Full opinion text
TABLE OF CONTENTS I. INTRODUCTION 782 II. FACTS AND PROCEDURAL HISTORY 734 III. SUBJECT MATTER JURISDICTION OF THE DISTRICT COURT 737 IV. WAS THE IN LIMINE HEARING TAINTED BY UNFAIR PROCEDURES? 738 A. Inadequate Opportunity to Depose Defense Experts 738 B. Exclusion of Opinion of Experts for Whom No. 26(b)(4) Statements Were Filed 739 V. LEGAL STANDARDS FOR THE ADMISSIBILITY OF EXPERT OPINION 741 A. Rule 702 741 1. Qualifications 741 2. Reliability 742 3. Fit 742 4. The roles of judge and jury: how high a threshold for reliability? 743 5. Confusion — Rules 702 and 403 746 6. Procedural concerns regarding the Rule 403/702 balancing test 747 B. Rule 703 747 C. Standard of Review 749 D. The Significance of Pennsylvania’s Requirement of Reasonable Medical Certainty 750 VI. THE RELATIONSHIP BETWEEN PCBs AND PLAINTIFFS’ ILLNESSES 752 A. Dr. Sherman’s Qualifications 753 B. Rule 703 and Dr. Sherman’s Immunological Tests 754 C. Adequacy of Dr. Sherman’s and Dr. DiGregorio’s Use of Differential Diagnosis in Evaluating Causation of Present Illnesses 755 1. The district court’s critique 755 2. The plaintiffs’ response 757 3. Rule 702 analysis 758 a. The opinions of Dr. DiGregorio 763 b. The opinions of Dr. Sherman 764 i. Bessie Cunningham 765 ii. Amber Burrell 766 iii. Priscilla Burrell 767 iv. Monica Hilton 768 v. Matthew Cunningham 768 vi. Patricia Ingram 769 vii. John Ingram, Sr. 769 viii. John Ingram, Jr. 769 ix. George Burrell 769 x. Wallace Cummins 769 xi. April Ingram 770 xii. The Remaining Plaintiffs 770 c. Rule 403 770 d. Summary (DiGregorio and Sherman) 770 VII. EXPOSURE — THE OPINION OF IAN C.T. NISBET, Ph.D. 771 A. Recalculation of the AML Data 772 B. Recalculation of Background 773 C. Back Calculations 774 D. Remaining Issues 778 E. Conclusion 778 VIII. THE HARMFULNESS OF THE CHEMICALS 778 A. Introduction 778 B. Animal Studies 779 C. Exposure to Dioxins and Furans 781 IX. THE YUSHO AND YU CHENG INCIDENTS 783 X.THE PLAINTIFFS’ PERSONAL INJURY CLAIMS — SUMMARY AND CONCLUSION 784 XI. THE MEDICAL MONITORING CLAIMS 785 A. Medical Monitoring as a Viable Claim 785 B. The Medical Monitoring Test Restated 787 C. Application of the Test 788 1. Admissibility of plaintiffs’ evidence 789 a. Dr. Sherman’s testimony 789 b. Dr. DiGregorio’s testimony 790 i. Reliability 790 ii. Failure to comply with the scheduling order 791 c. Dr. Sehecter’s testimony 793 2. Summary judgment on medical monitoring 793 XII. PROPERTY DAMAGE 795 XIII. CONCLUSION 798 Before BECKER, ROTH, and LEWIS, Circuit Judge. OPINION OF THE COURT BECKER, Circuit Judge. I. INTRODUCTION The plaintiffs in this toxic tort case have lived for many years in the vicinity of the Paoli Railyard, a railcar maintenance facility at which polychlorinated biphenyls (PCBs) were used in profusion for over a quarter century. They have sued to recover damages for a variety of physical ailments and for property damage against the corporations that have maintained the railyard and that sold the PCBs. This appeal is from the district court’s second grant of summary judgment for the defendants. In In re Paoli R.R. Yard PCB Litig., 916 F.2d 829 (3d Cir.1990) (“Paoli I”), cert. denied, 499 U.S. 961, 111 S.Ct. 1584, 113 L.Ed.2d 649 (1991), we reversed the grant of summary judgment for defendants and remanded for further proceedings. We did so because the foundation of the summary judgment — the exclusion of virtually all the plaintiffs’ expert opinion pursuant to Federal Rules of Evidence 702, 703 and 403 — was undermined by (1) the failure of the district court to permit sufficient development of the record upon which a determination to exclude expert evidence might be based, and (2) the district court’s failure to make findings, grounded on Fed.R.Evid. 702 or 703, setting forth the basis of its decision. On remand the district court conducted five days of in limine hearings, receiving extensive evidence about the scientific reliability of plaintiffs’ expert opinions. It then filed extensive opinions (totalling 330 pages) setting forth not only findings of fact but also its reasons for again excluding the vast bulk of plaintiffs’ expert evidence. This appeal followed. Resolution of the appeal requires that we address myriad issues of procedure, evidence, and substantive law. Primarily, however, we must consider the voluminous record concerning expert opinion and, applying Fed.R.Evid. 702 and the standards enunciated by the Supreme Court in Daubert v. Merrell Dow Pharm., Inc., — U.S. —, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993), decide