Witness Credibility in Regulatory Trials: Research and Practice 2025

VelSafe Insights

Courtroom Conduct and Credibility: What Research and Regulatory Practice Tell Us About Witness Impact

In regulatory trials, expert witness credibility is not a soft variable. Research shows moderate confidence levels consistently outperform high or low confidence in juror ratings. A 2025 MDPI study of 425 participants found that prior attitudes often override expert credentials entirely. Virtual testimony is consistently rated less credible than in-person appearances. And in FDA and OSHA regulatory proceedings, courts have overturned agency decisions specifically for improperly ignoring credible expert input. The 2024 amendment to Federal Rule of Evidence 702 further tightened the standard for expert opinion admissibility. This article compiles current research and regulatory practice on what determines witness credibility and outcome.

Research Through 2025

FDA and OSHA Regulatory Context

Daubert Standard and FRE 702

Nonverbal and Virtual Testimony

425

Participants in a 2025 MDPI study finding that prior juror attitudes toward the insanity defense overrode expert witness credentials in NGRI decisions

MDPI Behavioral Sciences, October 2025

Medium

Confidence level consistently rated highest for credibility by jurors – overly confident and hesitant witnesses both score lower in peer-reviewed research

Journal of AAPL / Expert Institute, 2024

2024

FRE 702 amended to require judges to confirm expert opinions are “more likely than not” based on sufficient facts – raising the admissibility threshold in federal courts

Federal Rules of Evidence / Harvard Law Review, 2025

Expert witnesses in regulatory hearings – before the FDA, OSHA, and the courts that review their decisions – carry weight that extends well beyond the technical content of their testimony. Research consistently shows that jurors and judges evaluate witnesses through multiple lenses simultaneously: the confidence with which testimony is delivered, consistency with documentary evidence, nonverbal behavior, and the setting in which testimony is given. Each of these dimensions is measurable and, increasingly, documentable in peer-reviewed literature.

The legal framework governing expert testimony also shifted materially in 2024. The amended Federal Rule of Evidence 702 requires trial judges to affirmatively confirm – rather than presume – that expert opinions are based on sufficient facts and applied reliably. This change has practical implications for expert preparation in regulatory matters, where FDA and OSHA interpretations may be contested and challenged by opposing experts. Below we compile what the current research and regulatory practice tell us about witness credibility, conduct, and outcome in regulatory proceedings.

Editor's Choice: Key Witness Credibility Findings for 2024-25

58%

of respondents in a large survey agreed that media reporting directly affects the reliability of witness testimony – pre-trial coverage can shift perceptions of both witnesses and the parties calling them. (existing research, VelSafe analysis)

100+

Expert witness engagements handled by The FDA Group across FDA-regulated industries – including drugs, biologics, devices, and GxP environments – reflecting the scale of FDA-related expert testimony in active litigation. (The FDA Group, 2025)

Exception

The Advisory Committee’s notes on the 2000 FRE 702 amendments stated that “rejection of expert testimony is the exception rather than the rule” – but the 2024 amendment shifted this balance by requiring judges to affirmatively confirm reliability. (Harvard Law Review, February 2025)

More likeable

Witnesses who stammer were rated as less confident but more likeable and trustworthy than non-stammering witnesses by mock jurors in a July 2025 study – showing that perceived weakness can paradoxically enhance trustworthiness. (NCBI / British Journal of Psychology, July 2025)

Overturned

Courts have overturned agency decisions – including from EPA, FDA, and OSHA – for improperly ignoring credible expert input. Agencies have discretion, but it is not absolute. (ForensisGroup, 2025, citing Universal Camera Corp. v. NLRB and Motor Vehicle Mfrs. v. State Farm)

Separate

Expert training and experience were found to separately and comparably impact credibility perception in a 2024 study – the first to show these two factors can act independently of each other. (Ferreria and Wingrove, 2024, cited in MDPI 2025)

1. The Confidence Calibration Research: Why Medium Beats High

Low Confidence

Lowest credibility scores. Signals weakness or dishonesty. Jurors interpret hesitation as uncertainty about the truth.

