As a Forensic Psychologist, How Should I Decide When the MacArthur Competence Assessment Tool (MacCAT) for Criminal Adjudication Is Appropriate for Use in Criminal Court?

The MacCAT-CA is a 22-item structured interview developed through the MacArthur Foundation Research Network on Mental Health and the Law. It assesses three competence-related abilities derived from the Dusky Standard: Understanding (factual understanding of the legal system and adjudication process), Reasoning (the ability to weigh relevant information and reason about legal options such as plea decisions), and Appreciation (the defendant's capacity to apply legal understanding to their own case, including whether beliefs about the proceedings are grounded in reality or shaped by symptoms such as delusions). The same items are presented to every defendant, the scoring criteria are pre-specified, and the resulting scores are anchored to a national normative sample.

The implication for case selection is that the MacCAT-CA works best where its design assumptions hold. It assumes the defendant can sit through a structured interview, engage with a hypothetical vignette, and produce responses that can be scored against established criteria. It was normed on adult defendants and was not designed for individuals with intellectual disability, severe cognitive limitation, or active florid psychosis that prevents engagement with the vignette task. When a defendant matches the design conditions, the instrument produces standardized, defensible data on the capacities the court cares about. When the defendant does not, the instrument produces either incomplete data or data that misrepresents the underlying impairment. Determining how well the situation matches the instrument is the first key decision the forensic psychologist faces in this process.

The MacCAT-CA adds particular value in cases where competence is ambiguous. A study of forensic mental health evaluators found that participants generally selected collateral records and the unstructured CST interview more frequently than competency assessment tools, with only about half reporting they would use a competency measure in a given case. In contested cases where a defendant is clearly capable or clearly impaired, the instrument is unlikely to change the opinion. In the middle, where the evaluator is weighing partial deficits against partial capacities, the MacCAT-CA's domain-by-domain scoring can isolate which functional ability is impaired and to what degree, which is harder to do narratively.

A useful selection heuristic is to ask whether the structured measure will produce data that the forensic interview cannot. Cases with mixed presentations, intermittent symptoms, defendants with histories of restoration, or referral questions that specifically target reasoning about plea decisions are settings where the MacCAT-CA's Reasoning items often surface deficits that a less structured conversation could miss. The three-domain structure of Understanding, Reasoning, and Appreciation is particularly useful in cases when a defendant performs unevenly across competence-related abilities. A defendant may demonstrate strong factual knowledge of court roles and procedures while showing impaired capacity to weigh the consequences of pleading guilty versus going to trial, or may reason adequately about a hypothetical case while applying that reasoning irrationally to their own circumstances. Domain-specific scores can isolate which functional capacity is impaired and to what degree. Clarity on a defendant's areas of strength and impairment is harder to examine narratively and easier for opposing counsel to contest when offered without standardized support.

The vignette format is also useful when the evaluator wants to separate the defendant's intellectual grasp of legal concepts from the way symptoms (such as paranoid beliefs about the prosecution or grandiose beliefs about the outcome) distort the defendant's behavior in the case. The Appreciation items are specifically designed to surface that distortion, and can help probe whether the defendant can rationally apply their understanding of the court proceedings. A defendant who can accurately describe the role of defense counsel in the abstract but refuses to consult with their attorney because they believe the attorney is part of a conspiracy against them presents precisely the pattern the Appreciation scale targets. The narrative interview can elicit those beliefs, but the MacCAT-CA produces a scored, normed record that quantifies how far the defendant's case-specific reasoning departs from rational application of an otherwise intact knowledge base. The instrument's interpretive ranges (no or minimal, mild, or clinically significant impairment) also give the court a calibrated read on severity rather than a binary judgment, which matters when the legal question is not whether impairment exists but whether it rises to the level that bars adjudication.

By contrast, cases where the referral is essentially a documentation exercise (the defendant is grossly psychotic and unable to track the interview, or the defendant is clearly oriented and articulate about the proceedings) tend to gain little from the additional time. It is worth noting that one study of jail-based competency restoration found that the use of psychological assessment instruments did not significantly reduce the number of contested competency cases. The MacCAT-CA does not necessarily add value in avoiding challenges, but can strengthen a case on the substance.

