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Expert testimony in New York is evaluated differently depending on whether the case proceeds in state or federal court: state courts generally apply Frye to contested novel scientific methods, while federal courts apply Rule 702 and Daubert. This article compares the two frameworks, explains CPLR 3101(d) disclosure requirements, and identifies common risks involving unsupported assumptions, analytical gaps, unreliable application, and inadequate disclosures.
In New York litigation, expert testimony can change the direction of a case well before trial. It can influence settlement value, shape summary judgment strategy, and determine whether a jury hears a clear, credible story or ends up sorting through competing technical claims.
Because New York state and federal courts apply different admissibility frameworks, New York attorneys often have to think about expert issues through two lenses. In New York state courts, Frye often comes into play when expert testimony depends on a novel scientific principle, procedure, or technique and general acceptance in the relevant scientific community is genuinely disputed. In federal courts in New York, Federal Rule of Evidence 702 and the Daubert line of cases govern, requiring the court to screen for reliability, helpfulness, and reliable application to the case facts.
That difference is not academic. It affects what you need to prove, how you build the record, and what the other side will attack first. In state court, disputes often turn on whether a challenged approach is genuinely novel and whether the relevant community generally accepts it. In federal court, disputes more often focus on whether the opinion is supported by sufficient facts or data, uses reliable methods, and applies those methods reliably to the record. The 2023 amendment to Rule 702 reinforces that the proponent must satisfy the more-likely-than-not standard that the Rule 702 requirements are met.
Just as important, New York courts emphasize a practical point that can get overlooked: Frye is not the entire admissibility inquiry. Even if a method is generally accepted, New York courts still require a proper foundation showing that accepted methods were appropriately applied to the facts of the case.
This guide explains how Frye and the federal Rule 702 and Daubert framework differ in real New York practice, and how to build an admissibility record that holds up in either venue.
In practice, admissibility can shape strategy earlier than most teams expect. It can affect expert selection, discovery sequencing, expert disclosure, and how you prepare for motion practice.
Key reasons this matters include:
In New York litigation, expert testimony can change the direction of a case well before trial. It can influence settlement value, shape summary judgment strategy, and determine whether a jury hears a clear, credible story or ends up sorting through competing technical claims.
Because New York state and federal courts apply different admissibility frameworks, New York attorneys often have to think about expert issues through two lenses. In New York state courts, Frye often comes into play when expert testimony depends on a novel scientific principle, procedure, or technique and general acceptance in the relevant scientific community is genuinely disputed. In federal courts in New York, Federal Rule of Evidence 702 and the Daubert line of cases govern, requiring the court to screen for reliability, helpfulness, and reliable application to the case facts.
That difference is not academic. It affects what you need to prove, how you build the record, and what the other side will attack first. In state court, disputes often turn on whether a challenged approach is genuinely novel and whether the relevant community generally accepts it. In federal court, disputes more often focus on whether the opinion is supported by sufficient facts or data, uses reliable methods, and applies those methods reliably to the record. The 2023 amendment to Rule 702 reinforces that the proponent must satisfy the more-likely-than-not standard that the Rule 702 requirements are met.
Just as important, New York courts emphasize a practical point that can get overlooked: Frye is not the entire admissibility inquiry. Even if a method is generally accepted, New York courts still require a proper foundation showing that accepted methods were appropriately applied to the facts of the case.
This guide explains how Frye and the federal Rule 702 and Daubert framework differ in real New York practice, and how to build an admissibility record that holds up in either venue.
In practice, admissibility can shape strategy earlier than most teams expect. It can affect expert selection, discovery sequencing, expert disclosure, and how you prepare for motion practice.
Key reasons this matters include:
If you want a practical shortcut, start here. These differences often drive early decisions about vetting, scope, disclosure, and how to build your motion record.
Under Frye v. United States, the key question is whether a novel scientific principle, procedure, or technique has general acceptance in the relevant scientific community. New York courts have continued to use Frye in state court, including in cases such as People v. Wesley and Cornell v. 360 W. 51st St. Realty, LLC.
As a practical matter, Frye disputes often come down to three pressure points:
A strong Frye record usually does not rely on labels alone. It shows what practitioners do in real work, what literature or standards support the method, what guardrails exist, and why the expert’s approach fits within those guardrails.
In federal court, the focus often shifts. Daubert v. Merrell Dow Pharmaceuticals, Inc., General Electric Co. v. Joiner, and Kumho Tire Co. v. Carmichael form the core federal framework for expert admissibility. Courts may consider whether a method is generally accepted in the field, but admissibility still turns on Rule 702’s reliability and fit requirements.