Medium Confidence

Highest credibility scores. Balanced, grounded, considered. Jurors read it as honest expertise rather than performance.

High Confidence

Slightly below medium confidence in credibility ratings. Perceived as overconfident or rehearsed. Risk of “hired gun” label.

A landmark study published in the Journal of the American Academy of Psychiatry and the Law found that moderate levels of manipulated confidence yielded the highest credibility ratings from jurors. Both overly confident and hesitant witnesses were rated as less trustworthy than those presenting at a balanced, measured level. (JAAPL, 2009 – foundational study still cited in Expert Institute 2024 analysis)
The Expert Institute’s 2024 review of this evidence notes that “medium confidence levels resulted in slightly higher credibility rankings than high confidence levels, although both groups scored better than witnesses who appeared to have low confidence.” The practical implication is that witness preparation should aim for grounded authority, not assertive certainty. (Expert Institute, September 2024)
When selecting expert witnesses, counsel should research litigation history carefully. Highly experienced experts may be labeled as “hired guns”, which damages credibility even when their technical qualifications are unimpeachable. Prior cross-examination history is a predictor of how effectively a witness will perform under pressure. (Expert Institute, 2024)
Verbal and nonverbal markers of optimal confidence include: a moderated, stable tone of voice; clarity in speech; moderately paced delivery; willingness to acknowledge uncertainty; smooth narrative statements; good posture; consistent eye contact; and accurate hearing and response. These are trainable behaviors that trial consultants address in witness preparation. (JAAPL, Expert Witness Confidence study)
An unexpected 2025 finding complicates the confidence picture: a study published in the British Journal of Psychology (July 2025) found that witnesses who stammer were rated as less confident but more likeable and trustworthy than non-stammering witnesses by mock jurors. This suggests that perceived effortfulness and authenticity can increase trustworthiness even when delivery fluency is reduced. (NCBI / British Journal of Psychology, July 2025)

2. When Juror Attitudes Override Expert Credentials: 2025 Research

2025 MDPI Study: Expert Knowledge vs. Prior Juror Attitudes (N=425)

Study Design

425 participants read case summaries with expert witnesses assigned high or low knowledge levels. Outcomes measured for NGRI (not guilty by reason of insanity) endorsement and credibility ratings.

Key Finding

Prior attitudes about the insanity defense (measured by IDA-R scale) predicted NGRI endorsement regardless of expert witness testimony. Positive prior attitudes increased NGRI endorsement independently of expert credentials.

Implication

In complex or emotionally charged regulatory cases, jurors may use expert testimony as confirmation of pre-existing views rather than independent evidence. Voir dire and jury selection become as important as expert preparation.

Source: Cain and Smith, MDPI Behavioral Sciences, October 2025 (DOI: 10.3390/bs15101411)

A 2025 study published in MDPI Behavioral Sciences (N=425) found that prior juror attitudes toward the legal defense at issue predicted verdict outcomes regardless of expert witness credentials or testimony content. Jurors with positive prior attitudes toward the insanity defense were significantly more likely to endorse NGRI verdicts even when expert testimony was weak. (Cain and Smith, MDPI, October 2025)
The study confirmed that expert witness education and experience have an influence on credibility perception, and for the first time demonstrated that training and experience can separately and comparably impact juror perception – meaning either factor alone can drive credibility even without the other. (Ferreria and Wingrove, 2024, cited in MDPI 2025)
In complex regulatory hearings – where agency rulemaking, inspection findings, or GMP violations are contested – this research has a direct parallel: decision-makers often arrive with existing mental models of what regulatory compliance looks like. Expert testimony that acknowledges this and addresses it explicitly is more likely to shift perception than testimony that simply presents technical evidence. (regulatory litigation practice; ForensisGroup, 2025)
A 2025 study on inattentional blindness (Taylor and Francis, published May 2025) found that witnesses who failed to notice a crime due to divided attention were rated as less credible even when expert testimony explained the psychological phenomenon. This suggests that certain credibility deficits are difficult to remediate through expert explanation alone. (Tandfonline, May 2025)

3. Nonverbal Behavior and Virtual Testimony: What Reduces Credibility

In-Person: Higher Baseline Credibility

Mock jurors consistently rate in-person witnesses as more eloquent, pleasant, and believable. Even judges report that seeing a witness live affected their credibility judgment in ways video did not replicate.

