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Federal Rules of Evidence
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Federal Rule of Evidence 703 governs the facts and data expert witnesses may rely on when forming opinions, including some information that may not itself be admissible at trial. This article explains the reasonable-reliance standard, how Rule 703 interacts with Rule 702, when underlying basis information may be disclosed to the jury, and the foundation problems attorneys should evaluate when vetting expert sources, assumptions, and methodology.
Federal Rule of Evidence 703 addresses a practical question in expert litigation: What facts or data may an expert rely on when forming an opinion?
Expert opinions may draw on records, reports, test results, photographs, testimony, and data or analysis produced by other professionals. Some of that material may not be independently admissible at trial. Rule 703 may still allow the expert to rely on it if experts in the particular field would reasonably rely on that kind of information when forming an opinion on the subject.
That does not mean the jury automatically gets to hear the material, and it does not make an unreliable opinion admissible.
This guide explains what Rule 703 allows, how it works with Rule 702, and which foundation problems can place expert testimony at risk.
Experts may base their opinions on facts or data they personally observed or were made aware of through other sources, including:
The expert does not always need to collect the information personally. Under Rule 703, the key question is whether experts in the particular field would reasonably rely on that kind of fact or data when forming an opinion on the subject.
Counsel and the court may consider where the information came from, its quality, and how the expert used it. Those factors may help show whether the reliance was reasonable and whether the opinion has a sufficient basis under Rule 702.
Depending on the issue, that material may include:
These sources are not automatically acceptable in every case. The proponent should be prepared to show, often through the expert’s explanation and evidence about professional practice in the field, why reliance on the material was reasonable and how the expert used it in forming the opinion.
As a practical matter, counsel may consider whether experts use the same kind of information in their professional work outside litigation. That may help show whether the reliance is consistent with professional practice in the field, although Rule 703 does not make use outside litigation an absolute requirement.
Counsel should ask:
Experts do not always need to perform every test themselves or personally collect every data point. The expert should still understand the information and its role in the analysis well enough to explain why reliance was reasonable in the field and how the information supports the opinion.
For example, suppose an engineer relies on measurements collected by a surveyor. In that situation, the opinion could face closer scrutiny if the engineer cannot explain what the survey measured, why reliance on it was reasonable, or whether the measurements relate to the correct location.
Federal Rule of Evidence 703 addresses a practical question in expert litigation: What facts or data may an expert rely on when forming an opinion?
Expert opinions may draw on records, reports, test results, photographs, testimony, and data or analysis produced by other professionals. Some of that material may not be independently admissible at trial. Rule 703 may still allow the expert to rely on it if experts in the particular field would reasonably rely on that kind of information when forming an opinion on the subject.
That does not mean the jury automatically gets to hear the material, and it does not make an unreliable opinion admissible.
This guide explains what Rule 703 allows, how it works with Rule 702, and which foundation problems can place expert testimony at risk.
Experts may base their opinions on facts or data they personally observed or were made aware of through other sources, including:
The expert does not always need to collect the information personally. Under Rule 703, the key question is whether experts in the particular field would reasonably rely on that kind of fact or data when forming an opinion on the subject.
Counsel and the court may consider where the information came from, its quality, and how the expert used it. Those factors may help show whether the reliance was reasonable and whether the opinion has a sufficient basis under Rule 702.
Depending on the issue, that material may include:
These sources are not automatically acceptable in every case. The proponent should be prepared to show, often through the expert’s explanation and evidence about professional practice in the field, why reliance on the material was reasonable and how the expert used it in forming the opinion.
As a practical matter, counsel may consider whether experts use the same kind of information in their professional work outside litigation. That may help show whether the reliance is consistent with professional practice in the field, although Rule 703 does not make use outside litigation an absolute requirement.
Counsel should ask:
Experts do not always need to perform every test themselves or personally collect every data point. The expert should still understand the information and its role in the analysis well enough to explain why reliance was reasonable in the field and how the information supports the opinion.
For example, suppose an engineer relies on measurements collected by a surveyor. In that situation, the opinion could face closer scrutiny if the engineer cannot explain what the survey measured, why reliance on it was reasonable, or whether the measurements relate to the correct location.
Rule 703 separates two questions:
An expert may be allowed to rely on inadmissible information even when the proponent is not permitted to disclose that information to the jury.
When the proponent seeks to disclose otherwise inadmissible basis information only to help the jury evaluate the expert’s opinion, the information’s value for that purpose must substantially outweigh its prejudicial effect. This demanding standard generally favors nondisclosure.
