Expert Witness Profiler

Tag: Causation

  • Psychology Expert’s Testimony About PICS Limited

    Psychology Expert’s Testimony About PICS Limited

    Plaintiff Mark Craighead (“Plaintiff” or “Craighead”) brought this wrongful conviction action against Defendants for, among other things, malicious prosecution and coerced confession related to his conviction for the 1997 Murder of Chole Pruett.

    Plaintiff sought damages for mental and emotional injuries allegedly caused by his arrest, interrogation, conviction, and incarceration.

    The Plaintiff disclosed Errol Liverpool, his treating counselor, who treated him for nearly nineteen months and diagnosed him with Post-Traumatic Stress Disorder (PTSD) and adjustment disorder. Defendants retained Dr. Sami Farhat to compile a forensic rebuttal report in which he concluded that he could not substantiate a clear loss of functional impairment or significant psychological injury resulting from Craighead’s wrongful incarceration.

    Dr. Steven Farmilant, Plaintiff’s rebuttal expert, administered a series of diagnostic tests, diagnosed Plaintiff with Complex Post-Traumatic Stress Disorder (CPTSD) and major depressive disorder, and subsequently compiled a surrebuttal expert report in which he concluded that Plaintiff’s diagnoses were attributable to his wrongful incarceration.

    Defendants filed motions to strike the testimony of experts Errol Liverpool and Steven Farmilant while Plaintiff filed a motion to strike the opinions of Defendants’ retained expert, Dr. Sami Farhat.

    Mental Health Expert Witness

    Dr. Errol E. Liverpool has been a licensed professional counselor for many years. He got his Ph.D. in counselor education from an accredited university in 2001.

    Discover more cases with Errol Liverpool as an expert witness by ordering his comprehensive Expert Witness Profile report.

    Psychology Expert Witnesses

    Dr. Steven R. Farmilant received his MA in counseling psychology in 1992 and his doctor of psychology in 1995, and has been a licensed clinical psychologist since 1997. He taught courses at the Adler School of Professional Psychology for 15 years, including courses in trauma and victimology.

    Want to know more about the challenges Steven Farmilant has faced? Get the full details with our Challenge Study report.

    Sami Farhat, Ph.D., is a clinical and forensic psychologist based in the Metro Detroit region of Michigan. Farhat obtained his Ph.D. from the University of Detroit Mercy.

    He completed a postdoctoral fellowship in Forensic Psychology at the Arkansas State Hospital through the University of Arkansas for Medical Sciences (UAMS), where he was subsequently appointed as Assistant Professor of Psychiatry conducting court ordered evaluations and serving as an expert witness. He participated in training and education, including supervising doctoral interns and presenting at the state wide training for community evaluators. During his time with UAMS, he also maintained a part time private practice where he conducted criminal and disability evaluations.

    Gain a comprehensive understanding of Sami Farhat’s qualifications and casework history with his Expert Witness Profile report.

    Discussion by the Court

    A. Errol E. Liverpool

    Defendants argued that Liverpool is not qualified to diagnose PTSD or offer opinions concerning its cause because he is a licensed professional counselor rather than a psychologist, psychiatrist, or forensic clinician; has not published on PTSD or trauma; lacked forensic training; and testified that he was appearing as a treating clinician rather than an expert witness.

    Defendants further challenged the reliability of Liverpool’s PTSD diagnosis because he made it during the first treatment session, did not conduct a structured diagnostic interview or symptom-validity testing, did not review collateral records, and was unfamiliar with certain provisions of the DSM-5-TR.

    The Court found that Liverpool may testify as to Craighead’s PTSD diagnosis and treatment. His opinions regarding his time as Plaintiff’s treating clinician define the scope of his testimony; they do not disqualify him from offering opinions formed during treatment altogether.

    Defendants’ attacks on Liverpool’s PTSD diagnosis go to weight, not Liverpool’s overall qualification to testify as an expert on Craighead’s treatment and PTSD diagnosis, and Defendants are free to challenge its veracity during cross-examination at trial. A treating provider may rely on interviews, reported history, observed symptoms, and the course of treatment in offering opinions.

    The Court further held that it will not prohibit Plaintiff from eliciting Liverpool’s causation opinion attributing Craighead’s PTSD diagnosis to his wrongful incarceration.

    Accordingly, Liverpool may testify that, in his clinical opinion formed during the course of treatment, Plaintiff’s arrest and incarceration caused or contributed to the PTSD and related symptoms he treated. His testimony must remain confined to opinions formed during treatment and based on the clinical history, observations, training, and experience he relied upon in treating Plaintiff; he may not offer causation opinions developed at counsel’s request or from sources extraneous to that treatment.

    B. Sami Farhat

    Plaintiff argued that Farhat relied on incomplete data, offered only a “null” opinion, focused on functional impairment Plaintiff does not claim, and prepared an untimely surrebuttal.

    The Court found that Farhat may offer opinions as to his timely rebuttal report, subject to certain limitations, and that he may not testify as to any opinions offered in his notes critiquing Farmilant’s report.

    With respect to Farhat’s rebuttal report, his interview and record review provide a reasonable basis for an evaluation-specific opinion. Rule 702 does not require an expert to review every available record or contact every collateral witness before offering an opinion. The omitted treatment records and family interviews are proper subjects for cross-examination.

    The Court held that Farhat may describe his examination, the materials he considered, his clinical observations, and his conclusion that the information available to him did not substantiate clinically significant functional impairment or a diagnosable psychological condition. He may not offer the broader opinion that Plaintiff experienced no functional impairment throughout the relevant period or equate the absence of clinically significant impairment during his evaluation with the absence of emotional injury or compensable damages. 

    Plaintiff also sought to exclude a surrebuttal critique prepared by Farhat after reviewing Farmilant’s report. Plaintiff argued that the critique was untimely, exceeded the scope of permissible rebuttal, and introduced new opinions after the expert-disclosure deadlines had passed.

    The Court will not excuse an unauthorized and untimely expert disclosure based on a materially inaccurate account of the discovery record. Accordingly, Farhat may explain and defend the opinions contained in his timely report only. He may not offer any additional opinions first expressed in his notes critiquing Farmilant’s rebuttal.

    C. Steven Farmilant

    Defendants challenged Farmilant’s qualifications, SIMS and PAI analysis, CPTSD diagnosis, and causation opinion.

    The Court found that Farmilant is qualified. He has been a licensed clinical psychologist since 1997, taught trauma and victimology, and provides clinical and forensic trauma services. The absence of board certification, memberships, or publications on the precise subjects affects weight, not qualification.

    The testing disputes also go to weight. Farmilant explained how he integrated recognized instruments with records, interviews, observed behavior, and other indicators, including why the SIMS did not establish malingering and why the PAI coefficient did not support schizophrenia. Defendants may challenge the SIMS-score discrepancy, the supporting literature, the PAI interpretation, and the absence of CAPS-5 or PCL-5 testing; but Rule 702 does not require perfect methodology for expert testimony to be admissible.

    Farmilant may testify to CPTSD. Its absence from the DSM-5 is not dispositive because it appears in the ICD-11 and Farmilant explained the criteria applied.  Plaintiff does not intend to elicit PICS testimony. If it arises, Farmilant may describe Post Incarceration Syndrome (PICS) as a literature-based concept or PTSD subtype, but not as an official DSM-5 or ICD-11 diagnosis. Farmilant’s causation opinion is also admissible. He considered treatment and correctional records, collateral information concerning pre- and post-incarceration functioning, testing, and alternative stressors. Differential etiology requires consideration, not elimination, of every conceivable contributing cause. 

    The weight assigned to particular alternatives is for cross-examination.

    Held

    • The Court granted in part and denied in part the Defendants’ motion to strike the testimony of Dr. Errol Liverpool. Liverpool may testify regarding PTSD diagnosis and treatment, longitudinal observations, Plaintiff’s disclosures and symptoms, causation, and treatment-related trauma concepts. He may not testify concerning adjustment disorder, Farhat’s forensic methodology, or false-confession science.
    • The Court granted in part and denied in part the Plaintiff’s motion to bar Dr. Sami Farhat. Farhat may testify to his timely report subject to the stated limitations but may not offer opinions first expressed in the rebuttal critique.
    • The Court granted in part and denied in part the Defendants’ motion to strike the testimony of Dr. Steven Farmilant. Farmilant may testify regarding his diagnoses, validity testing and malingering analysis, and causation. Any PICS testimony is limited as stated above.