whether the district court erred in again excluding the opinions of plaintiffs’ experts in connection with its summary judgment determination. Daubert requires the district court to act as “gatekeeper” and to assure that the scientific methodology upon which the expert opinion is founded is reliable, i.e., that the expert’s conclusion is based on good grounds (the methods and principles of science). We also must deal with Fed.R.Evid. 703 because the district court’s exclusion of expert testimony rests, in part, on its conclusion that some of the hearsay evidence upon which the experts relied is not of a kind usually relied on by experts in the field. In this regard.we conclude that the precept announced in In re: Japanese Electronics Prod. Antitrust Litig., 723 F.2d 238 (3d Cir. 1983), rev’d on other grounds sub nom., Matsushita Electric. Indus. Co. v. Zenith Radio Corp., 475 U.S. 574, 106 S.Ct. 1348, 89 L.Ed.2d 538 (1986), that the principal arbiters of the reasonableness of reliance upon inadmissible evidence are the experts and not the trial judge, does not survive Daubert. Preliminary to an application of Rules 702-703 to the evidentiary rulings at issue, we must address the question of the proper scope of review. Although review of the district court’s fact findings that undergird its rulings on the admissibility of expert opinion is deferential, given the enormous power of the district court to foreclose submission of a party’s case to a jury on the basis of a threshold determination of nonreliability of opinion evidence, we conclude that the review requires a “hard look” to insure that the district court’s exercise of discretion was sound and that it correctly applied the several Daubert factors. Then to the extent that any of the expert opinion survives, we must determine whether the plaintiffs can avoid summary judgment on any of the claims to which the surviving opinion pertains. For the most part we will affirm the rulings and the judgment of the district court. However, we also will reverse in part, and remand some claims for trial. In summary we rule as follows. 1. We will affirm the district court’s decision to retain jurisdiction in this case based on pendent jurisdiction stemming from the plaintiffs’ prior CERCLA claims. 2. We will affirm the district court’s discretionary ruling allowing certain of defendants’ experts to testify at the in limine hearings without being deposed; however, we point out that depositions should generally be afforded in future cases of this nature. We do not reach the propriety of its decision excluding plaintiffs’ experts for whom no Rule 26(b)(4) statements were filed because plaintiffs do not rely on these experts in opposition to summary judgment. 3. We will reverse the district court’s exclusion of the opinion of Dr. Janette D. Sherman insofar as it was grounded on the conclusion that she was an unqualified expert. However, we affirm the district court’s holding that she could not rely on immunological tests from an unaccredited laboratory. We also affirm the district court’s exclusion of the opinions of Dr. Sherman as to causation of plaintiffs’ present injuries with respect to those plaintiffs whom she did not examine and whose medical history she did not take. We believe that, in the absence of employment of the standard techniques of differential diagnosis, and in the absence of any good explanation justifying her conclusion in the light of possible alternative causes of plaintiffs’ injuries, Dr. Sherman’s methodology as to those plaintiffs was not reliable, as the district court found. 4. We will affirm the district court’s exclusion of the opinion of Dr. G. John DiGre-gorio with respect to causation of the injuries of those plaintiffs for whom he testified. Because Dr. DiGregorio neither examined these plaintiffs nor took their medical histories, he did not have a reliable basis from which to conclude they were ill. Moreover, as with Dr. Sherman, in the absence of employment of standard techniques of differential diagnosis, and failure to provide any explanation as to why he concluded that PCBs rather than alternative possibilities had caused plaintiffs’ illnesses, we conclude that Dr. DiGregorio’s assessment of causation was unreliable. 