As a practical matter, Rule 702 challenges often focus on concrete issues such as:
On the defense side, the most persuasive response is usually a methods narrative the court can follow without guessing. It lays out the inputs, the steps, the decision points, the limits, and the connection between the method and the case facts.
Frye and Daubert are different frameworks, but the contrast should not be overstated. General acceptance can still matter in federal court because Daubert treats it as one possible reliability factor. At the same time, New York Frye practice is not limited to a narrow acceptance question because courts still require a proper foundation and a reliable connection between the method and the facts.
That distinction can matter in close cases. Frye may be more difficult for emerging methods that are scientifically sound but not yet generally accepted by a clear majority or substantial portion of the relevant community. Daubert may allow a court to consider the underlying reliability of that method more directly. In other cases, a method may be generally accepted but still fail because the expert’s case-specific application is weak.
Even when the general science is accepted, courts still expect a defensible connection between inputs and conclusions. If the reasoning skips steps or the application is not grounded in the record, the opinion becomes vulnerable, whether the challenge is framed as a Frye issue, a foundation problem, a disclosure problem, or a Rule 702 motion.
In practice, exclusions often come from gaps that are hard to defend once the record is locked. What tends to matter most is whether the expert can explain the path from inputs to conclusions in a way that stays consistent with the record, the method, the disclosure, and the limits of the discipline.
Common vulnerability points that often show up in motions and hearings include:
If you are trying to build a record that holds up in either forum, these are the failure points worth pressure-testing early.
New York generally applies Frye when a party offers expert testimony that depends on a novel scientific principle, procedure, or technique and general acceptance is genuinely in dispute. The core question is whether the methodology is generally accepted in the relevant scientific community.
In practice, courts often separate two issues:
That separation matters. Frye can be satisfied, and the opinion can still fail because the expert did not build a defensible bridge from the record to the conclusion.
In New York state court, the proponent of the challenged expert testimony generally bears the burden of showing that the scientific principle, procedure, or technique is generally accepted in the relevant scientific community.
That burden matters in real motion practice. The proponent cannot simply say the expert is qualified or that the method sounds reliable. The proponent should be ready to show acceptance through sources such as peer-reviewed literature, professional standards, prior judicial decisions, practical use in the field, and testimony from qualified experts.
General acceptance does not require unanimous agreement. Scientific communities often disagree. But the proponent should be prepared to show that the method has meaningful acceptance within the relevant field, not just support from a small group of litigation experts.
For the opponent, the burden issue shapes strategy too. The opponent does not always need to disprove the science outright. Sometimes the stronger argument is that the proponent has not carried the burden of proving general acceptance in the first place.
Even after a court is satisfied that a method is generally accepted, the opinion can still fail if the expert cannot show how accepted principles were applied to the facts in a careful, record-supported way.
In federal court, judges act as gatekeepers under Rule 702 and Daubert to ensure expert testimony is both reliable and helpful to the factfinder. Courts may consider testing, peer review, error rates, standards, and general acceptance, but the inquiry is flexible and depends on the field and the opinion.
The federal framework does not ask only whether an expert is credentialed. It asks whether the opinion rests on sufficient facts or data, whether reliable principles and methods were used, and whether those principles and methods were reliably applied to the facts of the case.
Kumho Tire settled that the federal gatekeeping obligation applies to scientific, technical, and other specialized knowledge. That includes engineers, accountants, physicians, damages experts, software experts, industry experts, and other non-laboratory professionals when they offer expert opinion testimony.
For modern motion practice, the point is not simply that Kumho Tire applies beyond laboratory science. That is settled law. The more important question is how the expert explains the reliability of the method used in the specific discipline and how closely that method fits the case facts.
Effective December 1, 2023, Rule 702 was amended to emphasize that expert testimony may be admitted only if the proponent demonstrates, under the more-likely-than-not standard, that the Rule 702 requirements are satisfied. The amendment also emphasizes that the court must decide sufficiency of the expert’s basis and the reliability of the expert’s application as part of admissibility under Rule 702, not simply leave those issues to the jury.
This is important for attorneys because arguments once framed as “weight, not admissibility” may now receive closer gatekeeping attention. The court must decide whether the expert’s basis, method, and application satisfy Rule 702 before the testimony reaches the jury.
A common federal argument focuses on the gap between what the data show and what the expert concludes. Joiner is especially important for this point because it recognizes that courts do not have to admit opinion testimony when there is too great an analytical gap between the data and the opinion offered.