    Key Takeaway

     An expert’s factual foundation must be sufficient for the particular opinion offered, and the Court may prevent an expert from extending a limited dataset beyond what it can reliably support. 

    Please refer to the blog previously published about this case:

    Psychology Expert Allowed to Opine on False Confessions

    Case Details:

    Case Caption:Craighead V. Simon
    Docket Number:2:23cv12243
    Court Name:United States District Court, Michigan Eastern
    Order Date:July 21, 2026
  • Emergency Medicine Expert Not Allowed to Opine on Implicit Bias

    Emergency Medicine Expert Not Allowed to Opine on Implicit Bias

    Following her husband’s death from COVID-19 complications, Plaintiff I’Esha Short (I’Esha) brought this action seeking damages for the medical care he received at the St. Charles County Jail.

    Defendants sought to exclude the testimony of I’Esha’s lone expert, Joel Blackburn, a former medical director at a jail with extensive experience in emergency medicine.

    Emergency Medicine Expert Witness

    Joel M. Blackburn has practiced Emergency Medicine for over 24 years. He was the facility medical director for the emergency department at Capital Region Medical Center in Jefferson City for nearly 2 years during the COVID pandemic. Blackburn has treated hundreds of patients with COVID infection.

    Want to know more about the challenges Joel Blackburn has faced? Get the full details with our Challenge Study report.

    Discussion by the Court

    I. Motion to Exclude Blackburn

    a. Blackburn can testify as to medical causation.

    Defendants offered three main arguments for why Blackburn cannot provide testimony regarding causation. First, they contended that Blackburn lacked relevant expertise. Second, Defendants argued that Blackburn utilized unreliable principles and methods or that he unreliably applied his methodology to the facts. Third, Defendants suggested that Blackburn’s opinions provide little probative value.

    1. Blackburn lacked relevant expertise

    Defendants first argued that Blackburn lacked expertise to testify as to causation. In particular, they emphasize that he “did not practice medicine in a correctional setting during the COVID-19 pandemic,” specialize in various relevant fields, or conduct research into COVID.

    While the fact that he did not practice medicine in a correctional facility during the COVID pandemic may prove fertile ground for cross-examination, it does not override his relevant expertise. As such, Blackburn’s testimony is not excludable on that basis.

    2. Blackburn utilized unreliable principles and methods

    First, Defendants contended that Blackburn failed to consider alternative explanations for Timothy’s death, including his decision to “remain unvaccinated,” his “non compliance with his healthcare needs,” and the “substantial intervening medical care that [he] received at a hospital.”

    However, Blackburn did consider the bulk of the alternative causes that Defendants highlight.

    Second, Defendants contended that Blackburn “cannot reliably conclude under oath that any alleged delay in escalation of care . . . caused Short’s death” because he discounted the possibility that earlier administration of medication could have prevented that outcome.

    While Blackburn opined that earlier administration of the drug alone would not have changed the outcome, he indicated that Timothy needed a combination of interventions and that earlier admission to the hospital would have prevented his death.

    In any event, “an expert’s contradictions or concessions go toward the weight of the evidence put forth by the expert, not toward its admissibility.”

    Third, Defendants claimed that Blackburn offered only impermissible “sooner is better” testimony. In reality, he testified that earlier and more extensive intervention would “more likely than not” have prevented Timothy’s death.

    Finally, Defendants claimed that Blackburn’s testimony is not supported by medical literature. But “while published studies tending to support an expert’s opinion often are a hallmark of admissible testimony, . . . there is no requirement that a medical expert must always cite published studies on general causation.” Thus, Defendants failed to show why Blackburn should be excluded on the basis of unreliable methodology.

    3. Blackburn’s opinions provide little probative value

    Finally, Defendants contended that Blackburn’s testimony is more prejudicial than probative. The Court held that Blackburn’s testimony as to causation is admissible because he has relevant expertise, is sufficiently reliable, and will not create undue prejudice.

    b. Blackburn’s opinions as to implicit bias are excludable under Rule 702.

    Defendants also argued that Blackburn’s testimony regarding implicit bias should be excluded under Rule 702.

    Defendants are right that Blackburn cannot testify as to implicit bias. As an initial matter, it is far from clear how implicit bias testimony would be relevant to the key issues underlying a deliberate-indifference claim, which requires a conscious awareness of a serious medical need.

    More importantly, as the proponent of his opinion, I’Esha “must show by a preponderance of the evidence both that Blackburn is qualified to render the opinion and that the methodology underlying his conclusions is scientifically valid.”

    But Blackburn’s own testimony reveals that, while he lectured in the area of cognitive bias in prison medicine, he is not otherwise qualified in this area.

    c. Blackburn cannot opine on credibility, legal conclusions, or medical bills.

    Defendants also noted that Blackburn impermissibly commented on witness credibility in his report and during his deposition, offered opinions as to legal conclusions, and commented on medical bills.

    I’Esha agreed that Blackburn cannot offer those kinds of opinions.

    II. Motion to Strike Blackburn’s Rebuttal Report

    Defendants asked the Court to strike portions of Blackburn’s rebuttal report addressing the Nurse Defendants, claiming that he should have included these opinions in his initial report.

    But as I’Esha noted, Blackburn added these opinions only after Defendants designated the four nurses as non-retained experts, which happened well after he issued his original report.

    She contended that the rebuttal report does not contain new opinions and, even if so, it would not be procedurally improper.

    Defendants’ arguments fall short for multiple reasons. First, given that they seek a discovery sanction under Rule 37(c), the operative case management order required them to first “file a memorandum requesting a video conference with the Court.” But no such request was made, and Defendants also failed to comply with the Court’s good-faith certification requirement.

    Nor have Defendants even attempted to show good cause for making this request after the discovery-motion deadline.

    The Court held that these procedural deficiencies alone are a sufficient basis for denying relief. But the motion also fails on the merits. After Defendants designated the nurses as experts, I’Esha was free to buttress Blackburn’s opinions to address the expanded categories on which the nurses could testify, and the challenged opinions were limited to the subjects outlined in the nurses’ disclosures.

    Thus, these opinions were timely under Rule 26(a)(2)(D)(ii), and even if they were not, any delay was substantially justified.

    Held

    The Court granted in part and denied in part Defendants’ joint motion to exclude Dr. Joel Blackburn’s testimony and denied Defendants’ joint motion to strike improper portions of Plaintiff’s expert’s rebuttal report.

    Key Takeaway

    There is no requirement for perfect symmetry between an expert’s experience and the precise subject matter of their testimony so long as the expert’s background equips him to help the jury understand the facts or issues in dispute. Blackburn is a board-certified physician with extensive experience treating COVID.

    While Blackburn may lack expertise in some relevant specialties, a doctor’s opinion should not be excluded merely because it involves a field of medicine that he does not specialize in.

    Case Details:

    Case Caption: Short V. St. Charles County
    Docket Number: 4:22cv1117
    Court Name: United States District Court, Missouri Eastern
    Order Date: July 09, 2026
  • Psychiatry Expert Was Not Allowed to Opine on Life Expectancy

    Psychiatry Expert Was Not Allowed to Opine on Life Expectancy

    Plaintiff Brigid “Bridie” Farrell alleged that Defendant Gabel groomed and sexually abused her from June 1997 to January 1998, when she was 15 and Gabel was 33. Plaintiff was a competitive short-track speedskater in the 1990s and 2000s.

    Defendant United States Olympic and Paralympic Committee (“USOPC”) filed a motion to exclude the testimony of Plaintiff’s expert, Dr. Paul Ballas, pursuant to Rule 702 of the Federal Rules of Evidence.

    Psychiatry Expert Witness

    Dr. Paul A. Ballas is a trained psychiatrist with board certifications in child, adolescent, and adult psychiatry.

    Ballas completed an internship, psychiatry residency and child and adolescent psychiatry fellowship at Thomas Jefferson University Hospital in Philadelphia. Ballas has treated over 1,000 children and adults with
    psychiatric and mental illness related to sexual abuse.

