The Daubert standard provides a rule of evidence regarding the admissibility of expert witnesses' testimony during United States federal legal proceedings. Pursuant to this standard, a party may raise a Daubert motion, which is a special case of motion in limine raised before or during trial to exclude the presentation of unqualified evidence to the jury. The Daubert trilogy refers to the three United States Supreme Court cases that articulated the Daubert standard:
- Daubert v. Merrell Dow Pharmaceuticals, which held in 1993 that Rule 702 of the Federal Rules of Evidence did not incorporate the Frye "general acceptance" test as a basis for assessing the admissibility of scientific expert testimony, but that the rule incorporated a flexible reliability standard instead;
- General Electric Co. v. Joiner, which held that a district court judge may exclude expert testimony when there are gaps between the evidence relied on by an expert and his conclusion, and that an abuse-of-discretion standard of review is the proper standard for appellate courts to use in reviewing a trial court's decision of whether it should admit expert testimony;
- Kumho Tire Co. v. Carmichael, which held in 1999 that the judge's gatekeeping function identified in Daubert applies to all expert testimony, including that which is non-scientific.
Important appellate-level opinions that clarify the standard include Judge Kozinski's opinion in Daubert on remand (Daubert v. Merrell Dow Pharmaceuticals, Inc., 43 F.3d 1311 (9th Cir. 1995)), and Judge Becker's opinion in In re Paoli R.R. Yard PCB Litig., 35 F.3d 717 (3d Cir. 1994).
In Daubert, seven members of the Court agreed on the following guidelines for admitting scientific expert testimony:
- Judge is gatekeeper: Under Rule 702, the task of "gatekeeping", or assuring that scientific expert testimony truly proceeds from "scientific knowledge", rests on the trial judge.
- Relevance and reliability: This requires the trial judge to ensure that the expert's testimony is "relevant to the task at hand" and that it rests "on a reliable foundation". Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579, 584-587. Concerns about expert testimony cannot be simply referred to the jury as a question of weight. Furthermore, the admissibility of expert testimony is governed by Rule 104(a), not Rule 104(b); thus, the Judge must find it more likely than not that the expert's methods are reliable and reliably applied to the facts at hand.
- Scientific knowledge = scientific method/methodology: A conclusion will qualify as scientific knowledge if the proponent can demonstrate that it is the product of sound "scientific methodology" derived from the scientific method.
- Factors relevant: The Court defined "scientific methodology" as the process of formulating hypotheses and then conducting experiments to prove or falsify the hypothesis, and provided a nondispositive, nonexclusive, "flexible" set of "general observations" (i.e. not a "test")  that it considered relevant for establishing the "validity" of scientific testimony:
- Empirical testing: whether the theory or technique is falsifiable, refutable, and/or testable.
- Whether it has been subjected to peer review and publication.
- The known or potential error rate.
- The existence and maintenance of standards and controls concerning its operation.
- The degree to which the theory and technique is generally accepted by a relevant scientific community.
In 2000, Rule 702 was amended in an attempt to codify and structure elements embodied in the "Daubert trilogy." The rule then read as follows:
Rule 702. Testimony by Experts
If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise, if (1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case.
(As amended Apr. 17, 2000, eff. Dec. 1, 2000.)
In 2011, Rule 702 was again amended to make the language clearer. The rule now reads:
RULE 702. TESTIMONY BY EXPERT WITNESSES
A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if:
(a) The expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue;
(b) The testimony is based on sufficient facts or data;
(c) The testimony is the product of reliable principles and methods; and
(d) The expert has reliably applied the principles and methods to the facts of the case.
(As amended Apr. 17, 2000, eff. Dec. 1, 2000; Apr. 26, 2011, eff. Dec. 1, 2011)
While some federal courts still rely on pre-2000 opinions in determining the scope of Daubert, as a technical legal matter any earlier judicial rulings that conflict with the language of amended Rule 702 are no longer good precedent.
Although the Daubert standard is now the law in federal court and over half of the states, the Frye standard remains the law in some jurisdictions including California, Florida, Illinois, Maryland, New York, New Jersey, Pennsylvania, and Washington.