5. We will reverse the district court’s exclusion from evidence of the opinions of Dr. Sherman with respect to most of the injuries of Bessie Cunningham and Amber Burrell, whom she actually examined and whose medical histories she took. In light of: (1) Dr. Sherman’s employment of the standard techniques of differential diagnosis with respect to those plaintiffs, and (2) defendants’ failure to point to possible alternative causes of their injuries which Dr. Sherman failed to consider, we are satisfied that, with respect to them, Dr. Sherman’s scientific methodology was reliable and that the district court’s exclusion of her opinion represented an impermissible jury-like determination that it preferred the defendants’ experts’ opinion to that of Dr. Sherman. 6. We will affirm the district court’s ex-elusion from evidence of the opinion of Dr. Ian Nisbet regarding plaintiffs’ exposure to PCBs: (1) insofar as that opinion is based on a recalculation of American Medical Laboratory test (“AML”) results to account for the degree to which the laboratory ostensibly underestimated its results; and (2) insofar as it is grounded on “back calculations” of plaintiffs’ PCB blood levels in 1986 based upon the results of studies made by the Eco Logic laboratory in 1992. We conclude that Dr. Nisbet’s methodology in recalculating the AML tests was unreliable, and that the Eco Logic data from which he began his back calculations was not a type reasonably relied on by experts in the field due to the quality control problems in Eco Logic’s methodology- 7. We will reverse the district court’s exclusion of the remainder of Dr. Nisbet’s opinion, including his conclusion that plaintiffs had PCBs in their blood at levels above the background PCB levels in the general population. We are satisfied that Dr. Nisbet’s calculation of background blood levels from National Human Adipose Tissue Survey (“NHATS”) fat data was based on a reliable methodology, and that the NHATS data was a type of data reasonably relied on by experts. 8. We will reverse the district court’s exclusion of animal studies. Where, as here, these studies were supported by some epidemiological data and had been used by EPA to conclude that PCBs were a probable human carcinogen, plaintiffs’ experts had good grounds for determining that they “fit” a conclusion regarding human causation. 9. We will affirm the district court’s exclusion of data on chemicals other than PCBs and its exclusion of testimony related to the incidents at Yusho (in Japan) and Yu Cheng (in Taiwan). The district court’s conclusion under Fed.R.Evid. 403 that the probative value of this evidence would have been substantially outweighed by unfair prejudice (and would have resulted in significant waste of trial time for resolution of collateral issues) was based on a more than adequate record (one justifying the rare making of the pretrial ruling based on Rule 403), and on findings of fact which, under the applicable standard of review we cannot disturb. 10. We will reverse the grant of summary judgment with respect to those personal injury plaintiffs for whom Dr. Sherman’s testimony is admissible, concluding that they have demonstrated the existence of a genuine issue of material fact as to whether defendants exposed them to PCBs which caused their present injuries. 11. We will reverse the grant of summary judgment with respect to the medical monitoring claims. Although recent changes in Pennsylvania law have interred plaintiffs’ increased risk claims, we still believe that the Pennsylvania Supreme Court would recognize the plaintiffs’ medical monitoring claims, and are satisfied that Dr. Sherman’s testimony as to the plaintiffs’ future risk is sufficient to get them over the summary judgment threshold. 12. We will reverse the grant of summary judgment on plaintiffs’ claim with respect to diminution in property value. Based on an extrapolation from existing Pennsylvania case law, we predict that where (1) the defendants have caused some physical harm to plaintiffs’ property; (2) repair of this damage will not restore the value of the property to its prior level; and (3) there is at least some ongoing risk to the plaintiffs’ land, Pennsylvania would allow plaintiffs to recover damages for the diminution of their property value. On the present record, there remains a genuine issue of material fact on the permanency of damage issue. 