New Wisconsin Law Clarifies Standards for Expert Witness Testimony

Analysis of 2025 Wisconsin Act 92 (Senate Bill 459)

Wisconsin lawmakers recently enacted 2025 Wisconsin Act 92, a law that modifies the evidentiary rule governing expert witness testimony in Wisconsin courts.

The legislation revises Wisconsin’s expert testimony statute so that it more closely mirrors Federal Rule of Evidence 702, which governs expert testimony in federal courts. The amendment clarifies the burden placed on the party offering expert testimony and the standard courts must apply when determining whether an expert’s opinion may be presented to a jury.

Because expert testimony is frequently used in criminal prosecutions – particularly in cases involving forensic evidence, scientific analysis, or technical investigations – the statute addresses how courts evaluate the reliability of expert opinions before they are admitted at trial.

Wisconsin’s Existing Expert Testimony Standard

Wisconsin courts already require expert testimony to meet reliability standards before it may be presented to a jury.

Under Wis. Stat. § 907.02, expert testimony is admissible if:

• the expert’s specialized knowledge will assist the trier of fact, and
• the testimony is based on reliable principles and methods applied to the facts of the case.

In 2011, Wisconsin adopted a version of the Daubert reliability framework, which requires courts to evaluate whether expert testimony is grounded in reliable scientific or technical methodology.

Under this framework, judges act as gatekeepers, determining whether expert testimony is sufficiently reliable to be presented to the jury.

What Act 92 Changes

Act 92 does not create a new evidentiary rule. Instead, it clarifies how courts should apply the existing reliability standard.

The amendment aligns Wisconsin’s statute more closely with the language of Federal Rule of Evidence 702, which was recently amended at the federal level.

The statute now explicitly states that the proponent of expert testimony must demonstrate that the testimony satisfies the rule’s reliability requirements.

Specifically, the court must determine that it is more likely than not that the expert testimony:

• is based on sufficient facts or data
• is the product of reliable principles and methods
• reflects a reliable application of those principles and methods to the facts of the case

This clarification emphasizes that courts must evaluate reliability before the testimony is presented to a jury.

The “More Likely Than Not” Standard

Act 92 clarifies that courts must evaluate expert testimony using a preponderance of the evidence standard.

Under this standard, the court must determine that it is more likely than not that the expert’s opinion satisfies the reliability requirements of the rule.

While Wisconsin courts already applied this standard in practice, the amendment makes the requirement explicit within the statute itself.

This reinforces the court’s role in determining whether expert testimony meets the necessary evidentiary threshold before it reaches the jury.

Practical Impact of the Change

Because Wisconsin had already adopted a Daubert-style reliability framework, the practical effect of Act 92 may be relatively modest.

The amendment primarily clarifies:

• that the party offering the expert bears the burden of demonstrating reliability
• that courts must apply the preponderance of the evidence standard when evaluating expert testimony
• that Wisconsin’s rule should be interpreted consistently with Federal Rule of Evidence 702

In practice, the statute may encourage courts to conduct more detailed evaluations of expert testimony before trial, particularly in cases involving complex scientific or technical evidence.

Why Expert Testimony Matters in Criminal Cases

Expert testimony frequently plays a central role in criminal prosecutions, particularly when juries must evaluate complex scientific or technical evidence.

Examples of expert testimony commonly used in criminal cases include:

• forensic DNA analysis
• toxicology reports
• digital forensic analysis
• accident reconstruction
• medical or psychological evaluations

Because juries often rely heavily on expert opinions when interpreting technical evidence, courts must ensure that such testimony is supported by reliable methods and sufficient data before it is presented at trial.

Act 92 reinforces the importance of that reliability review.

Key Takeaways from Wisconsin Act 92

2025 Wisconsin Act 92 clarifies how Wisconsin courts should evaluate expert witness testimony.

The most important points include:

• Wisconsin’s expert testimony rule now more closely aligns with Federal Rule of Evidence 702.
• The proponent of expert testimony bears the burden of demonstrating that the opinion meets the rule’s reliability requirements.
• Courts must determine that it is more likely than not that the testimony is based on sufficient facts, reliable methods, and proper application of those methods.
• The amendment largely clarifies existing evidentiary practice rather than creating a new standard.

What This Law Means Going Forward

Act 92 reinforces the role of courts in evaluating the reliability of expert testimony before it is presented to a jury.

Because expert opinions are frequently used in criminal prosecutions involving forensic science, digital evidence, and technical analysis, the clarified statutory language may influence how courts review expert testimony before trial.

Future court decisions will likely provide additional guidance on how Wisconsin judges apply the revised language when determining the admissibility of expert evidence.