Several presentations should prompt the forensic psychologist to either supplement the MacCAT-CA with other measures or to forgo it entirely. A practical application study conducted in a public sector forensic setting found that in roughly 30 percent of evaluations, clinical factors, including psychotic or mood symptoms, cognitive limitations, or apparent malingering, contributed to a failure to complete the MacCAT-CA. Active psychosis severe enough to disorganize the defendant's engagement with the vignette is the most common reason for incomplete administration. When the defendant cannot retain or process the vignette, the Understanding and Reasoning items produce floor scores that reflect the administration failure rather than the defendant’s psycholegal capacity. Significant intellectual disability presents a similar concern. The original MacCAT-CA was not normed on this population, and the vignette format can underestimate capacity in defendants who struggle with abstract or hypothetical reasoning but who may nonetheless meet the Dusky criteria as applied to their own concrete situation.

Effort and response style also matter. A defendant suspected of feigning impairment should not be assessed primarily with the MacCAT-CA, because the instrument was not designed to detect feigning and its scores are vulnerable to deliberate underperformance. In these cases, the forensic psychologist should pair the MacCAT-CA with validity testing or with an instrument that incorporates feigning detection, such as the Evaluation of Competency to Stand Trial-Revised, which includes scales designed to assess atypical presentation.

Finally, there are case-level factors that bear on the decision. Charge severity, the specific Dusky prong at issue, the availability of collateral records, and the time pressure of the court's order all shape whether a 45-minute structured interview is the highest-yield use of the evaluator's hour. The MacCAT-CA should be a deliberate addition to an evaluation plan, selected because the case characteristics make it the right tool.

Under the Daubert Standard and Federal Rule of Evidence 702, the methods underlying expert testimony, including the forensic psychologist's choice of instrument, must be reliable and applied appropriately to the facts of the case. The MacCAT-CA's published reliability and validity data, standardized administration, and established place in the peer-reviewed literature all support its admissibility, provided it is used within its empirically supported scope. Administering the MacCAT-CA to a defendant for whom the tool was not normed, or interpreting scores in a way the manual does not support, can convert a strong instrument into a cross-examination liability. The same logic is applied in the APA Specialty Guidelines for Forensic Psychology, which call on forensic psychologists to select methods appropriate to the referral question and that they are qualified to administer and interpret.

Deciding when the MacCAT-CA is appropriate is one of the more consequential judgments a forensic psychologist makes in a competence to stand trial evaluation. The instrument's reliability, its normative base, and its tight mapping onto the Dusky criteria make it a strong choice in cases where the defendant can engage with the structured interview, where competence is ambiguous in ways that domain-specific scores will clarify, and where the legal stakes warrant the additional rigor. It is a poor choice when the defendant's clinical presentation falls outside its design parameters, when feigning is a live concern that the instrument cannot address, or when the referral question is unlikely to be illuminated by what the tool measures. The selection decision is, in the end, a matter of matching the instrument to the case rather than the case to the instrument. Forensic psychologists who make that match deliberately produce evaluations that hold up in criminal court because the choice of method withstands scrutiny.

eBook

• The Criminal Court Expert
  
  

Training

• Limited-Time Discounted Bundle of Three Criminal Court Expert Trainings
  
• Criminal Forensic Assessment Certificate
• Forensic Evaluations
• Identifying and Avoiding “Junk Science” in Forensic Psychological Assessments
• MDLPA: “Folk Psychology,” Heuristics, “Ordinary Common Sense,” & Mental Disability Law
• Evaluations for High Stakes Sentencing: Capital and Juvenile Murder Cases
• Evaluation of Mental State at the Time of the Offense (Insanity/Criminal Responsibility)
• Foundations of Violence Risk Assessment and Management
• Advanced Issues in the Assessment of Risk for Violence: Formulation
• Best Practices in Competency to Stand Trial

Blog Posts

• Ensuring Consistency in Forensic Competency Evaluations
• Use of Psychological Instruments Makes No Difference in Contested Competency Cases
• What Do I, as a Forensic Psychologist, Need to Know About the Daubert Criteria When Preparing Opinions for Criminal Court?
• How Does a Forensic Psychologist Testifying as a Criminal Court Expert Witness Navigate Competency to Stand Trial Evaluations that Hold Up Under Courtroom Scrutiny?