    Want to know more about the challenges Paul Ballas has faced? Get the full details with our Challenge Study report.

    Discussion by the Court

    Specifically, USOPC requested that the Court exclude Ballas from testifying about the following:

    (1) his causation opinions, namely, that “Farrell experienced the onset of severe psychiatric symptoms following the sexual abuse that occurred from 1997-1998” and that “Farrell developed a depressive disorder in addition to PTSD as a consequence of the serious trauma inflicted upon her by Andy Gable [sic] from 1997-1998.”

    (2) his vocational functioning opinions, namely, that “the sexual and emotional abuse that occurred from 1997-1998 had an impact on Plaintiff’s future ability to function in her employment capacity.”

    (3) his opinions regarding Plaintiff’s past and future medical costs attributable to the alleged abuse.

    A. Defendant USOPC’s motion to exclude parts of Paul Ballas’ expert testimony

    (a) Causation opinion

    Ballas opined that Plaintiff developed psychiatric symptoms because of Defendant Gabel’s alleged abuse. USOPC took issue with this causation opinion, arguing that, “given the lack of any evidence or data suggesting that Plaintiff’s psychiatric symptoms developed immediately after her alleged abuse by Defendant Gabel, Ballas’ opinion that there was a clear demarcation of symptoms before and after the alleged abuse — and thus that the alleged abuse caused Farrell’s psychiatric symptoms and conditions — is speculative and should be excluded.”

    However, the Court found that, even if this was a flaw in Ballas’ reasoning or methodology, this flaw is not “‘large enough that Ballas lacks good grounds for his conclusions.’”

    Moreover, the Court concluded that Ballas’ opinion that, because of a traumatic experience as a child, Plaintiff later in life developed psychiatric conditions that did not exist prior to the traumatic experience is not the type of testimony which “is speculative or conjectural.”

    USOPC also criticized the reliability of Ballas’ report by arguing that his “failure to consider and rule out other likely causes of Plaintiff’s alleged injuries constitutes an independent and additional reason to exclude his causation opinions.”

    However, Ballas did acknowledge other traumas in his report. Ballas explained that, although other traumatic incidents have occurred, the abuse by Defendant Gabel was the first, making it the “index event” in causing Plaintiff’s trauma.

    Ballas also reviewed Farrell’s medical records and medical history, along with the medical records of her treating psychiatrist, Dr. Eleni Maloutas. USOPC took issue with the Ballas’ report to the extent that Ballas relied on Maloutas’ conclusions.  However, an expert’s reliance on a Plaintiff’s treatment record will not bar this expert’s testimony from being admitted. 

    The Court concluded that the methodology that Ballas used to reach his conclusions about the cause of Plaintiff’s psychological injuries is reasonable.

    (b) Ballas’ opinion regarding Plaintiff’s vocational capacity

    Ballas opined that Plaintiff’s “ongoing symptoms are clearly affecting her relationships and vocational functioning.”

    Ballas opined that, “in his opinion, the sexual and emotional abuse that occurred from 1997-1998 had an impact on Plaintiff’s future ability to function in her employment capacity, since her PTSD, anxiety, and depressive symptoms were directly related to this abuse.”

    Ballas, a trained psychiatrist, opined that the severe psychological symptoms Plaintiff is experiencing impacted her ability to function in her career. This application of Ballas’ training and experience does not contain a “flaw in his reasoning or methodology that is large enough that he lacks good ground for his conclusions.”

    Accordingly, the Court found that Ballas’ opinion regarding Plaintiff’s vocational capacity is reliable.

    (c) Ballas’ medical cost opinions

    USOPC contended that, although Ballas purportedly calculated Plaintiff’s medical costs stemming from the alleged abuse, his methods for calculating those costs are unreliable and should not be considered.

    With regard to the issue of past medical costs, Ballas estimates that “the financial cost of Plaintiff’s therapy and psychiatric visits since 2014 was approximately $40,000.”

    In this case, Ballas’ estimate of past medical expenses is not reliable. Plaintiff’s past expenses stemming from the alleged abuse can be calculated with specificity based on her actual treatment records. There is no need for an expert to estimate what those costs were. Furthermore, Ballas’ estimate of past treatment costs is unreliable because it includes costs that Plaintiff never incurred because, during certain periods, she received no treatment and, thus did not incur any costs. Therefore, the Court found that Ballas may not testify about Plaintiff’s past medical costs because any such testimony would be neither reliable nor necessary.

    With regard to future medical expenses, Ballas opined that Plaintiff will require mental health treatment “for at least an additional 40 years.” In this case, Ballas has not provided any information that suggests that he is qualified to testify about an individual’s life expectancy or that he has any actuarial experience. Therefore, the Court found that Ballas lacked the base level qualifications that Rule 702 requires to opine on Plaintiff’s life expectancy.

    Furthermore, the Court found that Ballas is qualified to testify regarding his opinion on Plaintiff’s yearly medical costs. The Court also found that Ballas’ opinion regarding Plaintiff’s future medical costs is relevant because it will assist the trier of fact in calculating any damages to which it concludes Plaintiff is entitled.

    B. Defendant USOPC’s motion to strike Ballas’ May 30, 2024 Declaration

    USOPC contended that the declaration of Ballas that Plaintiff filed in support of her opposition to its motion to exclude Ballas’ testimony contains new opinions asserted after the close of discovery and contains improper legal arguments.

    The Court has reviewed the information contained in Ballas’ May 30, 2024 declaration and finds that it is related to the initial Ballas report. For example, in this declaration, Ballas reaffirms much of what he has already stated or is responding to USOPC’s criticisms of his report. 

    Furthermore, the Court found that USOPC’s argument that Ballas is making improper legal arguments in his May 30, 2024 declaration is without merit. In all the paragraphs that USOPC cited as alleging impermissible legal arguments, no such arguments are made. Rather, Ballas is permissibly responding to the criticisms of his expert report that USOPC made in its motion to exclude those reports.

    Held

    The Court granted in part and denied in part Defendant USOPC’s motion to exclude the expert testimony of Dr. Paul Ballas.

    Key Takeaway

    When determining whether to admit expert testimony, a court must consider the qualifications of an expert to testify as to a particular matter. Ballas has not provided any information that suggests that he is qualified to testify about an individual’s life expectancy.

    Please refer to the blog previously published about this case:

    Psychiatry Expert Allowed to Opine on Psychological Injuries

    Case Details:

    Case Caption: Farrell V. The United States Olympic & Paralympic Committee
    Docket Number: 1:20cv1178
    Court Name: United States District Court, New York Northern
    Order Date: June 22, 2026
  • Emergency Medicine Expert Not Allowed to Opine on Loss of Vision

    Emergency Medicine Expert Not Allowed to Opine on Loss of Vision

    Plaintiff, Amaris I Ward, who was seventeen years old during the events of this case, sought medical treatment at Madigan Army Medical Center (“MAMC”) over several weeks in October 2022.

    Plaintiff alleged that emergency care providers at MAMC failed to properly evaluate and diagnose her with acute bacterial rhinosinusitis on October 16, 2022, which led to their failure to determine the extent of the sinusitis so it could be treated in a timely fashion. As a result, Plaintiff alleged that the bacterial infection progressed untreated for more than 30 hours, which caused permanent damage to the optic nerve in her left eye, resulting in permanent blindness in the left eye. Plaintiff alleged that these actions amounted to a breach of the standard of care of reasonably prudent emergency care providers when confronted with symptoms such as Plaintiff’s.

    Defendants filed a motion to exclude the testimony of Plaintiff’s expert, Dr. Richard O. Cummins.

    Emergency Medicine Expert Witness

    Richard Oliver Cummins is board-certified in both internal medicine and emergency medicine.

    He joined the faculty of the Department of Medicine at the University of Washington in 1981, and was promoted to the rank of full Professor in 1993. As a member of the Department of Emergency Medicine he worked as an attending physician in the UWMC Emergency Department, providing clinical care, supervising medical students and emergency medicine residents in training, as well as providing direct patient care.

    Discover more cases with Richard Cummins as an expert witness by ordering his comprehensive Expert Witness Profile report.

    Discussion by the Court

    1. Cummins is qualified as an expert

    Defendants argued that Cummins did not have the clinical experience or educational basis to anchor his causation opinion about the cause of Plaintiff’s infection.

