Case 1: The evidence must support the conclusion reached.
General Electric v. Joiner, 522 U.S. 136 (1997)
The U.S. Supreme Court Joiner held that a trial judge may exclude expert testimony when the evidence relied on by the evidence does not support the expert’s conclusion. In this case, the expert relied on animal studies in which infant mice caused cancer in mice who were exposed to massive doses of a certain chemical. Thus, the expert concluded that the plaintiff, who had been exposed to much smaller doses of the chemical, had cancer caused by the chemical. The expert also relied on four studies that were inconclusive in recognizing a link between that particular chemical and the cancer. Thus the Supreme Court held that the trial judge had not abused its discretion by excluding the expert’s testimony because the evidence he had relied on did not support the conclusion he reached.
Case 2: Daubert standards apply to all experts, not just scientific experts.
Kuhmo Tire Ltd. v. Carmichael, 526 U.S. 137 (1999)
In Kuhmo Tire, the U.S. Supreme Court held that the Daubert standards apply to all expert witnesses, including engineers and non-scientific experts. In this case, the plaintiffs relied on an expert witness, whom they characterized as a “technical” witness, to demonstrate that a tire blowout was caused by a defective tire, based on two factors related to the tire’s appearance and wear and tear. The trial court excluded his testimony on the grounds that his theory about the four tire factors was not reliable. The Supreme Court upheld the exclusion on the grounds that “it would prove difficult, if not impossible, for judges to administer evidentiary rules under which a gatekeeping obligation depended upon a distinction between ‘scientific’ knowledge and ‘technical’ or ‘other specialized’ knowledge.”
In affirming the trial court’s finding that this particular expert’s testimony was unreliable, the Court explained the following:
The particular issue in this case concerned the use of Carlson’s two-factor test and his related use of visual/tactile inspection to draw conclusions on the basis of what seemed small observational differences. We have found no indication in the record that other experts in the industry use Carlson’s two-factor test or that tire experts such as Carlson normally make the very fine distinctions about, say, the symmetry of comparatively greater shoulder tread wear that were necessary, on Carlson’s own theory, to support his conclusions. Nor, despite the prevalence of tire testing, does anyone refer to any articles or papers that validate Carlson’s approach. . . . Indeed, no one has argued that Carlson himself, were he still working for Michelin, would have concluded in a report to his employer that a similar tire was similarly defective on grounds identical to those upon which he rested his conclusion here. Of course, Carlson himself claimed that his method was accurate, but, as we pointed out in Joiner, “nothing in either Daubert or the Federal Rules of Evidence requires a district court to admit opinion evidence that is connected to existing data only by the ipse dixit of the expert.” 522 U.S., at 146, 118 S.Ct. 512.
Respondents additionally argue that the District Court too rigidly applied Daubert’s criteria. They read its opinion to hold that a failure to satisfy any one of those criteria automatically renders expert testimony inadmissible. The District Court . . . explicitly recognized that the relevant reliability inquiry “should be ‘flexible,’ ” that its “ ‘overarching subject [should be] … validity’ and reliability,” and that “Daubert was intended neither to be exhaustive nor to apply in every case.” App. to Pet. for Cert. 4c (quoting Daubert, 509 U.S., at 594–595, 113 S.Ct. 2786). And the court ultimately based its decision upon Carlson’s failure to satisfy either Daubert’s factors or any other set of reasonable reliability criteria.
Case 3: Parties should supplement their evidence with additional experts when a crucial expert is being challenged.
Weisgram v. Marley Co., 528 U.S. 440
After a trial in which the plaintiff’s entire case relied on one expert witness, the defendant was denied judgment as a matter of law and appealed to the U.S. Court of Appeals for the Eight Circuit. The appellate court considered the plaintiff’s expert and found that he was unreliable under Daubert. Excluding his testimony, the court granted judgment for the defendant, without giving the plaintiff the chance to give the plaintiff a chance to try to case again with a different expert. The plaintiff argued on appeal to the U.S. Supreme Court that this violated their right to fairness because the expert had not been excluded until after the trial. In response the Court stated the following:
Since Daubert, moreover, parties relying on expert evidence have had notice of the exacting standards of reliability such evidence must meet. 509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469; see also Kumho Tire Co. v. Carmichael, 526 U.S. 137, 119 S.Ct. 1167, 143 L.Ed.2d 238 (1999) (rendered shortly after the Eighth Circuit’s decision in Weisgram’s case);12General Electric Co. v. Joiner, 522 U.S. 136, 118 S.Ct. 512, 139 L.Ed.2d 508 (1997). It is implausible to suggest, post-Daubert, that parties will initially present less than their best expert evidence in the expectation of a second chance should their first try fail. We therefore find unconvincing Weisgram’s fears that allowing courts of appeals to direct the entry of judgment for defendants *456 will punish plaintiffs who could have shored up their cases by other means had they known their expert testimony would be found inadmissible. See Brief for Petitioner 18, 25. In this case, for example, although Weisgram was on notice every step of the way that Marley was challenging his experts, he made no attempt to add or substitute other evidence. 
