The Thin Line Between Expert and Lay Testimony

The Thin Line Between Expert and Lay Testimony

The Importance of Expert Testimony

Expert testimony is critical in cases with complex issues, including causation. Like all state and federal jurisdictions, Texas has robust jurisprudence that guides the admissibility of expert evidence and establishes when expert testimony is necessary.  If an issue is beyond an ordinary juror’s knowledge, then expert testimony is required.[i]   Generally, the more technical the issue, the more likely a party will need to use expert testimony.  However, the distinction between expert and lay testimony can become blurred, complicating a case and creating uncertainty.


Major Flooding Calls Engineering Designs and Construction into Question

Tenaris Bay City Inc. v. Ellisor concerns flooding damage to multiple homes during Hurricane Harvey[ii].  30 plaintiffs alleged the owner of a neighboring manufacturing facility negligently caused their properties to flood during Hurricane Harvey.  The plaintiffs attacked the construction of a drainage system, arguing that its failure to meet the design specifications caused the flooding.  In addition to naming the manufacturer, the plaintiffs named the engineering firm responsible for designing the system and the firm hired to verify that the plans were effective.  The parties presented conflicting lay and expert testimony, with the plaintiffs’ witnesses saying that the manufacturer caused the flooding and the manufacturer’s witnesses saying the property did not flood.  The jury found the manufacturer liable for negligence, negligent nuisance, and negligence per se in violation of the applicable water code.[iii]  The parties stipulated that the proper damages were $2.8 million.


Do Jurors Need Expert Testimony to Determine the Proximate Cause of Flooding?

On appeal, the manufacturer argued that the evidence was not legally sufficient to support the finding of proximate case.[iv]   Proximate cause requires evidence of 1) cause-in-fact and 2) foreseeability.[v]  Cause in fact is shown when the alleged act or omission was a substantial factor in causing the injuries and the injuries would not have occurred without it.[vi]  Foreseeability is shown that a person of ordinary intelligence should have anticipated the danger associated with their negligent act or omission.[vii]

In challenging the jury’s finding, the manufacturer took issue with the neighboring property owners’ civil engineering expert. The plaintiff and defense experts both testified that had the water drainage system been built as designed, the system would have been able to prevent flooding from a storm with Harvey’s severity; however, they disagreed as to whether the defendants built the system according to plan.  Based on an on-site visit and pictures taken, the neighboring property owners’ expert testified that the drainage system did not meet the design plan’s specifications.  He identified that a berm wall was lower in portions than in the plans and that the berm had various holes.  The expert opined that these deficiencies caused the water to escape, causing the flooding.  Non-experts also testified that in the twenty-seven years before the construction of the manufacturing facility, their properties had never flooded.  The manufacturer’s expert testified that the drainage system could not have failed because if it had, then the facility’s office would have flooded but they did not.  The manufacturer’s non-expert witness testified that he was onsite during the storm and that he did not see stormwater overflowing from the facility.

The attorney for the manufacturer focused the appeal on the exam of the plaintiffs’ expert. The expert testified that he did not analyze the plaintiffs’ homes and that he did not conduct a general flooding analysis. The expert also responded that he would not be able to answer the question as to what specifically caused the plaintiffs’ properties to flood. On re-direct, the expert testified that based on his education, work experience, and modelling, the design failure was a factor in flooding the plaintiffs’ properties.

The appellate court concluded that it did not matter that the expert gave conflicting opinions about causation because “it is the province of the jury to resolve conflicts in evidence, and when reasonable jurors could resolve conflicting evidence either way, we presume they did so in accordance with the verdict.”[viii]

At some point, the appellate court permitted the manufacturer to submit supplemental briefing.  In this briefing, the manufacturer argued that the case required expert testimony on causation because it concerned complex issues beyond a jury’s common understanding.  The appellate court disagreed.

Other appellate courts in Texas have concluded that flooding causation does not always require expert testimony.  The court explained that although a juror may not understand the natural flow of water or the engineering behind a storm-drainage system, they could understand that if a facility overflows it can cause flooding at nearby properties. Additionally, the court noted that the property owner never raised the issue before the trial court.


Could the Testimony Have Been Excluded on Other Grounds?

The court of appeals’ ruling exposes some potential issues with the admissibility of expert testimony.  Texas law has established various grounds for excluding expert testimony.  Of note, Texas law requires the exclusion of expert testimony when the jury is equally competent to opine about the ultimate fact issue or the evidence is within the jury’s common knowledge.[ix]  The logic for this rule is that if the jury has common knowledge, the testimony is of no assistance.[x]  State and federal courts have expressed concerns over the admissibility of expert testimony.[xi]  As the Texas Supreme Court has explained, “Expert witnesses can have an extremely prejudicial impact on the jury, in part because of the way in which the jury perceives a witness labeled as an expert.”[xii]  With this concern in mind, the Texas Supreme Court has established safeguards to the admissibility of expert testimony, like requiring experts to be qualified and to offer reliable opinions supported by proper methodology.[xiii]

The appellate court’s ruling has apparent inconsistencies. On one hand, the court concluded that the jury did not need expert testimony to understand that if one property floods, a neighboring property can flood. On the other hand, the court supported the verdict with expert testimony.  Although courts do not always have to exclude cumulative evidence[xiv], it is noteworthy that the court would support its decision to uphold the verdict with a mixture of lay and expert testimony when unchecked admissions of expert testimony is potentially prejudicial.  The plaintiffs and defendants had non-experts offer conflicting testimony of the flooding, so the jury would still have been faced with determining which testimony to believe and the verdict may have remained the same.



The inclusion or exclusion of expert testimony can be critical in cases.  As this case demonstrates, it is important to identify what evidence or testimony in a case can qualify as lay or expert testimony.  With the lines blurred between when a jury can decide an issue without expert testimony, it is critical to timely lodge all objections and submit for relief that will establish whether an issue like proximate cause requires expert testimony.  To support the position, it is important to work with experts to show why their particular expertise matters and why the particular issue goes beyond a juror’s common knowledge. Attacking an expert’s reliability and methodology through expert challenges is also key to excluding unfavorable testimony. Finally, one should not underestimate the importance of credible lay witnesses.  Good witnesses can be the last and most critical line of defense.




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[i] Unique Staff Leasing, Ltd. v. Cates, 500 S.W.3d 587, 592 (Tex. App.—Eastland 2016, pet. denied).

[ii] At the time of writing, the appellant’s petition for review to the Texas Supreme Court was still pending.

[iii] Tenaris Bay City Inc. v. Ellisor, No. 14-22-00013-CV, 2023 WL 5622855, at *1-2 (Tex. App.—Houston [14th Dist.] Aug. 31, 2023, pet. filed).

[iv] Id.

[v] Id.

[vi] Id.

[vii] Id.

[viii] Id. at  *4.

[ix] K-Mart Corp. v. Honeycutt, 24 S.W.3d 357, 360 (Tex. 2000).

[x] Id.

[xi] E.I. du Pont de Nemours & Co., Inc. v. Robinson, 923 S.W.2d 549, 553 (Tex. 1995)(“Professional expert witnesses are available to render an opinion on almost any theory, regardless of its merit.”).

[xii] Id.

[xiii] Id.

[xiv] Hooper v. Chittaluru, 222 S.W.3d 103, 107 (Tex. App.—Houston [14th Dist.] 2006, pet. denied).