    The Court noted that Cummins is qualified to testify because he has been medical physician for several decades and is board-certified in both internal and emergency medicine.

    Although he is not an infectious disease specialist, he is a board-certified emergency medicine physician with over 39 years of experience. To the extent there is a challenge to Cummins’ qualifications, the Court is satisfied he has demonstrated at least a “minimal foundation of knowledge, skill, and expertise required” to give expert testimony on the issues in this case.

    2. Cummins’ methodology is not reliable

    Defendants argued that Cummins opined that the failure to start Plaintiff on either levofloxacin or moxifloxacin on October 16, 2026 caused her permanent loss of vision—and argued that this opinion is unreliable.

    According to Cummins, a “causal chain” of failures to comply with the standards of reasonable emergency department care led to Plaintiff’s vision loss. Within the “causal chain” was the failure to timely initiate “appropriate treatment,” otherwise identified as “appropriate intravenous antibiotics.”

    Cummins determined from review of available records that Plaintiff’s left eye blindness was caused by “damage to her optic nerve (optic neuropathy) from her infectious sphenoid sinusitis,” which contained fusobacterium necrophorium. But nowhere in Cummins’ expert report or deposition testimony did he explain why or how the failure to diagnose Plaintiff with severe bacterial pan-sinusitis caused damage to her optic nerve.

    Simply put, the Court cannot identify the generally accepted methodology Cummins used in arriving at his medical conclusions on causation. When asked how he reached the opinion that if physicians had given Plaintiff antibiotics on October, the antibiotics would have been effective to prevent Plaintiff’s vision loss, Cummins stated, “A general experience that antibiotics often work.” To the extent Cummins’ opinions are based on his general experience, he did not explain “how that experience leads to the conclusion reached, why that experience is a sufficient basis for the opinion, and how that experience is reliably applied to the facts.”

    Held

    The Court granted Defendants’ motion to exclude the testimony of Dr. Richard Cummins.

    Key Takeaway

    A medical expert may rely heavily on their experience, but they must still explain their methods. Put differently, the opinion must describe a “methodology that can be challenged in some objective sense” because “a subjective, conclusory approach cannot reasonably be assessed for reliability.”

    Case Details:

    Case Caption: Ward V. United States Of America
    Docket Number: 3:24cv5836
    Court Name: United States District Court, Washington Western
    Order Date: June 12, 2026
  • Chemistry Expert Was Allowed to Opine on Phosphine-Air Mixtures

    Chemistry Expert Was Allowed to Opine on Phosphine-Air Mixtures

    Crestbrook Insurance Company, as subrogee of Central Prairie Co-Op, sued Ecolab, Inc., for negligence and breach of contract.

    This case is about a fire that destroyed a grain storage bin and its contents. Central Prairie is a Kansas grain cooperative that stores wheat and other grains in large bins at facilities across the state. In late October 2022, Ecolab—a commercial fumigation company—fumigated two bins at Central Prairie’s remote, unmanned site in Lyons, Kansas. Seventeen days later, a fire broke out in one of the bins, destroying the wheat inside and damaging the bin.

    Crestbrook, which insured the property, paid Central Prairie $573,919.74 for the loss and, as subrogee, then filed suit, asserting claims for negligence and breach of an oral contract.

    Ecolab’s phosphine product at issue here, VAPORPH3OS, addressed the flammability risk through its delivery system. Ecolab applied VAPORPH3OS using a machine called the HDS 200, which automatically dilutes the raw phosphine with carbon dioxide or forced air. The HDS 200 is engineered to ensure the delivered concentration never exceeds 10,000 parts per million—about 55% of the flammability threshold—and its built-in safeguards are designed to keep the concentration from ever crossing that line.

    Between Crestbrook and Ecolab, the parties have filed four motions to exclude expert testimony. Crestbrook sought to exclude two of Ecolab’s experts, Benjamin Streifel and Jeffrey Tucker while Ecolab sought to exclude two of Crestbrook’s experts, Dirk Maier and Peter Dahl.

    Chemistry Expert Witness

    Benjamin Streifel is a chemist. He trained at Johns Hopkins University and has practiced in the field for more than fifteen years.

    Want to know more about the challenges Benjamin Streifel has faced? Get the full details with our Challenge Study report.

    Entomology Expert Witness

    Jeffrey B. Tucker is a board-certified entomologist with more than forty years of experience in commercial fumigation.

    Discover more cases with  Jeffrey Tucker as an expert witness by ordering his comprehensive Expert Witness Profile report.

    Agricultural Engineering Expert Witness

    Dirk E. Maier is an agricultural engineer. He is a professor in the Agricultural & Biosystems Engineering Department at Iowa State University. Maier as worked with fumigation practices at different institutions for close to thirty years.

    Get the full story on challenges to Dirk Maier’s expert opinions and testimony with an in-depth Challenge Study.

    Fire Investigation Expert Witness

    Peter J. Dahl is a Certified Fire Investigator with decades of experience conducting fire origin and causation analyses.

    Gain a comprehensive understanding of Peter Dahl’s qualifications and casework history with his Expert Witness Profile report.

    Discussion by the Court

    Benjamin Streifel

    Ecolab retained Streifel to address the chemistry, properties, and behavior of phosphine gas and phosphine-air mixtures in confined containers.

    He offered four opinions. First, there is no evidence of phosphine separation or concentration once the HDS 200 mixes phosphine into air. Second, gravitational separation based on density alone, as hypothesized by Crestbrook, would require timescales exceeding the ten-day window between the bins’ unsealing and the fire. Third, gravitational separation at the applied concentrations would require length scales far exceeding Bin 2’s 100-foot height. Fourth, phosphine concentrations in grain bins naturally decrease, rather than increase, over time. Each of these opinions challenged Crestbrook’s core causation theory that residual phosphine could have settled and concentrated in Bin 2’s cone bottom to the level required for ignition.

    Analysis

    Crestbrook argued that Streifel’s opinions exceeded the scope of his expertise. In particular, it argued that his opinions are speculative and rest on unreliable methods because he has not worked with phosphine, performed a commercial fumigation, or formally studied conditions inside a grain bin. Crestbrook failed to explain how or why Streifel’s lack of these experiences undermines the reliability of his analysis or methodology.

    Crestbrook next argued that Streifel conducted no independent investigation and relied “exclusively” on information Ecolab supplied. Streifel reviewed the HDS 200 Operator’s Manual, the Fumigation Management Plan, the VAPORPH3OS product label, depositions from those involved with the fumigation, and forty other sources, including fifteen peer-reviewed publications on phosphine and gas diffusion.

    Crestbrook also argued that Streifel did not engage with the scene investigators, did not attend a scene examination, and did not attend a lab examination. Ecolab noted, and Crestbrook did not deny, that scene investigators photographed and measured the empty bin, electrical equipment, and charred aeration fan. At the lab, they examined the removed fan for signs of fire origin. Crestbrook made no concrete argument why Streifel had to experience this in person and could not rely on the recorded observations.

    Crestbrook’s last set of critiques concerned Streifel’s understanding of the HDS 200 on two grounds. First, Crestbrook argued that Streifel’s opinions were unreliable because they rested on a capability the HDS 200 did not have, namely, the ability to create a “new and stable gas.” But nowhere in his report did Streifel discuss this capability. And when the issue arose during his deposition, Streifel explicitly disavowed Crestbrook’s characterization of his opinion.

    Second, Crestbrook argued that Streifel never inspected the HDS 200, never tested its output, and never reviewed maintenance or calibration records to confirm it operated as designed. But this conflates the issue. Streifel did not opine on whether the HDS 200 worked as intended, and, notably, his analysis took into account malfunction scenarios.

    The Court found that none of Crestbrook’s challenges to Streifel’s opinion show that his opinion must be excluded. 

    Jeffrey Tucker

    Crestbrook sought to strike Tucker’s opinion that the industry standard for commercial fumigators is to follow the EPA label physically attached to or accompanying the pesticide at the time of manufacture, rather than the most recently approved EPA label that may have been issued after manufacture.