The Rule 703 balancing test does not control information that is independently admissible for another purpose under a different evidence rule.
Rule 703 is not a hearsay exception. An expert may sometimes rely on hearsay, but that does not automatically make the hearsay admissible or allow the expert to repeat it freely to the jury.
Rule 703 addresses whether an expert may rely on particular kinds of facts or data, including otherwise inadmissible information. Rule 702 governs whether the resulting testimony has a sufficient basis, uses reliable principles and methods, reflects a reliable application, and will help the trier of fact.
The witness must also be qualified by knowledge, skill, experience, training, or education. The proponent must then show that it is more likely than not that:
Reliance on a particular kind of information may meet Rule 703’s reasonable-reliance requirement while the resulting opinion still fails Rule 702.
For example, suppose an economist relies on government wage data. The opinion may still be unreliable if the expert selects an occupation, geographic market, or period that does not fit the claim and cannot explain the choice.
Rule 703 asks whether experts in the field would reasonably rely on that kind of information. Rule 702 asks whether the resulting testimony satisfies the full standard for admissibility.
Courts often say that disputes about an expert’s work go to weight rather than admissibility. The 2023 amendment clarified that questions about a sufficient basis and reliable application must first be decided by the court under Rule 702, rather than being treated automatically as matters of weight.
Under Rule 104(a), judges must decide whether the Rule 702 requirements are met. That includes whether the testimony is based on sufficient facts or data and whether the opinion reflects a reliable application of the expert’s principles and methods.
The proponent must show that those requirements have been met under the more likely than not standard.
For example, two experts may disagree about which of two reliably applied models better fits the evidence. Once the court determines that each opinion satisfies Rule 702, that remaining disagreement may affect the weight of the testimony.
By contrast, failing to consider critical data, explain a major assumption, or apply the stated method may create an admissibility problem.
It is not enough for an expert to identify a source that professionals in the field sometimes use. The expert should be able to explain why experts in the field would reasonably rely on the information and how it supports the particular opinion under Rule 702.
In practice, concerns about the expert’s factual basis or application may appear in several forms:
A method is not unreliable simply because it was developed for litigation. Still, the expert should be able to explain how the approach was tested, checked, applied consistently, or otherwise shown to be reliable for the opinion offered.
Under Daubert, trial judges examine reliability and fit. Joiner permits scrutiny of the gap between the data and the conclusion, and Kumho Tire confirms that the same gatekeeping duty applies to technical and other specialized testimony.
Reviewing the expert’s sources before the applicable disclosure or testimony deadline may reveal problems under Rules 702 and 703, as well as issues that could surface during deposition or cross-examination.
For each important source, counsel should ask:
Counsel should also identify every material assumption and ask where it came from. Even a long source list may leave an important question unanswered: Which materials actually shaped the expert’s analysis?
Finding those weaknesses early gives counsel a chance to investigate, clarify, narrow, or otherwise address them before deposition, cross-examination, or a Rule 702 motion.
Suppose a medical causation expert reviews hospital records, imaging studies, laboratory findings, an autopsy report, and treating-physician notes.
If specialists in the field would reasonably rely on those kinds of materials when evaluating causation, Rule 703 may allow the expert to base an opinion on them even when some underlying statements or information would otherwise be inadmissible.
The proponent must still show that the opinion is based on sufficient facts or data and that the expert reliably applied the methodology to the case. When alternative causes matter to the expert’s method or conclusion, counsel should also ask how the expert considered them.
The opinion may be vulnerable if it depends heavily on a patient history that lacks adequate support, uncertain timing that materially affects causation, or another physician’s unsupported impression.
The expert may be allowed to rely on the records without being allowed to repeat everything in them to the jury.
Suppose a damages expert relies on sales records, management projections, industry reports, and government economic data to calculate lost profits.
Rule 703 may permit reliance on these types of sources if experts in the relevant field would reasonably rely on them for that analysis.
Depending on the method and facts of the case, reliability concerns may arise if the expert:
The problem may be less about the type of source and more about how the expert selected and applied it.
A simple framework helps prevent different evidentiary issues from being blended together:
Rule 703 applies a reverse-balancing test to a narrower category of evidence than Rule 403. Under Rule 703, the probative value of otherwise inadmissible basis information in helping the jury evaluate the opinion must substantially outweigh its prejudicial effect. Rule 403, by contrast, permits exclusion when unfair prejudice, confusion, or another listed danger substantially outweighs probative value.