13. With respect to all other claims, which represent the bulk of plaintiffs’ ease, the exclusion of the expert opinion leaves the plaintiffs with inadequate evidence to survive summary judgment. We will therefore affirm the grant of summary judgment on these remaining claims. II. FACTS AND PROCEDURAL HISTORY Beginning in the 1950s, if not before, PCBs were used at the Paoli Railroad Yard (the ‘Yard”) as a fire-resistant insulating fluid in railroad car transformers. PCBs gradually accumulated in the Yard and leaked off the Yard into groundwater and ultimately into the soil of nearby residences. ([ AXXXX-XXXX ]). Several studies from 1979-1986 documented high levels of PCBs in the Yard and in nearby water and land. The National Institute for Occupational Safety and Health (NIOSH) identifies the site as containing the worst PCB contamination it has ever encountered during a health inspection. In 1986, the United States sued SEPTA, Conrail and Amtrak under the Comprehensive Environmental Response Compensation and Liability Act (CERCLA), 42 U.S.C. § 9601, to compel the cleanup of the Yard. After the entry of five consent decrees, which primarily required the control of leakage from the Yard, EPA adopted a final plan, the Record of Decision, in July of 1992. This plan requires extensive excavation and treatment of soils both at the Yard and on nearby, residential property and streams, and erosion controls at the Yard. The plaintiffs in this action consist of individuals who lived near the Yard in areas identified by EPA and by the railroad defendants’ contractor, Groundwater Technologies, Inc., as having experienced the most severe run-off from the Yard. The plaintiffs have adduced evidence of significant levels of PCBs in the soil at their homes. Many of the plaintiffs played in the soil at their homes while growing up, gardened in it, and ate vegetables grown from it. Many also regularly traversed the Yard on foot as a' short cut to their destinations. In 1986, thirty eight plaintiffs brought suit in the District Court for the Eastern District of Pennsylvania. Some sought recovery for present injuries, (allegedly caused by exposure to PCBs and other assorted chemicals from the Yard, including polychlorinated dibenzo furans (“furans”) and polychlorinated dibenzo-p-dioxins (“dioxins”)). Some plaintiffs, many of whom have not yet suffered any physical injury, brought claims for emotional distress caused by fear of future injury, and for medical monitoring to decrease the likelihood of the future development of serious diseases. Finally, some of the plaintiffs have brought claims for the decrease in value to their property caused by the presence of PCBs on the land. The defendants (in some or all of the cases) are Monsanto Corporation, the nation’s leading manufacturer of PCBs; General Electric Company, manufacturer of some of the railroad car transformers in which the PCBs were used; Amtrak, owner of the Yard since 1976; Conrail, which operated the facility between 1976 and 1983; the Southeastern Pennsylvania Transit Authority (SEPTA), which has operated the facility since 1983; and the City of Philadelphia, which is linked with SEPTA. SEPTA filed third-party complaints against Westinghouse Electric Corporation, manufacturer of some of the transformers used at the Yard, and the Budd Company, manufacturer of some of the railroad ears. Conrail filed a third part complaint against the Penn Central Corporation. In November of 1988 the district court granted defendants’ motion for summary judgment against all plaintiffs on the personal injury claims because it held that all of plaintiffs’ evidence pertaining to significant exposure and causation, necessary elements of their claims, was inadmissible. The court excluded the evidence under Federal Rule of Evidence 702, which requires expert witnesses to be qualified and to use reliable scientific techniques, Rule 703 which requires experts to rely on data of a type reasonably relied upon by experts in the field, and Rule 403 which requires the probative value of evidence not to be substantially outweighed by unfair prejudice or undue delay. See In re Paoli R.R. Yard PCB Litig., 706 F.Supp. 358 (E.D.Pa.1988). In Paoli I, 916 F.2d at 854, this Court reversed the Rule 703 holdings because the district court had not created a sufficiently detailed factual record on which to base them and had not given “the plaintiffs sufficient opportunity to explore the issues upon which they were ultimately denied relief.” We reversed the district court’s Rule 702 holdings because it had construed the qualification requirement of Rule 702 too strictly, see id. at 855-56, and because it had not created a detailed enough factual record to justify exclusion of the experts’ opinion under the reliability prong of Rule 702. See id. at 858-59. Finally, we reversed the district