    Crestbrook first argued that Tucker’s opinion is “flatly contradicted” by federal and Kansas pesticide statutes. But this is not a basis for exclusion. The gist of Crestbrook’s argument on this point appears to be that because Tucker’s conclusion is wrong, his opinion is inadmissible. That argument failed to justify exclusion because the relevant inquiry is whether an expert’s principles and methods are reliable, not whether the moving party agrees with where those methods lead.

    Crestbrook next argued that Tucker’s opinion is an impermissible legal conclusion that “invades the Court’s role” of instructing the jury on the law.

    The bulk of Tucker’s challenged opinion is permissible. He described the training of fumigators and industry customs. He explained the practical reasons for that custom, namely, because labels do not always reach fumigators promptly after a new one is approved, and product purchased earlier may sit in inventory before use.

    In his deposition, however—the testimony on which Crestbrook’s motion rests—Tucker more than once framed that custom in the language of legal obligation, veering into territory reserved for the court. Pressed by Crestbrook’s counsel, he stated that fumigators “are obligated to follow” the cylinder-affixed label and “are not obligated to follow the most recent EPA label.” Because those statements were elicited at deposition rather than offered as report opinions, the limitation is prophylactic.

    The Court granted Crestbrook’s motion to exclude Tucker’s opinion to the extent that it treated the industry custom he described as a matter of legal obligation or compliance.

    Dirk Maier

    Maier offered an interlocking chain of opinions on causation. Specifically, he asserted that residual phosphine remained in Bin 2 after Ecolab unsealed it on November 1, 2022. Then, over the next ten days, the residual gas settled and concentrated in the bin’s cone bottom under the combined effect of natural convection and a day-night “pumping action” through the headspace. The concentration eventually reached phosphine’s 18,000-parts-per-million lower flammability limit and the gas then self-ignited and initiated a “slow pyrolysis” smoldering fire in the wheat surrounding the north aeration duct.

    Maier also opined that Ecolab’s failures to monitor phosphine concentrations and to aerate Bin 2 upon unsealing constitute “violations of State of Kansas and federal law.” Maier’s causation chain provided the foundation of Crestbrook’s negligence theory by supplying chemistry and physics explanations for how residual phosphine settled and concentrated in Bin 2’s cone bottom to the ignition threshold during the ten-day window before aeration.

    Analysis

    Ecolab challenged Maier’s central causation theory. Specifically, it sought to exclude his opinion that residual phosphine, after Ecolab unsealed Bin 2 on November 1, 2022, settled by gravity and convection into the cone bottom of Bin 2 and concentrated to its 18,000 parts per million lower flammability limit during the ten-day window before aeration.

    To begin with, Maier conducted no testing of the theory. Moreover, Maier admitted that he is aware of no peer-reviewed literature documenting gravitational concentration of phosphine within a grain bin. Furthermore, Maier’s own peer-reviewed work on phosphine, which he omitted from his report, undermined his opinion.

    Ecolab next challenged Maier’s calculation that 2,280 grams of phosphine could reach 18,000 parts per million if concentrated into a volume of 3,165 cubic feet within Bin 2. First, it assumed that all 2,280 grams of phosphine introduced into Bin 2 on October 27 remained in the bin on November 1—an assumption Maier conceded is wrong and that he made no attempt to quantify. Second, the calculation’s premise that the gas was “trapped” or “contained” within a small subset of the bin’s interior—the 3,165 cubic feet of the cone bottom—had no basis in the record.

    Ecolab’s third challenge concerned Maier’s opinion that once phosphine reached its 18,000 parts per million self-ignition limit in the cone bottom of Bin 2, it ignited and initiated a “slow pyrolysis” smoldering fire in the wheat surrounding the north aeration duct.

    Maier admitted that he has done “no calculation, modeling, or testing to determine how much thermal energy would have to be given off by a phosphine gas ignition to in fact ignite wheat.”

    Ecolab’s final challenge concerned Maier’s statements that Ecolab’s failure to monitor and failure to aerate “are violations of State of Kansas and federal law.”

    The Court held that the legal-conclusion problem is properly remedied not by wholesale exclusion of the expert’s testimony but by exclusion of the offending statements. Maier remains free to testify—within the boundaries set above—about what the VAPORPH3OS label requires of a licensed fumigator, the industry custom for monitoring and recording phosphine concentrations during fumigation, the content of the Fumigation Management Plan Ecolab submitted, and the practical reasons that label requires the steps it does.

    Peter Dahl

    Dahl opined that the ignition source was a concentrated pocket of residual phosphine that, having settled at the lowest point in the north aeration pipe inside Bin 2, reached its 18,000-parts-per-million lower flammability limit and produced a momentary flame front that ignited adjacent wheat. Dahl’s specific-causation chain depends on the general-causation premise—that residual phosphine could and did concentrate to ignitable levels in Bin 2’s cone bottom—that he obtained from his conversations with Maier and his review of phosphine manufacturers’ Material Safety Data Sheets. Dahl conducted no independent research, testing, modeling, or peer-reviewed-literature analysis of phosphine settling, concentration, or the ignition mechanism his opinion describes.

    Ecolab argued that Dahl’s causation opinion did not satisfy Rule 702 because it depended entirely on a general-causation premise that Dahl did not himself develop, but instead obtained from Maier.

    The evidence on which Dahl relies for his causation case needs to be independently reliable. But, as noted above, Maier’s opinion as to causation—which forms the basis of Dahl’s own opinion—was not reliable. Without that foundation, Dahl’s causation analysis cannot stand and thus, the Court granted Ecolab’s motion to exclude his testimony.

    Held

    • The Court denied Crestbrook’s motion to exclude Benjamin Streifel.
    • The Court granted in part and denied in part Crestbrook’s motion to exclude Jeffrey Tucker.
    • The Court granted in part and denied in part Ecolab’s motion to exclude Dirk Maier.
    • The Court granted Ecolab’s motion to exclude Peter Dahl.

    Key Takeaway

    • An expert may testify where the subject is within “the reasonable confines” of his expertise even if he lacks specialization in the precise application.
    • While testing is not required, when an expert relies on a novel theory and the basis for the expert’s opinion is subject to debate, the importance of testing as a factor in determining reliability is at its highest.

    Case Details:

    Case Caption: Crestbrook Insurance Company V. Ecolab Inc.
    Docket Number: 6:24cv1091
    Court Name: United States District Court, Kansas
    Order Date: June 11, 2026
  • Roofing Expert’s Causation Opinion Excluded

    Roofing Expert’s Causation Opinion Excluded

    This case arises out of an insurance claim (the “Claim”) Plaintiff Mike Nguyen submitted to Allstate seeking coverage under his homeowners insurance policy (the “Policy”) for damages to the roof and certain exterior components of his dwelling (the “Property”) that he said were caused by a hail storm that occurred on May 1, 2022 (the “Storm”). However, Allstate inspected the Property and alleged that the damages to the steel roof were not covered pursuant to the Metal Roof Surfaces Cosmetic Damage Exclusion Endorsement to the Policy (the “Cosmetic Damage Endorsement”).

    Allstate sought to exclude the testimony of the Plaintiff’s retained experts, Chris Rhynehart and Brandon Allen.

    Roofing Expert Witness

    Chris Rhynehart has served as the owner and operator of Rhynehart Roofing and Construction for over thirty-five years.

    Get the full story on challenges to Chris Rhynehart’s expert opinions and testimony with an in-depth Challenge Study.

    Insurance Expert Witness

    Brandon Benjamin Allen, AIC is a licensed adjuster in Texas and Louisiana with almost twenty years of experience adjusting claims. He also holds credentials
    including an Associate in Claims, and he is a HAAG Certified Roof Inspector, which means he received specialized training to assess roof damage.

    Want to know more about the challenges Brandon Allen has faced? Get the full details with our Challenge Study report.

    Discussion by the Court

    A. Chris Rhynehart

    Allstate argued that Rhynehart’s opinions are irrelevant because he made no attempt to connect the damage to the May 1 storm or any storm that occurred during the Policy period of February 1, 2022 to February 1, 2023.

    Rhynehart’s report said only that the Plaintiff’s property “shows clear signs of a previous severe hail storm,” with multiple areas “indicating significant impact damage.” He made no attempt to connect that damage to the May 1 storm, or to date the damage at all. His report included a weather report showing that a hail storm occurred near the Plaintiff’s property on May 1, 2022, but the same report lists eleven other hail storms that impacted the Plaintiff’s property in the years before the May 1 storm. Rhynehart also failed to consider any possible alternative causes of the damage. Nor did he present any information about the condition of the Plaintiff’s roof before the storm.

