What Do I, as a Forensic Psychologist, Need to Know About the Daubert Criteria When Preparing Opinions for Criminal Court?

To understand Daubert’s significance, it is essential to understand what it replaced. For much of the twentieth century, expert testimony was governed by the Frye standard, which asked a single question: was the method “generally accepted” within the relevant scientific community? While simple, Frye placed professional consensus above methodological rigor and offered little guidance when science evolved or diverged.

In Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993), the U.S. Supreme Court rejected Frye as the sole test for admissibility in federal courts. The Court held that expert testimony must be both relevant and reliable, and it outlined several non-exclusive factors to help judges evaluate reliability. These include whether a method can be empirically tested, whether it has been peer-reviewed, whether error rates are known, and whether it is generally accepted within the scientific community.

For forensic psychologists, this shift fundamentally changes what courts expect. Testimony is no longer evaluated primarily on the basis of credentials or professional norms. Courts expect experts to articulate the reasoning process that connects data to conclusions and to demonstrate that this reasoning rests on scientifically grounded methods rather than personal judgment alone.

Importantly, Daubert does not require perfection or unanimity. Courts recognize that forensic psychology involves judgment and uncertainty. What Daubert requires is reasoned reliability—that opinions are grounded in methods that can be examined, challenged, and explained. A forensic opinion that cannot be articulated beyond “this is my clinical judgment” is increasingly vulnerable under Daubert scrutiny.

In practice, Daubert is rarely applied as a checklist. Courts do not require forensic psychologists to formally satisfy each factor in isolation. Instead, judges evaluate whether an opinion reflects disciplined reasoning grounded in reliable principles. This evaluation often focuses on how methods are used rather than which methods are chosen. Courts examine whether assessment tools were administered and interpreted as intended, whether interpretations align with the empirical literature, whether conclusions logically follow from the data, and whether alternative explanations were meaningfully considered.

For example, two experts may use the same risk assessment instrument and reach different conclusions. Under Daubert, the admissibility question is not which conclusion is “correct,” but whether each expert applied the tool consistently with its research base, acknowledged its limitations, and explained how conclusions were derived. An opinion that selectively cites scores while ignoring contradictory data is far more vulnerable than one that transparently addresses ambiguity.

This situation is where forensic case formulation becomes critical. Courts are increasingly attentive to whether opinions reflect an integrated analysis of multiple data sources rather than a test-driven or intuition-driven conclusion. Daubert scrutiny often exposes opinions that rely heavily on impressionistic judgment without sufficient methodological scaffolding.

In short, Daubert pushes forensic psychologists toward explainable expertise. The question is not simply “What is your opinion?” but “How did you get there, and why should the court trust that path?”

Under Daubert, judges are charged with acting as gatekeepers for scientific reliability. In theory, this places scientific evaluation “squarely on the shoulders” of the trial court. In practice, research suggests many judges feel underprepared to evaluate core scientific concepts such as falsifiability, error rates, or internal validity.

Studies indicate that judges often admit valid and invalid scientific evidence at similar rates and rarely articulate methodological reasoning when ruling on admissibility. Forensic psychologists cannot assume that strong science will automatically be recognized as such. Instead, reports and testimony must teach the court, clearly explaining how methods work, why they are appropriate, and how conclusions were constrained by the data.

Jurors, by contrast, evaluate forensic evidence through a very different lens. Empirical research consistently shows that jurors rely heavily on an examiner's experience and credentials, often using professional background as a shortcut for evaluating evidentiary strength. Scientific testing, known error rates, and methodological rigor tend to have weaker, less consistent effects on juror decision-making.

In effect, jurors often treat experience as a proxy for accuracy, even though research shows that experience alone is a poor predictor of actual performance. This phenomenon creates a double bind for forensic psychologists: Daubert demands scientific rigor, while jurors may be more influenced by board certification, years of practice, and courtroom demeanor.

Navigating this tension requires strategic communication. Experts must present their professional background without relying on it as a substitute for science. At the same time, they must translate complex methodological concepts into language that jurors can understand without oversimplifying or overstating certainty.

Why Cross-Examination Cannot Substitute for Scientific Rigor
Cross-examination is often described as the greatest engine of truth-finding in the legal system. In theory, adversarial questioning should expose weak methods and unreliable conclusions. Research suggests that cross-examination is often ineffective at helping jurors distinguish between strong and weak science, particularly when the issues are complex. These mock juror studies show that while cross-examination may sensitize jurors to obvious flaws, such as missing data or overt inconsistency, it rarely helps them evaluate subtler issues, such as low reliability, non-blind testing, or construct validity. Jurors often assume that if evidence is admitted at trial, it has already been vetted for validity.

This confusion has important implications for forensic psychologists. Scientific rigor cannot be something that “comes out” on cross-examination. It must be embedded in the evaluation's structure, the report’s logic, and the clarity of direct testimony.

High-stakes evaluations such as competency to stand trial illustrate the ethical weight of Daubert compliance. Competency evaluations are among the most common forensic assessments in the United States, and evaluator opinions are accepted by courts at remarkably high rates. This acceptance places a significant responsibility on the psychologist to use best practices consistently and transparently.

Preparing Daubert-sound opinions requires attention to both tools and process. Psychologists must use instruments with established psychometric properties, understand the legal standards they are addressing, and clearly explain how data were integrated into a coherent case formulation. Selection of tools is important, but disciplined interpretation is even more critical.

Best practices for Daubert-aligned forensic work include actively minimizing cognitive bias through structured decision-making, prioritizing general acceptance when using new technologies, and understanding the limits of inference. Experts should resist the urge to minimize uncertainty in pursuit of clarity. Courts and juries are often more receptive to testimony that demonstrates scientific humility than to testimony that presents polished certainty without acknowledging limitations.

Daubert literacy is also an ethical obligation. Professional standards emphasize empirically grounded assessment, transparency, and sensitivity to cultural and contextual factors. Whether conducting competency evaluations, violence risk assessments, or capital sentencing evaluations, forensic psychologists must ensure that opinions are scientifically defensible, appropriately limited, and clearly reasoned.

Daubert serves as both a gate and a guide for forensic psychological testimony. While courts demand scientific rigor, the realities of judicial literacy and juror decision-making require forensic psychologists to bridge science and communication.

Experts who understand Daubert as a practice framework, rather than a procedural hurdle, are better positioned to produce opinions that withstand adversarial testing. By grounding conclusions in reliable methods, articulating reasoning transparently, and embracing the educator role, forensic psychologists can deliver testimony that is admissible, credible, and ethically sound.

In criminal court, Daubert literacy is not optional. It is foundational to expert-level forensic practice.

Training

• Criminal Forensic Assessment Certificate
  
• Best Practices in Competency to Stand Trial
• AAFP: Ethical and Effective Expert Testimony
  
• Evidenced-Based Forensic Applications of the MMPI-3
• AAFP: The Art and Science of Expert Witness Testimony

Blog Posts

• Is cross-examination an effective means to educate jurors on valid and reliable evidence?
• Support for the Admissibility of Forensic Neuropsychological Evidence
• Experience Trumps Science in Influencing Jurors
• How Do I, as a Forensic Psychologist, Prepare Violence Risk Assessments that Support Expert Testimony in Institutional Settings?