Unless the court orders otherwise, Rule 705 allows an expert to state an opinion and explain the reasons for it without first testifying to the underlying facts or data. The expert may still be required to disclose that information on cross-examination.
Rule 705 governs how an expert may present an opinion and when the underlying facts or data may have to be disclosed during testimony. It does not make inadmissible basis information admissible or override the disclosure limits in Rule 703.
Keeping these questions separate helps counsel frame objections more accurately.
Can an Expert Rely on Hearsay Under Rule 703?
Yes. An expert may rely on hearsay when experts in the particular field would reasonably rely on that kind of information for the opinion offered. That does not make the hearsay automatically admissible.
Can the Jury Hear Inadmissible Information Reviewed by an Expert?
Only in limited circumstances when the proponent seeks to disclose it solely under Rule 703. The proponent must show that the information’s value in helping the jury evaluate the opinion substantially outweighs its prejudicial effect. Another evidence rule may provide a separate basis for admitting the information. If otherwise inadmissible information is disclosed only to help the jury evaluate the expert’s opinion, the court must, upon a timely request, instruct the jury that the information may not be used as substantive evidence.
Does Reasonable Reliance Make an Expert Opinion Admissible?
No. The witness must be qualified, and the opinion must still satisfy Rule 702’s requirements for helpfulness, sufficient facts or data, reliable principles and methods, and reliable application. Rule 703 does not cure an analytical gap or unsupported conclusion.
Can an Expert Rely on Another Expert’s Work?
Sometimes. An expert may rely on testing, measurements, data, reports, or analysis produced by another professional when experts in the field would reasonably rely on that kind of work and the testifying expert can explain how it supports the expert’s own opinion. Problems may arise when the witness merely repeats another person’s conclusion instead of using the witness’s own expertise to form and explain an independent opinion. Courts may differ on how far this reliance may extend.
What Is a Common Rule 703 Mistake?
A common mistake is treating permission to rely on information as permission to disclose it or as proof that the opinion is reliable. Reliance, opinion admissibility, and basis disclosure require separate analyses.
Rule 703 separates two questions:
An expert may be allowed to rely on inadmissible information even when the proponent is not permitted to disclose that information to the jury.
When the proponent seeks to disclose otherwise inadmissible basis information only to help the jury evaluate the expert’s opinion, the information’s value for that purpose must substantially outweigh its prejudicial effect. This demanding standard generally favors nondisclosure.
The Rule 703 balancing test does not control information that is independently admissible for another purpose under a different evidence rule.
Rule 703 is not a hearsay exception. An expert may sometimes rely on hearsay, but that does not automatically make the hearsay admissible or allow the expert to repeat it freely to the jury.
Rule 703 addresses whether an expert may rely on particular kinds of facts or data, including otherwise inadmissible information. Rule 702 governs whether the resulting testimony has a sufficient basis, uses reliable principles and methods, reflects a reliable application, and will help the trier of fact.
The witness must also be qualified by knowledge, skill, experience, training, or education. The proponent must then show that it is more likely than not that:
Reliance on a particular kind of information may meet Rule 703’s reasonable-reliance requirement while the resulting opinion still fails Rule 702.
For example, suppose an economist relies on government wage data. The opinion may still be unreliable if the expert selects an occupation, geographic market, or period that does not fit the claim and cannot explain the choice.
Rule 703 asks whether experts in the field would reasonably rely on that kind of information. Rule 702 asks whether the resulting testimony satisfies the full standard for admissibility.
Courts often say that disputes about an expert’s work go to weight rather than admissibility. The 2023 amendment clarified that questions about a sufficient basis and reliable application must first be decided by the court under Rule 702, rather than being treated automatically as matters of weight.
Under Rule 104(a), judges must decide whether the Rule 702 requirements are met. That includes whether the testimony is based on sufficient facts or data and whether the opinion reflects a reliable application of the expert’s principles and methods.
The proponent must show that those requirements have been met under the more likely than not standard.
For example, two experts may disagree about which of two reliably applied models better fits the evidence. Once the court determines that each opinion satisfies Rule 702, that remaining disagreement may affect the weight of the testimony.
By contrast, failing to consider critical data, explain a major assumption, or apply the stated method may create an admissibility problem.
It is not enough for an expert to identify a source that professionals in the field sometimes use. The expert should be able to explain why experts in the field would reasonably rely on the information and how it supports the particular opinion under Rule 702.