If the expert starts with acceptable materials but makes a leap the record cannot support, the opinion becomes vulnerable. Strong motions identify the leap and force the proponent to explain the missing steps.
New York state court expert practice does not work the same way as federal expert discovery. In federal court, Rule 26 often requires formal expert reports for retained experts. In New York state court, CPLR 3101(d)(1) governs expert disclosure.
That distinction matters because New York state court disclosure often becomes the practical roadmap for the expert’s testimony. The disclosure generally identifies the expert’s qualifications, the subject matter of the testimony, the substance of the facts and opinions on which the expert is expected to testify, and a summary of the grounds for each opinion.
A vague disclosure can create problems even if the expert’s underlying method is defensible. If the disclosure does not fairly explain the substance of the opinions or the grounds for them, the opponent may argue prejudice, seek preclusion, or use the disclosure gap to narrow the expert’s trial testimony.
For Frye strategy, CPLR 3101(d) matters because the disclosure can frame what methodology is being offered, what opinions are being challenged, and whether the opposing party had fair notice of the expert’s scientific basis. A strong admissibility record should not live only in counsel’s file. It should be reflected in the materials the court and the opposing party will actually see.
In practice, the strongest admissibility records are built early, before the case is locked into a single expert narrative.
Identify the actual method, not just a label. Define the steps, standards, and decision points. If Frye is plausible, identify the relevant scientific community and the basis for treating it as the right community for general acceptance.
If state court is likely, collect the strongest general-acceptance support for any method the opponent may call novel. If federal court is possible, build the Rule 702 record at the same time, including data sources, standards followed, error-related considerations where relevant, and how the method is normally used in the field.
Many exclusions happen because the expert cannot clearly explain how the method was applied to the case facts. Your expert should be able to walk through the inputs relied on, the steps taken, and why the conclusion follows from those inputs. Where the discipline calls for it, the expert should also be prepared to explain how alternative explanations were addressed.
Keep conclusions within what the data and method can actually support. Make assumptions explicit, explain why they are reasonable, and be clear about limits.
In New York state court, do not treat CPLR 3101(d) disclosure as a formality. The disclosure should accurately reflect the expert’s qualifications, subject matter, opinions, factual basis, and grounds for those opinions. If a Frye challenge is foreseeable, the disclosure and supporting record should make the methodology clear enough for the court and the opponent to understand what is being offered.
A good admissibility record does more than cite Frye or Daubert in broad terms. It connects the issue to the cases that actually matter. Wesley may matter for DNA and New York Frye principles. Parker and Cornell may matter in toxic tort and causation disputes. LeGrand may matter in eyewitness identification cases. Daubert, Joiner, Kumho Tire, and Rule 702 matter in federal court. Using the right authorities helps keep the argument focused and credible.
Does New York Use Daubert?
In New York state court, Frye generally governs certain expert testimony tied to novel scientific principles or techniques when general acceptance is genuinely contested. In federal court in New York, Rule 702 and Daubert apply.
What Does Frye Test in New York?
Frye focuses on whether the relevant scientific community generally accepts the underlying scientific principle, procedure, or technique when that issue is genuinely in dispute.
Who Has the Burden at a Frye Hearing?
The proponent of the challenged expert testimony generally bears the burden of showing that the methodology is generally accepted in the relevant scientific community.
What Does Daubert Test?
Daubert and Rule 702 focus on reliability and helpfulness, including whether the expert used reliable methods and applied them reliably to the case facts.
What Changed With Rule 702 in 2023?
The amendment emphasizes that the proponent must show, under the more-likely-than-not standard, that Rule 702’s admissibility requirements are met, including sufficiency of facts or data and reliable application.
Can an Expert Be Admitted Under Frye But Excluded Under Rule 702?
Yes. A method can be generally accepted for Frye purposes, but still fail in federal court if the proponent cannot show sufficient facts or data, reliable methods, and reliable application to the record.
Why Does CPLR 3101(d) Matter in New York Expert Practice?
If you want a practical shortcut, start here. These differences often drive early decisions about vetting, scope, disclosure, and how to build your motion record.
Under Frye v. United States, the key question is whether a novel scientific principle, procedure, or technique has general acceptance in the relevant scientific community. New York courts have continued to use Frye in state court, including in cases such as People v. Wesley and Cornell v. 360 W. 51st St. Realty, LLC.
As a practical matter, Frye disputes often come down to three pressure points:
A strong Frye record usually does not rely on labels alone. It shows what practitioners do in real work, what literature or standards support the method, what guardrails exist, and why the expert’s approach fits within those guardrails.