Florida has recently passed a bill to adopt the Daubert standard as the law governing expert witness testimony. The bill remains to be signed by the Governor.
Although trial judges have always had the authority to exclude inappropriate testimony, prior to Daubert, trial courts often preferred to let juries hear evidence proffered by both sides. Once certain evidence has been excluded by a Daubert motion because it fails to meet the relevancy and reliability standard, it will likely be challenged when introduced again in another trial. Even though a Daubert motion is not binding to other courts of law, if something was found untrustworthy by one court, other judges may choose to follow that precedent. Of course, a decision by the Court of Appeals that a piece of evidence is inadmissible under Daubert would be binding on district courts within that court's jurisdiction.
Daubert motion: timing 
To attack expert testimony as inadmissible, counsel may bring pretrial motions, including motions in limine. The motion in limine may be brought prior to trial, although counsel may bring the motion during trial as well.
A motion attacking expert testimony should be brought within a reasonable time after the close of discovery if the grounds for the objection can be reasonably anticipated. The hearing should be made well in advance of the first time a case appears on a trial calendar.
In one case where a Daubert hearing was conducted on the day of the trial, in which the district court excluded all plaintiff's expert testimony, resulting in the dismissal of all claims, the appellate court remanded the case because of multiple irregularities and a defective record of lower court proceedings.
The appellate court noted that in cases that rely heavily on expert testimony, a district court should set a discovery and trial schedule that realistically provides both sides with an adequate opportunity to introduce necessary evidence. The application of Federal Rule of Evidence 702 to proposed expert testimony can often be an uncertain process, and is best conducted in such a manner that litigants have a reasonable opportunity to locate experts who meet the rule's requirements.
In another case in which the defendant was apparently at fault for filing a motion to exclude expert testimony one week before the trial date, the district court denied the motion on that ground, but it advised the defendant that it might conduct its own voir dire of the expert in question before he testified. The district court preliminarily found that defendant's motion was predicated on a ruling made almost three months earlier by a district court in another state, and that defendant had shown no good cause for waiting to file the motion. The defendant ultimately lost that case, following the admission of the disputed expert testimony, and ultimately failed in its appeal.
An evidentiary hearing on the motion may not be necessary if the court finds that it would not assist the court in ruling on any of the matters in the motion.
Prior to Daubert, relevancy in combination with the Frye test were the dominant standards for determining the admissibility of scientific evidence in Federal courts. Frye is based on a 1923 Federal Court of appeals ruling involving the admissibility of polygraph evidence. Under Frye, the Court based the admissibility of testimony regarding novel scientific evidence on whether it has "gained general acceptance in the particular field in which it belongs." The trial court's gatekeeper role in this respect is typically described as conservative, thus helping to keep pseudoscience out of the courtroom by deferring to those in the field.
In Daubert, the Supreme Court ruled that the 1923 Frye test was superseded by the 1975 Federal Rules of Evidence, specifically Rule 702 governing expert testimony. Rule 702 originally stated (in its entirety),
- "If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise."
In Daubert, the Court ruled that nothing in the Federal Rules of Evidence governing expert evidence "gives any indication that 'general acceptance' is a necessary precondition to the admissibility of scientific evidence. Moreover, such a rigid standard would be at odds with the Rules' liberal thrust and their general approach of relaxing the traditional barriers to 'opinion' testimony."
By requiring experts to provide relevant opinions grounded in reliable methodology, proponents of Daubert were satisfied that these standards would result in a fair and rational resolution of the scientific and technological issues which lie at the heart of product liability adjudication.
Ironically, Daubert has not appeared to further the Federal Rules philosophy of admitting generally all relevant testimony, and specifically of relaxing the traditional barriers to 'opinion' testimony." The Daubert decision has instead been heralded by some political commentators as one of the most important Supreme Court decisions in imposing higher barriers for toxic tort and product liability cases, by allegedly reducing the volume of so-called junk science in the court room.