    The Plaintiff conceded that Rhynehart’s opinions failed to connect the roof damage to the May 1 storm.

    The Court found that Rhynehart’s expert opinions as to causation are not relevant because they failed to speak to whether the May 1 storm caused the damage that resulted in a leak in the Plaintiff’s roof. It is the Plaintiff’s burden to establish this.

    However, Allstate did not contest Rhynehart’s competence to testify about the overall “condition of the property, the presence of wind and hail damage, the extent of the damage, and to provide an unbiased estimate” as to the cost of repair.

    B. Brandon Allen

    Plaintiff designated Allen as a “testifying expert to contradict or rebut the evidence, opinions, analysis, and expert designations” of Allstate’s retained expert witnesses.

    Allen’s expert report—much like Rhynehart’s report—simply offered a view of the evidence that favored the Plaintiff. The Court found that Allen’s report did not even mention Allstate’s experts, much less attempt to contradict specific findings they made in their reports.

    Allen’s report did not attempt to specifically rebut the findings of Allstate’s experts. But even if it had, his report went far beyond that and offered its own “separate and distinct analysis.”

    Held

    The Court granted in part and denied in part Allstate’s motion to exclude the testimony of Plaintiff’s retained expert witnesses Chris Rhynehart and Brandon Allen.

    Key Takeaway

    A rebuttal expert’s report must relate to the specific findings advanced by the opposing expert, not simply offer a different view of the case.

    Case Details:

    Case Caption: Nguyen V. Allstate Vehicle And Property Insurance Company
    Docket Number: 2:24cv186
    Court Name: United States District Court, Texas Northern
    Order Date: February 23, 2026
  • Maritime Expert Allowed to Opine on Safety Standards

    Maritime Expert Allowed to Opine on Safety Standards

    Plaintiff Jonathan Conner is a Jones Act seaman who worked for REC Marine aboard the M/V GOL Warrior. While working aboard the vessel, he suffered what was later diagnosed as a heart attack at some point in the day on January 27, 2024.

    Conner alleged that REC Marine was negligent in its handling of his medical emergency and that the vessel was unseaworthy because the crew lacked the training and preparation required to respond appropriately to the medical emergency.

    REC Marine filed motions to exclude and/or limit the testimony of two of Plaintiff’s designated experts—Captain Christine Hafen, Plaintiff’s marine liability expert, and Dr. Xianfeng Wen, one of Plaintiff’s treating physicians who is presently designated as a non-retained medical expert pursuant to Rule 26(a)(2)(C) of the Federal Rules of Civil Procedure.

    Maritime Expert Witness

    Captain Christine Hafen possesses over 25 years of experience in maritime and offshore drilling, including roles as a ballast control operator, dynamic positioning operator, captain and chief mate.

    Discover more cases with Christine Hafen as an expert witness by ordering her comprehensive Expert Witness Profile report.

    Cardiovascular Diseases Expert Witness

    Xianfeng Wen earned his medical degree from Shanghai Medical College of Fudan University in Shanghai, China. To begin with, he completed his residency in internal medicine and fellowship in cardiovascular disease at the University of Texas Medical Branch at Galveston where he served as chief fellow.

    Board certified in cardiovascular disease and comprehensive echocardiography, Wen has practiced medicine since 2007. Moreover, he has extensive training in different aspects of cardiovascular care including non-invasive and invasive cardiovascular evaluation, advanced cardiovascular imaging and peripheral arterial and venous diseases.

    Want to know more about the challenges Xianfeng Wen has faced? Get the full details with our Challenge Study report.

    Discussion by the Court

    a. Marine Liability Expert—Captain Hafen

    REC Marine wished to exclude Hafen’s expert report and untimely report
    supplement. Defendant’s principal argument is that the first two sections of Hafen’s report are inadmissible because she based those opinions on REC Marine’s alleged lack of compliance with the International Safety Management Code (“ISM Code”), a set of regulations that arguably does not apply as a matter of law to the vessel Conner worked on.

    Because the M/V GOL Warrior did not fall into the category of vessels that are required to be in compliance with the ISM Code, REC Marine argued that the ISM Code is wholly inapplicable to this matter and thus rendered Hafen’s opinions unreliable since they rested on irrelevant safety standards as applied to this vessel. Additionally, REC Marine wished to exclude the third section of Hafen’s report because it inappropriately provided legal opinions on the Receipt & Release Agreement, which REC Marine argued went outside of the bounds of appropriate testimony for a marine liability expert. It also sought exclusion of her supplemental report that was untimely submitted on March 31, 2026—just over two months after the deadline for Plaintiff to produce his expert reports.

    Analysis

    1. Opinions Based on the ISM Code Are Permissible.

    The Court found that her expert testimony, reliant upon a seemingly widely accepted set of safety standards, provided the kind of specialized analysis that will assist the trier of fact in understanding the evidence in this case. REC Marine may challenge Hafen’s reliance on the ISM Code in cross-examination. And of course, the Court retained the ability to limit or control the scope of her testimony at trial. Overall, the Court will not limit or exclude Hafen’s testimony insofar as she pointed to the ISM Code in support of her conclusions.

    2. Opinions About the Receipt & Release Are Inadmissible

    REC Marine presses that the third section of Hafen’s expert report, which addressed the Jones Act, should be excluded both because it impermissibly reaches conclusions of law and because it goes beyond the scope of her expertise as a marine liability expert. The Court agreed. Moreover, Plaintiff “did not contest REC Marine’s motion to the extent it sought to prevent Hafen from opining concerning whether Conner’s release was consistent with the Jones Act.”

    3. The Supplemental Report Is Excluded, Unless Used for Rebuttal

    REC Marine asked the Court to exclude Hafen’s supplemental report because it is not a true supplement and instead contained new opinions and analyzed new data; thus, it should be excluded because it was disclosed over two months after Plaintiff’s deadline to provide his reports.

    The Court reviewed the report and found that it went beyond the scope of Hafen’s initial report and is not a mere supplementation to her timely-disclosed expert report. Importantly, the data analyzed in the supplemental report is publicly available and thus was not “unavailable to” Plaintiff nor Hafen at the time of her initial report.

    However, the Court noted that Hafen’s supplemental report was issued on March 31, 2026—within the 30-day rebuttal report deadline provided for in Rule 26(a)(2)(D)(ii). That rule provided that an expert disclosure must be made “within 30 days after the other party’s disclosure” so long as “the evidence is intended solely to contradict or rebut evidence on the same subject matter identified by another party under Rule 26(a)(2)(B) or (C).” To the extent Hafen’s report operates as a rebuttal report to Defendant’s marine liability expert’s report concerning the interpretation of AIS data, the Court will exercise its discretion at trial to allow Hafen to testify as to her supplemental report in this limited way, i.e., as a rebuttal report, if Defendant’s expert’s testimony addresses these issues.

    B. Wen’s Testimony Will Be Limited

    Wen is properly designated as a non-retained expert and therefore falls within the parameters of Rule 26(a)(2)(C), absolving him of the written report requirement of Rule 26(a)(2)(B). The only question this Court considers is the appropriate scope of his testimony.

    1. Compliance With Rule 26(a)(2)(C)

    While the disclosed topics are the sorts of subject matters district courts tend to allow treating physicians to testify about, the disclosure is completely silent as to the facts relied upon by Wen in forming his opinions, except for reference to his records.

    The Court agreed that mere reference to the medical records, without more, is insufficient to satisfy Rule 26(a)(2)(C)’s disclosure requirement because “ the question is not the level of specificity required in the summary, because Plaintiff has failed to produce any summary of the facts and opinions to which Wen is expected to testify.”

    Testimony from a treating physician is certainly important evidence. However, considering that Plaintiff has a retained medical expert who has seemingly issued a timely report that touches on causation and future treatment, it is less important for Plaintiff’s treating physician to testify about causation and future treatment. Prejudice to REC Marine is most likely minimal, and REC Marine raised no prejudice arguments in its briefing. Furthermore, Defendant had the opportunity to take Wen’s deposition and, if it did, glean his perspective on causation and future medicals from his vantage point as a treating physician.