In sum, the Court faulted the plaintiff for relying on only one expert witness when they had notice that the expert’s qualifications under Daubert were in question.
Case 4: Daubert Factors are neither exhaustive nor applicable to every case.
Daubert v. Merrell Dow Pharm., Inc., 43 F.3d 1311 (9th Cir. 1995)
After the Supreme Court’s decision in Daubert was remanded for further consideration, the Ninth Circuit stated the following:
We read [the Daubert] factors as illustrative rather than exhaustive; similarly, we do not deem each of them to be equally applicable (or applicable at all) in every case. Rather, we read the Supreme Court as instructing us to determine whether the analysis undergirding the experts’ testimony falls within the range of accepted standards governing how scientists conduct their research and reach their conclusions.
Considering the Daubert factors, the Court excluded the plaintiff’s experts’ testimony that a certain drug has caused a certain deformity, on the grounds that none of the experts had based their testimony on pre-existing research relevant to the litigation, that the theories underlying their conclusions were not published in peer-reviewed literature, and that their methodologies did not support the conclusions reached.
Case 5: “Good grounds” that an expert is reliable requires more than a prima facie showing of reliability
In re Paoli R.R. Yard PCB Litig., 35 F.3d 717 (3d Cir. 1994)
In In re Paoli, the plaintiffs argued that they needed to only make a prima facie showing that an expert’s testimony is reliable. The court thus clarified that a party need do more than show that an expert is qualified on his or her face. Rather they must show that there are “good grounds” to show that the expert is qualified. The court further explained the following:
This does not mean that plaintiffs have to prove their case twice—they do not have to demonstrate to the judge by a preponderance of the evidence that the assessments of their experts are correct, they only have to demonstrate by a preponderance of evidence that their opinions are reliable. . . . The evidentiary requirement of reliability is lower than the merits standard of correctness. Daubert states that a judge should find an expert opinion reliable under Rule 702 if it is based on “good grounds,” i.e., if it is based on the methods and procedures of science. A judge will often think that an expert has good grounds to hold the opinion that he or she does even though the judge thinks that the opinion is incorrect. As Daubert indicates, “[t]he focus … must be solely on principles and methodology, not on the conclusions that they generate.” Daubert, 509 U.S. at ––––, 113 S.Ct. at 2797. 
Case 6: Epidemiological evidence is very important for showing causation in toxic tort cases.
Rider v. Sandoz Pharm. Corp., 295 F.3d 1194 (11th Cir. 2002)
In order to prove that a certain drug caused strokes, the plaintiffs presented expert testimony that the court described as follows:
The scientific evidence presented by plaintiffs in support of their theory of causation may be grouped into six categories: 1) epidemiological studies that, on the whole, may point weakly toward causation; 2) case reports in which injuries were reported subsequent to the ingestion of Parlodel; 3) dechallenge/rechallenge tests that implied a relationship between Parlodel and stroke; 4) evidence that ergot alkaloids (a class of drug that includes bromocriptine) may cause ischemic stroke; 5) animal studies indicating that under some circumstances, bromocriptine may cause vasoconstriction in dogs and other animals; and, 6) the FDA statement withdrawing approval of Parlodel’s indication for the prevention of lactation. . . . Plaintiffs presented four epidemiological studies. Three of the four appear to have found no relationship or a negative relationship between Parlodel and stroke. Another may suggest a positive relationship. Nonetheless, both parties agree that none of the studies present statistically significant results and that the epidemiological evidence in this case is inconclusive.
In discussing this evidence, the court noted that it is “well-settled” that epidemiological evidence is very helpful in toxic tort cases, but that the absence thereof is not necessarily fatal to a case. Nonetheless, absent epidemiological evidence, the court found that the evidence was too “speculative” to be reliable and refused admission of the evidence under Daubert.