According to a 2002 RAND study, post Daubert, the percentage of expert testimony by scientists that was excluded from the courtroom significantly rose. This rise likely contributed to a doubling in successful motions for summary judgment in which 90% were against plaintiffs. Beyond this study, there is little empirical evidence of the impact of Daubert. However, some critics argue that Daubert has disrupted the balance between plaintiffs and defendants, “The exclusion of expert testimony affects plaintiffs far more than defendants because plaintiffs may then not be able to meet their required burden of proof. Furthermore, there is little point in plaintiffs going to the expense of Daubert motions to exclude defendant’s experts until they know if their case will proceed. So if more experts are now being excluded, then Daubert has undoubtedly shifted the balance between plaintiffs and defendants and made it more difficult for plaintiffs to litigate successfully.” Similarly, Daubert hearings can be subject to various abuses by attorneys attempting to bolster a weak case. These tactics can range from simply attempting to delay the case to driving up the costs of the litigation forcing settlement.
A different pattern has emerged in criminal cases. In criminal cases, the prosecution has the burden of proof and uses a host of forensic science methods as evidence to prove their case. But, Daubert motions are rarely made by criminal defendants and when they do, they lose a majority of the challenges. Some critics of the use of unreliable science in court argue that Daubert has had beneficial effects in civil litigation, but fails to address the underlying pathologies of the forensic science system that leads to dubious verdicts in criminal cases.
Some commentators believe that Daubert caused judges to become—in the phrase used in former Chief Justice William Rehnquist’s dissent in Daubert—amateur scientists, many lacking the scientific literacy to effectively fulfill their role as gatekeeper of scientific evidence. Although “science for judges” forums have emerged in the wake of Daubert in order to educate judges in a variety of scientific fields, many are still skeptical about the usefulness of the Daubert standard in discerning valid science. The responsibility to assess scientific relevance has shifted from highly-trained expert witnesses to judges deficient in science education. The "Daubert" ruling furthermore admits the possible introduction of non-peer reviewed data and conclusions. This increasingly shifts the burden of scientific judgement onto judges who have not had an education which would enable them to properly evaluate such data.
Pursuant to Rule 104(a), in Daubert the U.S. Supreme Court suggested that the following factors be considered:
- Has the technique been tested in actual field conditions (and not just in a laboratory)? [e.g. fingerprinting has been extensively tested and verified not only in laboratory conditions, but even in actual criminal cases. So it is admissible. Polygraphy on the other hand has been well tested in laboratories but not so well tested in field conditions]
- Has the technique been subject to peer review and publication?
- What is the known or potential rate of error?
- Do standards exist for the control of the technique's operation? [e.g. the use of penile plethysmography for sex offender risk assessment is being used by different workers according to their own standards. Thus penile plethysmography does not meet Daubert criteria]
- Has the technique been generally accepted within the relevant scientific community? [this test was earlier the only relevant criterion under Frye]
The Supreme Court explicitly cautioned that the Daubert list should not be regarded by judges as “a definitive checklist or test...” Yet in practice, judges have judged the admissibility of scientific evidence using the "Daubert factors" as a checklist; for example, the trial court judge in Kumho admitted to erroneously treating the factors as mandatory.
International influence 
The Canadian Supreme Court has expressly adopted the Daubert standard in two cases. R. v. Mohan,; R. v. J.L.-J., . In J.L.-J., the Court took a look at the development of U.S. law in this regard, noted the U.S. Supreme Court's reject of the Frye standard and its replacement with the Daubert Standard. While the Court did note that: " Daubert must be read in light of the specific text of the Federal Rules of Evidence, which differs from our own procedures," the Court also stated in the same sentence that "the U.S. Supreme Court did list a number of factors that could be helpful in evaluating the soundness of novel science.". The Court then applied the Daubert standard to a decision of the Quebec Court of Appeals. The Quebec Court had held that greater liberality should be applied by the Court in receiving pro-defense scientific evidence in a criminal case. The Court rejected this decision and reinstated the defendant's conviction.
Additionally, in 2005, the United Kingdom House of Commons Science and Technology Committee recommended the creation of a Forensic Science Advisory Council to regulate forensic evidence in the UK and observed that:
The absence of an agreed protocol for the validation of scientific techniques prior to their being admitted in court is entirely unsatisfactory. Judges are not well-placed to determine scientific validity without input from scientists. We recommend that one of the first tasks of the Forensic Science Advisory Council be to develop a “gate-keeping” test for expert evidence. This should be done in partnership with judges, scientists and other key players in the criminal justice system, and should build on the US Daubert test.