In practice, concerns about the expert’s factual basis or application may appear in several forms:
A method is not unreliable simply because it was developed for litigation. Still, the expert should be able to explain how the approach was tested, checked, applied consistently, or otherwise shown to be reliable for the opinion offered.
Under Daubert, trial judges examine reliability and fit. Joiner permits scrutiny of the gap between the data and the conclusion, and Kumho Tire confirms that the same gatekeeping duty applies to technical and other specialized testimony.
Reviewing the expert’s sources before the applicable disclosure or testimony deadline may reveal problems under Rules 702 and 703, as well as issues that could surface during deposition or cross-examination.
For each important source, counsel should ask:
Counsel should also identify every material assumption and ask where it came from. Even a long source list may leave an important question unanswered: Which materials actually shaped the expert’s analysis?
Finding those weaknesses early gives counsel a chance to investigate, clarify, narrow, or otherwise address them before deposition, cross-examination, or a Rule 702 motion.
Suppose a medical causation expert reviews hospital records, imaging studies, laboratory findings, an autopsy report, and treating-physician notes.
If specialists in the field would reasonably rely on those kinds of materials when evaluating causation, Rule 703 may allow the expert to base an opinion on them even when some underlying statements or information would otherwise be inadmissible.
The proponent must still show that the opinion is based on sufficient facts or data and that the expert reliably applied the methodology to the case. When alternative causes matter to the expert’s method or conclusion, counsel should also ask how the expert considered them.
The opinion may be vulnerable if it depends heavily on a patient history that lacks adequate support, uncertain timing that materially affects causation, or another physician’s unsupported impression.
The expert may be allowed to rely on the records without being allowed to repeat everything in them to the jury.
Suppose a damages expert relies on sales records, management projections, industry reports, and government economic data to calculate lost profits.
Rule 703 may permit reliance on these types of sources if experts in the relevant field would reasonably rely on them for that analysis.
Depending on the method and facts of the case, reliability concerns may arise if the expert:
The problem may be less about the type of source and more about how the expert selected and applied it.
A simple framework helps prevent different evidentiary issues from being blended together:
Rule 703 applies a reverse-balancing test to a narrower category of evidence than Rule 403. Under Rule 703, the probative value of otherwise inadmissible basis information in helping the jury evaluate the opinion must substantially outweigh its prejudicial effect. Rule 403, by contrast, permits exclusion when unfair prejudice, confusion, or another listed danger substantially outweighs probative value.
Unless the court orders otherwise, Rule 705 allows an expert to state an opinion and explain the reasons for it without first testifying to the underlying facts or data. The expert may still be required to disclose that information on cross-examination.
Rule 705 governs how an expert may present an opinion and when the underlying facts or data may have to be disclosed during testimony. It does not make inadmissible basis information admissible or override the disclosure limits in Rule 703.
Keeping these questions separate helps counsel frame objections more accurately.
Can an Expert Rely on Hearsay Under Rule 703?
Yes. An expert may rely on hearsay when experts in the particular field would reasonably rely on that kind of information for the opinion offered. That does not make the hearsay automatically admissible.
Can the Jury Hear Inadmissible Information Reviewed by an Expert?
Only in limited circumstances when the proponent seeks to disclose it solely under Rule 703. The proponent must show that the information’s value in helping the jury evaluate the opinion substantially outweighs its prejudicial effect. Another evidence rule may provide a separate basis for admitting the information. If otherwise inadmissible information is disclosed only to help the jury evaluate the expert’s opinion, the court must, upon a timely request, instruct the jury that the information may not be used as substantive evidence.
Does Reasonable Reliance Make an Expert Opinion Admissible?
No. The witness must be qualified, and the opinion must still satisfy Rule 702’s requirements for helpfulness, sufficient facts or data, reliable principles and methods, and reliable application. Rule 703 does not cure an analytical gap or unsupported conclusion.
Can an Expert Rely on Another Expert’s Work?
Sometimes. An expert may rely on testing, measurements, data, reports, or analysis produced by another professional when experts in the field would reasonably rely on that kind of work and the testifying expert can explain how it supports the expert’s own opinion. Problems may arise when the witness merely repeats another person’s conclusion instead of using the witness’s own expertise to form and explain an independent opinion. Courts may differ on how far this reliance may extend.
What Is a Common Rule 703 Mistake?
A common mistake is treating permission to rely on information as permission to disclose it or as proof that the opinion is reliable. Reliance, opinion admissibility, and basis disclosure require separate analyses.
Federal Rules of Evidence
Federal Rules of Evidence