    Overall, the Court will not exclude the defect in Plaintiff’s Rule 26 disclosures
    for Wen because such defect is most likely harmless to REC Marine.

    2. Duplicative Expert Testimony Under Rule 403

    Defendant cited no case wherein a district court has excluded a second medical causation or future medical treatment opinion as cumulative pursuant to Rule 403. As such, the Court will not, at this time, restrict Plaintiff from calling both a retained expert who specifically produced a report on causation and a non-retained expert who may be able to testify as to causation if his opinions are based on his personal treatment of Conner and nothing more.

    Held

    The Court granted in part and denied in part the motions to exclude and/or limit the testimony of Captain Christine Hafen and Dr. Xianfeng Wen.

    Basically, the motions were granted to the extent that Hafen (1) may only testify as to her supplemental report if it can be properly considered a rebuttal report under Rule 26(e), and (2) may not testify as to the Receipt & Release Agreement. The motions were denied with prejudice as to Hafen’s opinions based upon the ISM Code.

    Also, the motions were denied without prejudice as to Xianfeng Wen’s testimony as a non-retained expert.

    Key Takeaway

    Rule 26(e) allowed the supplementation of a disclosure, such as an expert report, “in a timely manner if the party learns that in some material respect the disclosure or response is incomplete or incorrect.” But supplementation is not limitless; courts have found that “expert reports may only be supplemented in limited circumstances, specifically where supplementation ‘means correcting inaccuracies, or filling the interstices of an incomplete report based on information that was not available at the time of the initial disclosure.’”

    Case Details:

    Case Caption: Conner V. Rec. Marine Logistics, Llc
    Docket Number: 2:25cv458
    Court Name: United States District Court, Louisiana Eastern
    Order Date: April 21, 2026
  • Ophthalmology Expert’s Future Treatment Opinion Admitted

    Ophthalmology Expert’s Future Treatment Opinion Admitted

    This case arises from a trip and fall Plaintiff, Vivian Conerly, experienced on June 27, 2022 in the Hobby Lobby store in Hattiesburg, Mississippi. As she entered the store’s vestibule and rounded a display table, her shin struck a metal cart, and she fell face first onto the store’s concrete floor.

    Plaintiffs designated Dr. Jaime Jiménez as an expert. Jiménez is expected to testify that Conerly’s fall at Hobby Lobby caused the tributary branch retinal vein occlusion (“BRVO”) in her left eye and that she will require retinal injections as future treatment for this condition.

    However, Hobby Lobby sought to exclude his causation opinion on the grounds that it is unreliable because his opinion is based on facts he did not ask, examine, or otherwise determine from his treatment of Conerly.

    Ophthalmology Expert Witness

    Dr. Jaime Jiménez-Agosto is a board-certified ophthalmic surgeon. He is also fellowship-trained in vitreoretinal surgery. He has performed over fifteen thousand vitrectomies and more than fifty thousand retinal procedures.

    Get the full story on challenges to Jaime Jiménez’s expert opinions and testimony with an in-depth Challenge Study.

    Discussion by the Court

    A. Causation Opinion

    Hobby Lobby asserted that Jiménez’s opinion is unreliable because Jiménez admitted that he does not know whether Conerly performed a Valsalva maneuver and instead relies on the assumption that she did because he personally holds his breath when he falls.

    Having reviewed the record evidence, the Court found that Jiménez’s opinion that the fall caused Conerly’s tributary BRVO is not based on assumptions or ipse dixit. Instead, Jiménez reviewed Conerly’s history; he reviewed her deposition and noted that after the fall she immediately complained of pain in her eye and exhibited symptoms consistent with a tributary BRVO; he personally examined her and ran tests that showed the retinal swelling had gotten worse; and, most importantly, he watched the video that showed her falling rapidly and hitting the ground with the left side of her face, which arguably could be better evidence than Conerly’s own recollection. These are the types of records, documents and materials commonly relied on by medical experts.

    Hobby Lobby is asking the Court to assign significance to Jiménez’s “lack of factual knowledge” based on unestablished supposition of what is required for a tributary BRVO to occur. The record is not clear—could hitting one’s eye with significant force be enough? Would only compressing the abdominal area be enough? Without knowing exactly what is required, it is further unclear whether Conerly performing a “Valsalva maneuver” is even necessary. Similarly, as for Jiménez’s not knowing what delta-v force occurred presupposes that there must be a specific delta-v force experienced before a tributary BRVO can occur. Given the state of the record, the Court found that these are issues to be addressed on cross-examination.

    B. Future Treatment Opinion

    Moreover, Hobby Lobby sought to exclude any opinion regarding future treatment on the grounds that it is too speculative.

    Jiménez is one of Conerly’s treating physicians. He has testified about the healing process of a tributary BRVO—that it must be monitored and that treatment for swelling is provided when needed. With BRVO treatment, “you stretch it out as much as you can, but it’s very frequent to have relapses.”

    He treated Conerly on a regular basis throughout 2025. Basically, his ongoing evaluations provided him with additional clinical observations and data to refine his opinions.

    Therefore, the Court found that Jiménez’s opinion as a treating physician regarding future medical treatment was admissible.

    Held

    The Court denied Defendant’s motion to exclude or limit the testimony of Dr. Jaime Jiménez.

    Key Takeaway

    An expert may base an opinion on facts or data in the case that the expert has been made aware of or personally observed. As a general rule, questions relating to the bases and sources of an expert’s opinion affect the weight to be assigned to that opinion rather than its admissibility and should be left for the jury’s consideration.

    Case Details:

    Case Caption: Conerly V. Hobby Lobby Stores, Inc.
    Docket Number: 2:24cv118
    Court Name: United States District Court, Mississippi Southern
    Order Date: March 20, 2026
  • Polymers Expert Allowed to Opine on PFOS Sources

    Polymers Expert Allowed to Opine on PFOS Sources

    This case arises out of the contamination of surface waters and drinking water in Chattooga County, Georgia, with per- and polyfluoroalkyl substances known as “PFAS.”

    In essence, Plaintiff Earl Parris, Jr., alleged that the Defendants have contaminated his water with PFAS. Parris is a resident of Summerville, Georgia, who receives running, potable water to his home from the Summerville Public Works and Utilities Department.

    The City of Summerville—which has intervened in this case—used Raccoon Creek, a tributary of the Chattooga River, as the main source of its municipal water supply. Parris alleged that Raccoon Creek and—consequently, his household water—have been contaminated with PFAS by the Defendants. At present, Parris and Summerville jointly moved to exclude the opinion testimony of Defendant 3M’s expert, Maureen Reitman.

    Polymers Expert Witness

    Maureen Theresa Fahey Reitman, Sc.D. has been practicing in the field of polymer science and engineering for more than 30 years.

    She has a Doctor of Science in Materials Science and Engineering, with a thesis in the field of polymers, from MIT. She is also a licensed Professional Engineer in the state of Maryland and a Fellow of the Society of Plastics Engineers.

    Get the full story on challenges to Maureen Reitman’s expert opinions and testimony with an in-depth Challenge Study.

    Discussion by the Court

    Relevancy and Likelihood of Confusion

    Plaintiffs asserted that Reitman failed to identify any perfluorooctane sulfonate (PFOS)-containing products at the Mount Vernon Mill or the Trion Water Pollution Control Plant (“Trion Plant”) other than 3M’s product.

    The Court agreed with 3M that Reitman’s opinions as to other possible sources of PFAS and PFOS in the Raccoon Creek watershed are relevant to the issue of causation. Although it is 3M’s burden to establish the relevance and reliability of their expert’s opinions, it is ultimately the Plaintiffs’ burden at trial to prove the causal connection between their alleged injuries and the Defendants’ alleged actions.

    Here, 3M sought to introduce evidence undermining the Plaintiffs’ causation evidence by showing that there were other possible causes of the Plaintiffs’ injuries. Thus, the Plaintiffs’ argument that Reitman cannot determine “to what extent, if any, a participant in the global supply and use network for PFAS released a particular substance into the environment at issue” entirely missed the mark—the fact that Reitman is testifying she cannot make this determination is the whole point of introducing her testimony.