court’s Rule 403 determinations, holding that Rule 403 exclusions should not be granted pretrial absent a record which is “a virtual surrogate for a trial record.” Id. at 859-60. We strongly suggested that the district court should have held an in limine hearing before excluding plaintiffs’ expert opinion. Id. at 859. Following remand, the district court issued a cáse management order in June 1991, giving plaintiffs until March 2, 1992 to complete their discovery, and until March 17, 1992 to designate their trial experts and provide defendants with their experts’ reports. The court required the defendants to do likewise one month after plaintiffs. The list of expert witnesses designated by the plaintiffs in March of 1992 was considerably different from the list at the time of the 1988 summary judgment. The twenty-three plaintiffs represented by the Kohn, Nast, & Graf, and Klehr, Harrison, Harvey, Branz-burg, Ellers, & Weir law firms (the “Kohn/Klehr” plaintiffs) named three experts supporting their personal injury claims: Mel-vyn Kopstein, Ph.D., to testify about the Paoli residents’ opportunities for exposure to PCBs from the Yard; Ian C.T. Nisbet, Ph. D., to testify about the plaintiffs’ exposure to PCBs; and Janette Sherman, M.D., to testify that PCBs had caused plaintiffs’ injuries and that plaintiffs require medical monitoring to detect and treat future PCB-related illnesses. Defendants moved in limine to exclude the opinions of each of these experts under Fed.R.Evid. 702, 703 and 403. On the same grounds, defendants filed motions in limine to preclude the plaintiffs’ experts from testifying about animal studies purporting to show the harmful effects of PCBs, evidence concerning the harm of dioxins and furans (chemicals that are sometimes present in transformer fluids), and evidence concerning the ‘Yusho” incident in Japan and the ‘Yu Cheng” incident in Taiwan in which many individuals suffered adverse effects after consuming rice oil contaminated with PCBs and furans. Bruce Hanes, who represented the nine remaining plaintiffs (the “Hanes plaintiffs”), designated Dr. G. John DiGregorio, M.D. to testify that PCBs had caused their injuries, and Arnold Schecter, M.D., M.P.H., to testify that their fear of future illness was reasonable. In a joint pretrial memorandum filed on July 17, 1992, the Kohn/Klehr and Hanes plaintiffs designated three additional trial experts — Deborah Barsotti, Ph.D., Benjamin Calesnick, M.D., and Arthur Zahalsky, Ph. D. — who had offered opinions for the plaintiffs in 1988. They also listed William J. Nicholson, Ph.D. and Cate Jenkins, Ph.D. as fact witnesses. Defendants moved to exclude these witnesses because plaintiffs had failed to designate them as experts in March, as the district court’s pre-trial order had required. The district court held five days of in limine hearings between July 28 and August 7,1992. Drs. Kopstein, Nisbet, and Sherman testified for the plaintiffs. Ten physicians and scientists testified for the defense. On October 21, 1992, the, court entered orders excluding all but one of plaintiffs’ experts (Dr. Kopstein). The court also excluded evidence concerning animal studies, dioxins and furans, and the incidents at Yusho and Yu Cheng. The court then granted summary judgment against the plaintiffs on their personal injury claims. The court explained that under our holding in Paoli I, the plaintiffs had to establish the following elements to make out a prima facie case: (1) that the defendants had released PCBs into the environment; (2) that the plaintiffs had somehow ingested those PCBs into their bodies; (3) that the plaintiffs have an injury; and (4) that PCBs are the cause of their .injury. See Paoli I, 916 F.2d at 860. Not surprisingly, after excluding plaintiffs’ experts, the court found that plaintiffs had no evidence on either exposure or causation and thus could not prove elements 2, 3, and 4. For similar reasons, the court granted summary judgment against the plaintiffs on their medical monitoring claims. Nine plaintiffs — Mabel Brown, K. Louise Jones, James Lament, Christopher Brown, Margherita Barbetta, Mary Retta Johnson, John Ingram, William Butler, arid Matthew Cunningham — also brought property damage claims against the defendants. The district court granted summary judgment in favor of the defendants on these claims as well. The court held that Pennsylvania law only allows recovery for diminution of a property’s market value if there has been permanent damage to the property; and the