Virtual: Consistent Credibility Penalty

Video testimony is consistently rated less credible than in-person. Poor lighting, camera angle, technical delays, and flat audio all amplify the credibility gap. Regulatory hearings that moved online during COVID-19 and remained hybrid confirmed this pattern in practice.

Nonverbal Cues That Hurt

Fake smiling, fidgeting, dull vocal tone, poor posture, and inconsistent eye contact all reduce perceived credibility. These effects hold even when the content of testimony is technically accurate.

Research consistently finds that video testimony is rated less credible than in-person appearances. Mock jurors find in-person witnesses more eloquent, pleasant, and believable, and judges have reported that live observation changed their views on credibility in ways that video did not allow. (existing witness credibility research)
For FDA and OSHA regulatory proceedings, which have increasingly used remote or hybrid formats, the practical implication is that expert witnesses appearing by video link should invest additional preparation time in camera placement, lighting, audio quality, and background presentation – each of which affects perceived professionalism and trust. (regulatory practice; witness preparation standards)
Genuine smiling, upright posture, and clear vocal tone add to the sense that a witness is telling the truth, while fake smiles, fidgeting, or flat tone reduce that impression. Research shows these subtle signals often determine whether a witness is perceived as genuine or deceptive, even when the factual content is identical. (JAAPL credibility studies)
The three primary drivers of expert witness perceived credibility are consistently identified as: knowledge, trustworthiness, and likability. A study found that likeability was significantly related to jurors’ perception of trustworthiness but not directly to knowledge or to sentencing decisions – meaning a highly likeable but technically thin expert can appear trustworthy without being persuasive on the merits. (JAAPL, Credibility in the Courtroom, 2009)
An important cross-gender finding: the likeability study of 210 mock jurors also examined the effects of juror gender on expert witness perception, finding that juror extroversion positively predicted credibility ratings across both genders, suggesting that advocate-style witnesses may be rated more highly by extroverted jurors regardless of content. (JAAPL, 2009)

4. Federal Rule of Evidence 702 Amended in 2024: What Changed for Regulatory Expert Testimony

FRE 702 Expert Testimony Admissibility: Pre-2024 vs. Post-2024 Amendment

Core Standard

Expert testimony requires: (1) sufficient facts or data; (2) reliable principles and methods; (3) reliable application to case facts. Judges act as gatekeepers.

Pre-2024

Advisory Committee notes stated “rejection of expert testimony is the exception rather than the rule.” Courts had some latitude to presume reliability and admit testimony with reservations addressed in cross-examination.

2024 Amendment

Courts must now affirmatively confirm – rather than presume – that an expert’s opinion is “more likely than not” based on sufficient facts and reliably applied. The threshold for admissibility is now explicitly confirmed rather than presumed.

Regulatory Impact

For FDA and OSHA-related litigation, this means expert opinions on regulatory standards, GMP compliance, inspection findings, and product liability must show a clear, documented reasoning chain from data to conclusion – not just credentials and conclusions.

Source: Harvard Law Review, February 2025; LII / Cornell Law, FRE 702; ForensisGroup, 2025