In federal court, the focus often shifts. Daubert v. Merrell Dow Pharmaceuticals, Inc., General Electric Co. v. Joiner, and Kumho Tire Co. v. Carmichael form the core federal framework for expert admissibility. Courts may consider whether a method is generally accepted in the field, but admissibility still turns on Rule 702’s reliability and fit requirements.
As a practical matter, Rule 702 challenges often focus on concrete issues such as:
On the defense side, the most persuasive response is usually a methods narrative the court can follow without guessing. It lays out the inputs, the steps, the decision points, the limits, and the connection between the method and the case facts.
Frye and Daubert are different frameworks, but the contrast should not be overstated. General acceptance can still matter in federal court because Daubert treats it as one possible reliability factor. At the same time, New York Frye practice is not limited to a narrow acceptance question because courts still require a proper foundation and a reliable connection between the method and the facts.
That distinction can matter in close cases. Frye may be more difficult for emerging methods that are scientifically sound but not yet generally accepted by a clear majority or substantial portion of the relevant community. Daubert may allow a court to consider the underlying reliability of that method more directly. In other cases, a method may be generally accepted but still fail because the expert’s case-specific application is weak.
Even when the general science is accepted, courts still expect a defensible connection between inputs and conclusions. If the reasoning skips steps or the application is not grounded in the record, the opinion becomes vulnerable, whether the challenge is framed as a Frye issue, a foundation problem, a disclosure problem, or a Rule 702 motion.
In practice, exclusions often come from gaps that are hard to defend once the record is locked. What tends to matter most is whether the expert can explain the path from inputs to conclusions in a way that stays consistent with the record, the method, the disclosure, and the limits of the discipline.
Common vulnerability points that often show up in motions and hearings include:
If you are trying to build a record that holds up in either forum, these are the failure points worth pressure-testing early.
New York generally applies Frye when a party offers expert testimony that depends on a novel scientific principle, procedure, or technique and general acceptance is genuinely in dispute. The core question is whether the methodology is generally accepted in the relevant scientific community.
In practice, courts often separate two issues:
That separation matters. Frye can be satisfied, and the opinion can still fail because the expert did not build a defensible bridge from the record to the conclusion.
In New York state court, the proponent of the challenged expert testimony generally bears the burden of showing that the scientific principle, procedure, or technique is generally accepted in the relevant scientific community.
That burden matters in real motion practice. The proponent cannot simply say the expert is qualified or that the method sounds reliable. The proponent should be ready to show acceptance through sources such as peer-reviewed literature, professional standards, prior judicial decisions, practical use in the field, and testimony from qualified experts.
General acceptance does not require unanimous agreement. Scientific communities often disagree. But the proponent should be prepared to show that the method has meaningful acceptance within the relevant field, not just support from a small group of litigation experts.
For the opponent, the burden issue shapes strategy too. The opponent does not always need to disprove the science outright. Sometimes the stronger argument is that the proponent has not carried the burden of proving general acceptance in the first place.
Even after a court is satisfied that a method is generally accepted, the opinion can still fail if the expert cannot show how accepted principles were applied to the facts in a careful, record-supported way.
In federal court, judges act as gatekeepers under Rule 702 and Daubert to ensure expert testimony is both reliable and helpful to the factfinder. Courts may consider testing, peer review, error rates, standards, and general acceptance, but the inquiry is flexible and depends on the field and the opinion.
The federal framework does not ask only whether an expert is credentialed. It asks whether the opinion rests on sufficient facts or data, whether reliable principles and methods were used, and whether those principles and methods were reliably applied to the facts of the case.
Kumho Tire settled that the federal gatekeeping obligation applies to scientific, technical, and other specialized knowledge. That includes engineers, accountants, physicians, damages experts, software experts, industry experts, and other non-laboratory professionals when they offer expert opinion testimony.
For modern motion practice, the point is not simply that Kumho Tire applies beyond laboratory science. That is settled law. The more important question is how the expert explains the reliability of the method used in the specific discipline and how closely that method fits the case facts.
Effective December 1, 2023, Rule 702 was amended to emphasize that expert testimony may be admitted only if the proponent demonstrates, under the more-likely-than-not standard, that the Rule 702 requirements are satisfied. The amendment also emphasizes that the court must decide sufficiency of the expert’s basis and the reliability of the expert’s application as part of admissibility under Rule 702, not simply leave those issues to the jury.
This is important for attorneys because arguments once framed as “weight, not admissibility” may now receive closer gatekeeping attention. The court must decide whether the expert’s basis, method, and application satisfy Rule 702 before the testimony reaches the jury.