The Law Commission for England and Wales has proposed a consultation paper (No.190) to adopt a criterion like the Daubert Standard to help reform the law of evidence in regards to the admissibility of scientific evidence.
See also 
- 522 U.S. 136 (1997)
- 526 U.S. 137 (1999)
- Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993) 509 U.S. 579, 589.
- Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 593 (1993)
- Giannelli & E. Imwinkelried, Scientific Evidence §§ 1.06, 1.16 (4th ed. 2007).
- Stephen Mahle, Florida Legislature Adopts Daubert Standard for Expert Testimony
- Berger, Margaret A. (2005). "What Has a Decade of Daubert Wrought" (PDF). American Journal of Public Health. 95(S1): S59–65. doi:10.2105/AJPH.2004.044701. PMID 16030340. Retrieved 2006-07-12.
- The third circuit has emphasized the importance of conducting in limine hearings under Fed. R. Evid. 104 (resolution of preliminary questions) when making reliability determinations required by Fed. R. Evid. 702 and Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 113 S. Ct. 2786, 125 L. Ed. 2d 469 (1993). See Padillas v. Stork-Gamco, Inc., 186 F.3d 412, 417 (3d Cir. 1999) ; Voilas v. General Motors Corp., 73 F. Supp. 2d 452, 455 (D.N.J. 1999) (not holding hearing in this case, however). See also 1 Weinstein's Federal Evidence, Ch. 104, Preliminary Questions (Matthew Bender 2d ed.); Edward J. Imwinkelried & David A. Schlueter, Federal Evidence Tactics, Ch. 1, Article I: General Provisions, § 1.04 (Matthew Bender).
- See, e.g., Smoot v. Mazda Motors of America, Inc., 469 F.3d 675, 676 (7th Cir. 2006) (case dismissed after plaintiff expert's testimony excluded); Curtis v. M&S Petroleum, Inc., 174 F.3d 661, 667 (5th Cir. 1999) ; United States v. Nichols, 169 F.3d 1255, 1265-1266 (10th Cir. 1999 ); Heller v. Shaw Indus., Inc., 167 F.3d 146, 155, 157-158 (3d Cir. 1999) ; Ruiz-Troche v. Pepsi Cola of Puerto Rico, 161 F.3d 77, 90 (1st Cir. 1998) ; Jack v. Glaxo Wellcome Inc., 239 F. Supp. 2d 1308, 1319 (D. Ga. 2002) (rejecting objection of untimeliness of motion in limine to exclude expert testimony on ground that motion in limine is not dispositive); United States v. Lester, 234 F. Supp. 2d 595, 597-598 (E.D. Va. 2002) (criminal defendant's motion to allow expert testimony regarding reliability of eyewitness testimony denied); Lentz v. Mason, 32 F. Supp. 2d 733, 737 (D.N.J. 1999).
- See, e.g., Pineda v. Ford Motor Co., 520 F.3d 237, 241-242 (3d Cir. 2008) (after deposition of plaintiff's expert, defendant filed alternative motions to exclude testimony of plaintiff's expert and for summary judgment, and motion for Daubert hearing).
- Webster v. Fulton County, Ga., 85 F. Supp. 2d 1375, 1377 (N.D. Ga. 2000) (denying defendant's Daubert motion as untimely, when brought after court had relied on plaintiff expert's report in denying defense summary judgment motion, and within days of trial date). See also Alfred v. Caterpillar, Inc., 262 F.3d 1083, 1087 (10th Cir. 2001 ) (counsel should not sandbag Daubert concerns until close of opponent's case; however, appellate court did not reach issue of late filing of motion because district court chose to address defendant's Daubert objections on merits, rather than deeming them waived); Pullman v. Land O'Lakes, Inc., 262 F.3d 759, 763 (8th Cir. 2001) (appellate court noted with disapproval that defendant failed to bring Daubert motion until shortly before the trial began; Daubert inapplicable to experimental test evidence not presented by expert witnesses).