The Daubert standard, established in Daubert v. Merrell Dow Pharmaceuticals (1993), places the responsibility on trial judges to act as “gatekeepers” of scientific evidence, evaluating methodology and reasoning rather than simply accepting credentials or reputation. It was extended to non-scientific expert testimony in Kumho Tire Co. v. Carmichael (1999). (LII Cornell Law; ForensisGroup, 2025)
The 2024 amendment to Federal Rule of Evidence 702 tightened the admissibility standard by requiring courts to affirmatively confirm that an expert’s opinion is “more likely than not” based on sufficient facts and methods reliably applied – shifting from presumption of reliability to confirmed reliability. (Harvard Law Review, February 2025)
The practical consequence in regulatory litigation: unsupported conclusions – where an expert states a result without clearly explaining the reasoning path – are now a primary ground for exclusion under the post-2024 FRE 702 framework. An analytical gap between the data relied on and the conclusion offered is also an exclusion risk under the Joiner decision (522 U.S. 136). (ForensisGroup, 2025; Harvard Law Review, 2025)
For FDA and OSHA-related expert testimony specifically, this means experts must be prepared to explain not only what the applicable regulation requires, but how the facts of the case map onto that requirement. Regulatory expertise without case-specific application is increasingly at risk of exclusion under the amended standard. (ForensisGroup, 2025; ICLG Drug and Medical Device Litigation Report, 2025)
In regulatory agency proceedings (as distinct from federal court), agencies like the FDA and OSHA have administrative discretion to accept or reject expert input, but courts have overturned agency decisions for improperly ignoring credible expert testimony. The leading cases include Universal Camera Corp. v. NLRB (340 U.S. 474, 1951) and Motor Vehicle Manufacturers Ass’n v. State Farm (463 U.S. 29, 1983). (ForensisGroup, 2025)

5. Expert Testimony in FDA and OSHA Regulatory Proceedings: What Distinguishes Effective Witnesses

FDA Regulatory Expert Profile

Most effective FDA expert witnesses combine insider regulatory knowledge with clear lay communication skills. Former FDA reviewers, inspectors, and compliance officers are particularly valued for their ability to explain what FDA would have expected – not just what the regulation says.

Multi-Expert Complexity

FDA drug and device litigation typically involves multiple experts reviewing the same facts through different lenses: regulatory affairs experts, engineers, pharmacists, chemists, physicians, and epidemiologists. Coordination of consistent, non-contradictory expert narratives is itself a credibility challenge.

OSHA Safety Expert Profile

OSHA expert witnesses provide fact-based analysis on regulatory standards in workplace injury, fatality, and regulatory dispute litigation. Effective OSHA experts combine standards knowledge with ability to explain industry practice norms – what a reasonable employer in the same industry would have done.

ProPharma’s FDA expert witness team – described as the largest team of former FDA professionals in any consulting firm, including former reviewers, inspectors, compliance officers, and division directors – emphasizes that FDA regulatory litigation often turns on understanding what FDA would have expected, not just what the written standard requires. Credibility in this context is inseparable from demonstrated insider understanding. (ProPharma Group, 2025)
FDA drug and medical device litigation routinely involves multi-expert panels: regulatory affairs experts, engineers, pharmacists, chemists, epidemiologists, and physicians reviewing the same manufacturing records, adverse event reports, and compliance data from different professional perspectives. Each expert’s credibility affects the overall case narrative. (ICLG Drug and Medical Device Litigation Report, April 2025)
Epidemiologists are specifically retained in FDA product liability cases to evaluate MAUDE adverse event database records, FAERS data, and clinical literature – assessing whether reported events, taken collectively, suggest a product defect or alternative causation. The quality of their testimony depends heavily on their ability to explain relative risk and statistical significance to non-specialist triers of fact. (ICLG, April 2025)
OSHA safety expert witnesses in workplace injury and fatality litigation must be able to interpret cited violations, inspection findings, hazard assessments, and industry practice standards in terms that demonstrate both technical knowledge and practical relevance to the specific incident. (LegacyMark Safety, April 2026)
In FDA regulatory proceedings, OPDP (Office of Prescription Drug Promotion) enforcement and off-label promotion cases often involve expert witnesses addressing both the scientific validity of promotional claims and the regulatory standards for fair balance and substantiation – a dual-expertise requirement that narrows the available witness pool and raises the stakes for credibility. (ProPharma Group expert witness services, 2025)

