to trauma as well as those related to psychotic phenomena as might be feigned in a criminal context. The symptoms might appear, to the sophisticated faker, to reflect depression, dissociation, posttraumatic disorder, and schizophrenia. Silverton wrote items that seemed, based on the literature and her clinical experience, to reflect genuine psychopathology and those that would appear to reflect genuine psychopathology but did not. One such pair of items for the depression scale is as follows: “I am rarely awakened by sad dreams” F (pseudoitem) and “I sleep well” F (actual item). Depressed people tend to have trouble sleeping and may have sad dreams but are rarely awakened by them. Items such as these were derived rationally and then validated to arrive at a 139-item instrument to detect malingering.

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