    3M intended to rely on this testimony to argue that the Plaintiffs cannot prove its product is the cause of the alleged PFAS contamination in the Raccoon Creek watershed.

    The Plaintiffs also sought to exclude Reitman’s opinions under Federal Rule of Evidence 403, arguing that her testimony about PFOS sources manufactured abroad will confuse the jury because such sources are irrelevant to their claims. Because Reitman’s testimony is relevant and will be helpful for the jury, the extraordinary remedy of exclusion under Rule 403 is unwarranted here.

    Reliability

    Plaintiffs asserted that Reitman admitted she does not have any data indicating PFOS sources besides 3M’s product are present in the Raccoon Creek watershed, yet she seeks to testify that other possible sources exist.

    However, Reitman’s report explains the reasons why the identification of PFOS and PFAS “in an environmental sample is not sufficient to identify the original source of production.” Further, she explains why this is true regardless of the characteristics in a sample associated with electrochemical fluorination (ECF), a process that 3M is known to have utilized in processing PFOS.

    And she provided testimony critical to 3M’s causation defense that the Plaintiffs have not provided an appropriate scientific basis for excluding other possible suppliers of the specific PFAS at issue due to the potential contributions of products associated with global supply chains.

    The fact that Reitman’s opinions may undermine the causation evidence the Plaintiffs intend to present does not make them unreliable; instead, the Plaintiffs’ concern goes to the weight and credibility of the evidence. The Plaintiffs will have the opportunity to cross-examine Reitman at trial, where their concerns will be more appropriately addressed.

    Held

    The Court denied the Plaintiff and Intervenor-Plaintiff’s joint motion to exclude the opinions of Maureen Reitman.

    Key Takeaway

    In the Court’s view, the Plaintiffs did not truly challenge the reliability of Reitman’s opinions, but instead challenged the content of her opinions. But the Court’s inquiry at this stage “must be solely on principles and methodology, not on the conclusions that they generate.”

    Case Details:

    Case Caption: Parris V. 3M Company
    Docket Number: 4:21cv40
    Court Name: United States District Court, Georgia Northern
    Order Date: March 09, 2026
  • Valuation Expert Allowed to Opine on Stock Drop

    Valuation Expert Allowed to Opine on Stock Drop

    In this defamation action, Plaintiffs Techtronic Industries Company Limited and Techtronic Industries Factory Outlets, Inc. (“Plaintiffs” or “TTI”) sued Defendant Victor Bonilla (“Defendant” or “Bonilla”) for statements made about TTI and its business practices by Bonilla in two reports he authored and published on his website Jehoshaphat Research in February and June 2023.

    Bonilla filed a motion to exclude TTI’s expert Jeffrey W. Kopa, CFA under Fed. R. Evid. 702, arguing that Kopa’s qualifications and opinions failed to meet the standards required by Daubert and the Federal Rules of Evidence.

    Valuation Expert Witness

    Jeffrey William Kopa, CFA is a partner and managing director at AlixPartners in the Investigations, Disputes and Risk practice. He holds a Bachelor of Business Administration degree with an emphasis on finance and accounting from the University of Michigan and a Master of Business Administration degree and Master of Science degree in Finance from Indiana University School of Business. Kopa has developed an extensive litigation-consulting, financial, valuation, and investing practice over his past 20 years of professional experience.

    He has analyzed damages through his litigation-consultant services in a variety of areas including antitrust, audit malpractice, breach of contract, false advertising, intellectual property litigation, purchase price and transaction disputes, shareholder disputes, fraudulent conveyance, and preference actions. Kopa has experience examining damages and lost profits caused by alleged wrongful acts and has been qualified as an expert to present damages opinions and statistical analyses in state, federal, and bankruptcy courts. In addition to performing damages analyses, he has performed accounting investigations, assessed credit worthiness, advised creditors and board members, participated in capital raising efforts and worked to restructure and refinance companies.

    Get the full story on challenges to Jeffrey Kopa’s expert opinions and testimony with an in-depth Challenge Study.

    Discussion by the Court

    In his initial report, Kopa offered the following opinions:

    • The market for the common stock of TTI was open, developed, and efficient before and around the time of the Jehoshaphat Reports (“JR”) were publicly issued based on the results of standard market efficiency tests.
    • The share price of TTI’s common stock declined in February 23, 2023 and June 6, 2023, following the First Report and Second Report, respectively, and the negative abnormal return following the First Report’s publication was highly statistically significant.
    • Defendant profited from trading activity associated with the JR Reports.
    • TTI incurred approximately US$152 thousand in incremental professional fees to address the JR Reports.
    • TTI’s incremental compensation plans have a total attributable value to the JR Reports of approximately US$23.6 million.

    Defendant challenged Kopa’s second, fourth, and fifth opinions referenced above. Defendant noted that, with respect to the third opinion, Bonilla’s profits are not an item of damages that Plaintiffs may claim, but he did not otherwise challenge Kopa’s analysis or conclusion that Bonilla profited from trading activity associated with the reports.

    Qualifications

    Bonilla contended that Kopa offered no testimony on the salient issues that would be helpful to the jury, such as identifying which damages resulted from the alleged false and defamatory statements and whether the LTIP executive compensation program was necessary. This argument appeared to go to the last prong of the Daubert analysis and not to Kopa’s qualifications to offer a damages opinion in this case. As courts in this Circuit have noted, “the qualification standard for expert testimony is ‘not stringent’ and ‘so long as the expert is minimally qualified, objections to the level of the expert’s expertise go to credibility and weight, not admissibility.’”

    Given Kopa’s education, experience, and credentials, the Court found that Kopa is at least minimally qualified to offer damages opinions in this case.

    Methodology

    In formulating his opinions, Kopa utilized the methodology of an “event study” to analyze the impact of Bonilla’s reports on TTI’s stock. An event study is a statistical regression analysis that examines the effect of an event—such as the release of information—on a dependent variable, such as a corporation’s stock price. Kopa testified that he combined a quantitative analysis of the change in TTI’s stock with a qualitative loss causation analysis of TTI-focused news. 

    Bonilla argued that although Kopa purports to conduct an event study to show the connection between the First and Second Reports and the stock drop, he did not use any methodology to determine if the stock drops were due to the alleged false and defamatory statements, as opposed to being due to true statements or opinions in the reports.

    As event studies are a “common method” of establishing loss causation, the Court found Kopa’s methodology to be generally accepted in the scientific community and therefore reliable.

    Kopa also used the net present value technique, a commonly accepted methodology, to calculate TTI’s damages. Bonilla argued that Kopa’s analysis of the legal and accounting bills did not use an accepted methodology at all; rather, he just added them up. Bonilla complained that Kopa did not analyze whether the legal and accounting work performed was necessary.

    For the same reason, he challenged Kopa’s testimony about the executive compensation issue contending Kopa merely asserts a but-for test that is unscientific and unreliable. Whether or not the services were needed does not appear to be an opinion that Kopa is offering.

    Net present value analyses are an acceptable and common methodology used by financial experts. Basically, the Court found that Kopa’s causation assumption did not render his damages opinion inadmissible.

    Helpfulness to the Jury

    TTI contended that Kopa did not simply look at a stock market drop as Bonilla suggests. TTI represented that Kopa’s opinions are formed based upon a statistical causal analysis utilizing an event study. Bonilla’s arguments to the contrary in an effort to exclude the opinions go more to the weight the jury should give the opinions and not to their admissibility. Finally, Bonilla complained that some of the calculations are simple math calculations for which an expert is not needed. However, this is not a basis to exclude the expert.

    Held

    The Court denied Defendant Bonilla’s Daubert motion with respect to Jeffrey W. Kopa’s damages opinions.

    Key Takeaway

    Relevant expert testimony logically advances a material aspect of the proposing party’s case and fits the disputed facts.

    While performing simple mathematical calculations or conversion of money from Hong Kong to U.S. dollars may not necessarily require expert testimony, to the extent that Kopa is permitted to testify, his performance of these calculations and conversions will be helpful to the jury.

    Case Details:

    Case Caption: Techtronic Industries Company Limited V. Bonilla
    Docket Number: 8:23cv1734
    Court Name: United States District Court, Florida Middle
    Order Date: March 06, 2026