court found that plaintiffs could not prove such permanent damage in light of EPA’s proposed cleanup plan. The plaintiffs challenge the district court’s subject matter jurisdiction, all of its admissibility decisions, its legal conclusions regarding diminution of a property’s market value, and the court’s grant of summary judgment. We will affirm most of the district court’s decisions. We will reverse only its grant of summary judgment on a number of the present injury claims of Bessie Cunningham and Amber Burrell, and its grant of summary judgment on the plaintiffs’ claims for medical monitoring and diminution in property value. III. SUBJECT MATTER JURISDICTION OF THE DISTRICT COURT Plaintiffs’ original claims in 1986 included a CERCLA claim, 42 U.S.C. § 9601 et seq., which conferred federal question jurisdiction, 28 U.S.C. § 1331, on the district court. The court possessed pendent jurisdic-. tion over plaintiffs’ other claims. However, plaintiffs voluntarily dismissed the CERCLA claim after our ruling in Paoli I. Plaintiffs contend that, after this dismissal, the district court no longer had subject matter jurisdiction over the case because, absent the CERCLA claim, there was no federal question jurisdiction; nor was there complete diversity. In United Mine Workers v. Gibbs, 383 U.S. 715, 86 S.Ct. 1130, 16 L.Ed.2d 218 (1966), the Supreme Court held that in evaluating whether to exercise pendent jurisdiction, a district court must weigh “considerations of judicial economy, convenience and fairness to [the] litigants.” 383 U.S. at 726, 86 S.Ct. at U39. In holding that these factors favored retention of jurisdiction here, the district court acted within the ambit of its discretion. Considerations of judicial economy clearly weighed in favor of the district court retaining jurisdiction. Although considerations of judicial economy alone are generally insufficient to justify a district court’s decision to retain jurisdiction, see Shaffer v. Board of Sch. Directors, 730 F.2d 910, 912 (3d Cir.1984); Lovell Mfg. v. Export-Import Bank of U.S., 843 F.2d 725, 734-35 (3d Cir.1988), we have held such concerns sufficient when they are especially strong. In Lentino v. Fringe Employee Plans, Inc., 611 F.2d 474, 480 (3d Cir.1979), we upheld a district court’s decision to retain jurisdiction over a state law claim when plaintiffs dropped their federal claims on the morning of trial after there had already been a year of pretrial proceedings. The concerns of judicial economy here are at least as strong as they were in Lentino. Although the plaintiffs dropped their CERC-LA claim much earlier than the morning before trial, far more energy had been invested in the proceedings here than in Lenti-no. Six years of federal proceedings had occurred before the plaintiffs dropped their CÉRCLA claim, including extensive discovery. Moreover, the concern over judicial economy was combined here with two other factors strongly militating in favor of retention of jurisdiction. First, the district court would have continued to have jurisdiction over plaintiffs’ claims against Amtrak, see 28 U.S.C. § 1349 (providing district court jurisdiction over all corporations incorporated by an act of Congress in which the United States owns more than half the stock) even if it had dismissed most of plaintiffs’ claims for lack of jurisdiction. Amtrak doubtless would then have impleaded the other defendants, all of whom had deep pockets, thus changing the alignment of the parties but not the nature of the litigation. In such circumstances, a district court acts within its discretion in retaining jurisdiction. See, e.g., New Jersey Dept. of Env. Prot. v. Gloucester Env. Mgmt. Services, Inc., 719 F.Supp. 325, 337 (D.N.J.1989) (retaining jurisdiction in order to prevent “a litigation merry-go-round”). Second, plaintiffs were the ones who initially filed their claims in federal court and obtained a 1986 ruling that the CERCLA claims created federal jurisdiction. Plaintiffs dismissed their CERCLA claims and argued against federal jurisdiction only after the district court had first granted summary judgment against them. Thus, plaintiffs’ dismissal of their CERCLA claims may well constitute an attempt to forum shop by divesting the district court of jurisdiction. In Carnegie-Mellon Univ. v. Cohill, 484 U.S. 343, 108 S.Ct. 614, 98 L.Ed.2d 720 (1988), the Supreme Court held that the possibility of forum shopping is one factor a district court should take into account in exercising its discretion with respect