6. Consistency, Media Influence, and External Credibility Threats

Too consistent: raises rehearsal suspicion

Inconsistency with documents: fatal

Media coverage shapes perceptions pre-trial

False memory undermines recollection testimony

Cross-examination exploits discrepancies

Regulatory tribunals and courts rely heavily on how well a witness’s testimony aligns with external evidence – records, documents, inspection reports, and other witnesses. Witnesses who seem overly polished or whose accounts are identical-sounding across multiple persons raise rehearsal suspicions that undermine the perceived spontaneity of their testimony. Consistency must be natural and document-supported. (witness credibility research; litigation practice)
Inconsistency with documentary evidence is the most damaging credibility failure in regulatory proceedings. When a witness’s account contradicts written records, batch documents, inspection logs, or prior statements, cross-examiners will exploit the gap systematically. In FDA proceedings especially, where documentation trails are extensive, inconsistency is rarely recoverable once exposed. (regulatory litigation practice)
58% of respondents in survey research agreed that media reporting directly affects the perceived reliability of witness testimony. In high-profile regulatory cases – product liability matters, mass tort litigation, or FDA enforcement actions – pre-trial media coverage can establish a credibility narrative before a witness takes the stand. (survey data)
Research on memory reliability has found that when jurors believe witness memory is unreliable, they are less likely to convict or rule favorably based solely on witness statements, even expert ones. This creates a credibility gap particularly in cases that rely on recollection of events that occurred years before the proceeding – a common pattern in occupational disease and long-latency toxic exposure litigation. (witness credibility research)
The 2022 Johnny Depp-Amber Heard trial provided a documented case study of expert psychiatric testimony effects at scale: a 2025 study (British Journal of Psychiatry) found that viewing cross-examination clips affected viewers’ attitudes toward the mental health of both parties, demonstrating that expert witness performance in high-profile cases can shape broader public attitudes toward credibility issues beyond the immediate proceeding. (British Journal of Psychiatry Bulletin, February 2025)

Key Takeaways for Legal Teams and Regulatory Affairs Professionals

Aim for medium confidence, not maximum confidence

Peer-reviewed research consistently shows that moderate confidence yields higher credibility ratings than high or low confidence. Witness preparation should calibrate for grounded authority rather than assertive certainty. Overly confident witnesses trigger skepticism; hesitant ones signal weakness. The optimal register is considered, specific, and willing to acknowledge the limits of the evidence.

FRE 702 now requires a confirmed reasoning chain, not presumed reliability

The 2024 amendment requires courts to affirmatively confirm – not presume – that expert opinions are based on sufficient facts and reliably applied. For FDA and OSHA cases, this means expert reports and testimony must explicitly map from the data to the regulatory conclusion, with no assumed inferential steps. Unsupported conclusions are now the primary exclusion trigger under post-2024 FRE 702.

Juror pre-existing attitudes may outweigh expert content

The 2025 MDPI study of 425 participants found prior attitudes predicted outcomes regardless of expert credentials. In regulatory proceedings with strong public or institutional biases – product liability cases with media coverage, agency enforcement matters with established narratives – expert testimony may function as confirmation rather than persuasion. Framing and voir dire strategy should account for this.

Virtual testimony carries a credibility penalty – invest in the setup

Research consistently finds video testimony is rated less credible than in-person. In post-COVID hybrid regulatory proceedings, expert witnesses testifying remotely must compensate through camera placement, lighting, audio quality, and background – factors that directly affect perceived professionalism. The technical setup is now part of witness preparation, not an afterthought.

Document-testimony consistency is non-negotiable in regulatory settings

FDA and OSHA proceedings are document-intensive by nature. Any discrepancy between expert testimony and written records, inspection logs, batch documentation, or prior statements will be identified and exploited in cross-examination. Consistency preparation is as important as content preparation for regulatory expert witnesses.

Agencies can reject expert input – but courts have overturned them for it

FDA and OSHA have administrative discretion over expert input, but that discretion is not absolute. Courts have overturned agency decisions for improperly ignoring credible expert testimony under Universal Camera Corp. v. NLRB and Motor Vehicle Manufacturers v. State Farm. Properly preserving expert evidence in the administrative record is essential for subsequent judicial review.

Sources

Research Studies (Peer-Reviewed)

Legal and Regulatory Sources