Miller Forensic Assessment of Symptoms Test (M-FAST)

The Miller Forensic Assessment of Symptoms Test (M-FAST) is a screening measure for the detection of feigned, or malingered, mental illness. The M-FAST may be used in psychological evaluations of an adult who might be attempting to fake a psychiatric disorder. Because of the reported prevalence of malingering and difficulty of accurate detection through clinical judgment, many researchers and clinicians have suggested routine formal assessment of malingering in most evaluations. Although there are other, more lengthy, assessment measures for malingering detection, the M-FAST was developed to provide the evaluator with a brief screening tool.

Psychologists are often asked to provide an evaluation of criminal defendants to determine if they are competent to stand trial (CST) or to evaluate defendants pleading not guilty by reason of insanity (NGRI). Although most individuals who are found not CST or NGRI do have a severe mental illness, a percentage will attempt to fake mental illness for trial postponement or to be sent to a hospital rather than prison. There are other evaluations, such as disability assessments or psychological evaluations with correctional inmates, where malingering is routinely assessed. In these types of evaluations, malingering is often formally assessed with an instrument developed specifically to detect the faking of mental illness. The M-FAST is often used in these evaluations to screen the individual being evaluated for malingering. If malingering is suggested by the M-FAST results, further evaluation of feigning is carried out.

M-FAST Description and Structure

The M-FAST is a 25-item structured interview that can be administered in approximately 5 to 10 minutes. The measure may be more viable than other instruments in several situations because of its interview format (e.g., reading level of the test taker is irrelevant) and its brief administration time. The M-FAST items were developed to represent the following response styles/ strategies that have been validated for identifying malingered psychiatric symptoms: Reported versus Observed Symptoms, Extreme Symptoms, Rare Combinations, Unusual Hallucinations, Unusual Symptom Course, Negative Image, and Suggestibility. The M-FAST includes items that represent these detection strategies along with items that reflect actual symptoms of mental illness.

Since the M-FAST items were developed to operationally measure several strategies for malingering detection, the factor structure has been examined. Two principal component analyses were performed on the nonclinical and clinical M-FAST development samples. Examination of the scree plots suggested one primary “malingering” factor in both samples accounting for 55% (nonclinical) and 49% (clinical) of the variance. The factor structure of the M-FAST has been tested independently from the development samples by exploratory and confirmatory factor analysis. Similar to the initial factor findings, the latest analyses indicate that the M-FAST is found best to represent a single, dominant factor.

M-FAST Reliability

The M-FAST was developed at a forensic hospital with patients who were either found NGRI or incompetent to stand trial. The initial reliability (or consistency) of the M-FAST was assessed in several ways. The test-retest reliability, given an average of 2 weeks apart, and the internal consistency of M-FAST items were both reported to be high at .92. A third analysis assessed interrater reliability by comparing scores of different M-FAST interview raters. An interclass correlation coefficient, using two-way random effects model with consistency reported, was calculated and found to be high at 99.6. Several independent studies since the development of the M-FAST have indicated that the M-FAST is highly reliability; M-FAST internal consistency ranging from .90 to .92, scale (or strategy) internal consistency ranging from .53 to .82, and interrater reliability found to be 1.0.

M-FAST Validity

The primary goal for M-FAST validation was to demonstrate criterion, convergent, and discriminant validity of the instrument. The diagnostic efficacy of the M-FAST for identifying malingered mental illness was also examined. Initial validation of the measure was demonstrated by significant, positive relationships found between the M-FAST and other validated instruments and scales designed to assess for response style and/or malingered mental illness. These initial studies included forensic patients who were incompetent to stand trial or NGRI and a group of civil outpatients being evaluated for mental illness disability status. In all the samples the M-FAST effectively discriminated between bona fide psychiatric patients and those who were found to be faking mental illness for secondary gain.

Since its development, the M-FAST has been examined for validity and diagnostic efficacy with several different samples including civil psychiatric inpatients, imprisoned offenders being assessed for psychiatric services, and additional samples of forensic inpatients being assessed for CST. In all these samples, the M-FAST was found to be valid and to effectively differentiate those individuals who were malingering from those who were bona fide psychiatric patients. The use of the M-FAST to detect diagnostic-specific malingering has also been examined. In these studies, the M-FAST has been found to be an effective screen when an individual is attempting to malinger the specific disorders of posttraumatic stress disorder, schizophrenia, major depressive disorder, and bipolar disorder.


  1. Guy, L. S., & Miller, H. A. (2004). Screening for malingered psychopathology in a correctional setting: Utility of the Miller-Forensic of Symptoms Test (M-FAST). Criminal Justice and Behavior, 31(6), 695-716.
  2. Jackson, R. L., Rogers, R., & Sewell, K. W. (2005). Forensic applications of the Miller Forensic Assessment of Symptoms Test (M-FAST): Screening for feigned disorders in competency to stand trial evaluations. Law and Human Behavior, 29(2), 199-210.
  3. Miller, H. A. (2001). The Miller Forensic of Symptoms Test (M-FAST) professional manual. Odessa, FL: Psychological Assessment Resources.
  4. Miller, H. A. (2005). The Miller Forensic Assessment of Symptoms Test (M-FAST): Test generalizability and utility across race, literacy, and clinical opinion. Criminal Justice and Behavior, 32(6), 591-611.

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