Case 7: Experts may testify to widely accepted scientific knowledge regardless of whether they have published about that knowledge.
Kannankeril v. Terminix International, Inc., 128 F.3d 802, 809 (3d. Cir. 1997)
An expert’s testimony about the harmful effects of organophosphates was challenged because that expert had not produced any publications on organophosphates. The Third Circuit explained the following:
Because the toxic effects of organophosphates on humans are well recognized by the scientific community, however, Dr. Gerson’s opinion is not a novel scientific theory regarding organophosphates. Instead, Dr. Gerson merely reported that Dr. Kannankeril exhibited the “signs and symptoms of chronic toxicity related to exposure to chlorpyrifos (Dursban).” Thus, although Dr. Gerson did not write on the topic, his opinion is supported by widely accepted scientific knowledge of the harmful nature of organophosphates. See also McCullock v. H.B. Fuller Co., 61 F.3d 1038, 1042 (2d Cir.1995) (holding that peer review and publication or general acceptance of an expert’s theory goes to the weight of the testimony rather than its admissibility). Based on the record before us, we conclude that Dr. Gerson’s opinion on causation has a factual basis and supporting scientific theory. Dr. Gerson based his opinion on Dr. Kannankeril’s medical records, Dr. Grober’s reports confirming her medical condition, and Terminix’s application receipts. He also relied on general experience and readings, general medical knowledge, standard textbooks, and standard references.
Case 8: Courts may decline to admit testimony based on accepted standards with unorthodox results.
Lust v. Merrell Dow Pharmaceuticals, Inc., 89 F. 3d. 594, 598 (9th Cir. 1996)
An expert purported to apply methods that were commonly practiced by other scientists, yet reached conclusions that were not reached by other scientists. After the trial court excluded the testimony, the expert’s party argued on appeal that the court had improperly focused on the conclusions rather than the methods applies. The Ninth Circuit upheld the exclusion of the testimony based on the following reasoning:
Done’s conclusions did arouse the district court’s suspicion, but that is to be expected. When a scientist claims to rely on a method practiced by most scientists, yet presents conclusions that are shared by no other scientist, the district court should be wary that the method has not been faithfully applied. It is the proponent of the expert who has the burden of proving admissibility. To enforce this burden, the district court can exclude the opinion if the expert fails to identify and defend the reasons that his conclusions are anomalous.
Case 9: Daubert requires “scientific validity” not “scientific precision”
United States v. Bonds, 12 F.3d 540 (6th Cir. 1993)
A criminal defendant challenged the method of DNA identification used by an expert in a prosecution, arguing that a different method of DNA identification would have yielded more accurate and perhaps different results. The court responded that “Daubert requires only scientific validity for admissibility, not scientific precision.” The court allowed the expert’s testimony because it satisfied the standard set forth in Daubert, regardless of whether a more accurate test might have existed.
Case 10: Expert testimony must assist trier of fact
City of Tuscaloosa v. Harcros Chemicals, Inc., 158 F.3d 548 (11th Cir. 1998)
In a case regarding an alleged conspiracy to fix prices of certain chemicals, the plaintiff’s expert testified that high losing bids as seen in that case may be signals of a conspiracy. The trial court excluded his testimony, stating that his methodology was not sound because he testified that there is no statistics test to determine that a high losing bid is a signal of a conspiracy. The Eleventh Circuit reversed this finding:
To put it succinctly, McClave’s data and testimony need not “show a successful conspiracy” to be admitted under Rule 702 as circumstantial evidence of a conspiracy. As expert evidence, the testimony need only assist the trier of fact, through the application of scientific, technical, or specialized expertise, to understand the evidence or to determine a fact in issue. As circumstantial evidence, McClave’s data and testimony need not prove the plaintiffs’ case by themselves; they must merely constitute one piece of the puzzle that the plaintiffs endeavor to assemble before the jury. 
 At 1174.
 At 1178–79.
 At 1021.
 At 1316–17.
 At 744.
 At 1198. Similar results were reached in Glastetter v. Novartis Pharm. Corp., 252 F.3d 986 (8th Cir. 2001) and Hollander v. Sandoz Pharm. Corp., 289 F.3d 1193 (10th Cir. 2002).
 At 809.
 At 598.
 At 564–65.