A common federal argument focuses on the gap between what the data show and what the expert concludes. Joiner is especially important for this point because it recognizes that courts do not have to admit opinion testimony when there is too great an analytical gap between the data and the opinion offered.
If the expert starts with acceptable materials but makes a leap the record cannot support, the opinion becomes vulnerable. Strong motions identify the leap and force the proponent to explain the missing steps.
New York state court expert practice does not work the same way as federal expert discovery. In federal court, Rule 26 often requires formal expert reports for retained experts. In New York state court, CPLR 3101(d)(1) governs expert disclosure.
That distinction matters because New York state court disclosure often becomes the practical roadmap for the expert’s testimony. The disclosure generally identifies the expert’s qualifications, the subject matter of the testimony, the substance of the facts and opinions on which the expert is expected to testify, and a summary of the grounds for each opinion.
A vague disclosure can create problems even if the expert’s underlying method is defensible. If the disclosure does not fairly explain the substance of the opinions or the grounds for them, the opponent may argue prejudice, seek preclusion, or use the disclosure gap to narrow the expert’s trial testimony.
For Frye strategy, CPLR 3101(d) matters because the disclosure can frame what methodology is being offered, what opinions are being challenged, and whether the opposing party had fair notice of the expert’s scientific basis. A strong admissibility record should not live only in counsel’s file. It should be reflected in the materials the court and the opposing party will actually see.
In practice, the strongest admissibility records are built early, before the case is locked into a single expert narrative.
Identify the actual method, not just a label. Define the steps, standards, and decision points. If Frye is plausible, identify the relevant scientific community and the basis for treating it as the right community for general acceptance.
If state court is likely, collect the strongest general-acceptance support for any method the opponent may call novel. If federal court is possible, build the Rule 702 record at the same time, including data sources, standards followed, error-related considerations where relevant, and how the method is normally used in the field.
Many exclusions happen because the expert cannot clearly explain how the method was applied to the case facts. Your expert should be able to walk through the inputs relied on, the steps taken, and why the conclusion follows from those inputs. Where the discipline calls for it, the expert should also be prepared to explain how alternative explanations were addressed.
Keep conclusions within what the data and method can actually support. Make assumptions explicit, explain why they are reasonable, and be clear about limits.
In New York state court, do not treat CPLR 3101(d) disclosure as a formality. The disclosure should accurately reflect the expert’s qualifications, subject matter, opinions, factual basis, and grounds for those opinions. If a Frye challenge is foreseeable, the disclosure and supporting record should make the methodology clear enough for the court and the opponent to understand what is being offered.
A good admissibility record does more than cite Frye or Daubert in broad terms. It connects the issue to the cases that actually matter. Wesley may matter for DNA and New York Frye principles. Parker and Cornell may matter in toxic tort and causation disputes. LeGrand may matter in eyewitness identification cases. Daubert, Joiner, Kumho Tire, and Rule 702 matter in federal court. Using the right authorities helps keep the argument focused and credible.
Does New York Use Daubert?
In New York state court, Frye generally governs certain expert testimony tied to novel scientific principles or techniques when general acceptance is genuinely contested. In federal court in New York, Rule 702 and Daubert apply.
What Does Frye Test in New York?
Frye focuses on whether the relevant scientific community generally accepts the underlying scientific principle, procedure, or technique when that issue is genuinely in dispute.
Who Has the Burden at a Frye Hearing?
The proponent of the challenged expert testimony generally bears the burden of showing that the methodology is generally accepted in the relevant scientific community.
What Does Daubert Test?
Daubert and Rule 702 focus on reliability and helpfulness, including whether the expert used reliable methods and applied them reliably to the case facts.
What Changed With Rule 702 in 2023?
The amendment emphasizes that the proponent must show, under the more-likely-than-not standard, that Rule 702’s admissibility requirements are met, including sufficiency of facts or data and reliable application.
Can an Expert Be Admitted Under Frye But Excluded Under Rule 702?
Yes. A method can be generally accepted for Frye purposes, but still fail in federal court if the proponent cannot show sufficient facts or data, reliable methods, and reliable application to the record.
Why Does CPLR 3101(d) Matter in New York Expert Practice?
CPLR 3101(d) governs expert disclosure in New York state court. It can affect notice, motion practice, trial scope, and preclusion arguments. A strong expert record should be reflected in the disclosure, not just developed informally.
Legal Standards
Legal Standards
CPLR 3101(d) governs expert disclosure in New York state court. It can affect notice, motion practice, trial scope, and preclusion arguments. A strong expert record should be reflected in the disclosure, not just developed informally.