- See Smith v. Ford Motor Co., 215 F.3d 713, 722 (7th Cir. 2000) . See also Goebel v. Denver and Rio Grande W. R.R., 215 F.3d 1083, 1087 (10th Cir. 2000) (district court orally denied motion to exclude expert testimony on morning of trial); McPike v. Corghi S.p.A., 87 F. Supp. 2d 890, 891 n.1 (E.D. Ark. 1999) (court telephoned attorneys with ruling denying defendant's motion to exclude plaintiff's expert testimony, because closeness of trial did not allow time for formal written memo and order at that time; court later rendered substituted memorandum and order, fully stating reasons for its decision in writing).
- See Clay v. Ford Motor Co., 215 F.3d 663, 674 (6th Cir. 2000)
- Frye v. United States, 293 F. 1013 (DC Cir. 1923)
- Owen, D. G. (2002). "A Decade of Daubert". Denver University Law Review 80: 345. ISSN 0883-9409.
- Dixon, L, Gill B. Changes in the Standards for Admitting Expert Evidence in Federal Civil Cases Since the Daubert Decision. RAND Institute for Civil Justice. 2002.
- Gutheil, Thomas G.; Bursztajn, Harold J. (1 June 2005). "Attorney Abuses of Daubert Hearings: Junk Science, Junk Law, or Just Plain Obstruction?". Journal of the American Academy of Psychiatry and the Law 33 (2): 150–152. PMID 15985655.
- Risinger, D. Michael (2000). "Navigating Expert Reliability: Are Criminal Standards of Certainty Being Left on the Dock?". Albany Law Review 64: 99. ISSN 0002-4678.
- Neufeld, P. (2005). "The (Near) Irrelevance of Daubert to Criminal Justice and Some Suggestions for Reform". American Journal of Public Health 95 (S1): S107–S113. doi:10.2105/AJPH.2004.056333. PMID 16030325.
- Bernstein, David E. (2007). "Expert Witnesses, Adversarial Bias, and the (Partial) Failure of the Daubert Revolution". Iowa Law Review. SSRN 963461.
- Gatowski, S. I. et al. (2001). "Asking the gatekeepers: A National Survey of Judges on Judging Expert Evidence in a Post-Daubert world". Law and Human Behavior 25 (5): 433–458. doi:10.1023/A:1012899030937.
- Rothman, K. J.; Greenland, S. (2005). "Causation and Causal Inference in Epidemiology". American Journal of Public Health 95 (S1): S144–S150. doi:10.2105/AJPH.2004.059204. PMID 16030331.
- Melnick, R. (2005). "A Daubert Motion: A Legal Strategy to Exclude Essential Scientific Evidence in Toxic Tort Litigation". American Journal of Public Health 95 (S1): S30–S34. doi:10.2105/AJPH.2004.046250. PMID 16030335.
- Jasanoff, S. (2005). "Law's Knowledge: Science for Justice in Legal Settings". American Journal of Public Health 95 (S1): S49–S58. doi:10.2105/AJPH.2004.045732. PMID 16030338.
- "The admissibility of scientific evidence in psychiatric malpractice: junk science and the Daubert case". J Clin Forensic Med 1 (3): 145–8. December 1994. doi:10.1016/1353-1131(94)90082-5. PMID 16371283. Unknown parameter
- See (c) of the syllabus of the Daubert case.
-  2 S.C.R. 9
- 2 S.C.R. 600
-  R.J.Q. 2229, 130 C.C.C. (3d) 541,  Q.J. No. 2493 (QL).
- House of Commons Science and Technology Committee (2005) Forensic Science on Trial, London: The Stationery Office Limited, HC96-I, para.173
- The Admissiblity of Expert Evidence in Criminal Proceedings in England and Wales (PDF)
- The Daubert Trilogy in the States
- Daubert on the Web
- Daubert-The Most Influential Supreme Court Decision You've Never Heard Of
- Project on Scientific Knowledge and Public Policy (SKAPP), collection of original documents and commentary on the Daubert standard and the use of science in public policy.
- Daubert Institute for Science & Law How Daubert applies to psychiatric and psychological evidence.
- The Partial Failure of the Daubert Revolution
- Barry Yeoman Putting Science in the Dock, The Nation
- The Daubert Tracker