to pendent jurisdiction. See id. at 351, 356, 357 & n. 12, 108 S.Ct. at 619, 622-23 & n. 12. Cohill, to be sure, was not about whether a district court should retain jurisdiction, but rather about what a district court should do after deciding not to retain jurisdiction, i.e. whether the court should dismiss the case, which might end it due to statute of limitations problems in state courts, or whether the court should remand the case to the state court from whence it had been removed. But Cohill did hold that one factor the district court should consider in deciding whether to remand the case to state courts is whether plaintiffs are attempting to forum shop. We hold that the same principle applies when the district court decides whether to retain jurisdiction in the first place. In sum, fairness to defendants along with judicial economy and convenience justify the district court’s decision to retain jurisdiction here. IV. WAS THE IN LIMINE HEARING TAINTED BY UNFAIR PROCEDURES? Before addressing the central issues in the case (regarding the admissibility of the opinions of the plaintiffs’ experts under Rules 702, 703 and 403), we must dispose of some preliminary questions. The plaintiffs contend that the district court should not have relied on the testimony of the defendants’ experts in excluding the testimony of the plaintiffs’ experts, because the defendants failed to designate these experts in accord with the time schedule announced by the district court. We review for abuse of discretion, and find none with respect to this ruling. Plaintiffs also submit that the district court should not have relied on its scheduling order to exclude the testimony of some of plaintiffs’ proposed experts. We do not have to reach the merits of this contention, because plaintiffs did not point to the testimony of these experts in opposition to summary judgment. A. Inadequate Opportunity to Depose Defense Experts On June 4, 1991, the district court issued an order requiring defendants to “designate all trial expert witnesses” by April 17, 1992 and giving the parties “until June 17, 1992 to depose expert witnesses.” (emphasis added). On June 25, 1992, well after the deadline the district court had set for identification of experts, defendants submitted affidavits from a new set of experts. Defendants intended to have these experts testify at the August in limine hearing but not at trial. Because discovery was closed, plaintiffs were unable to depose them. Plaintiffs moved to prevent these experts from testifying. The district court never ruled on this motion, allowed the experts to testify at the in limine hearing, and relied on their testimony in excluding much of plaintiffs’ evidence. Plaintiffs contend that this was error. On a purely formal level, we disagree for, as defendants correctly assert, the district court’s June 1991 order setting deadlines for the identification of experts was only directed at trial witnesses and said nothing about witnesses who were to testify only at the in limine hearing. But that conclusion does not settle the question. By coincidence, plaintiffs’ more significant claim of error is encapsulated in a recent law review article by Professor Berger, who argues that “[e]ourts should not permit the defendant to obtain a hearing on a motion in limine by relying on affidavits from experts unless their identity and reports have been supplied to the plaintiff in the course of discovery and the plaintiff had an opportunity to depose [them].” Margaret A. Berger, Procedural Paradigms for Applying the Daubert Test, 78 Minn.L.Rev. 1345, 1372 (1994). The district court certainly had the power to provide that the experts who were to testify at the in limine hearing be subject to discovery. See Berger, supra, at 1372 n. 141. (“A court undoubtedly has power pursuant to Federal Rule of Civil Procedure 16 to require parties to provide each other with expert reports and an opportunity for the deposition of experts retained in connection with in limine motions.”). And we generally agree with Professor Berger that because under Daubert a judge at an in limine hearing must make findings of fact on the reliability of complicated scientific methodologies and this fact-finding can decide the case, it is important that each side have an opportunity to depose the other side’s experts in order to develop strong critiques and defenses of their expert’s methodologies. See Paoli I, 916 F.2d at 854 (“[T]he detailed factual record requirement, firmly entrenched in our jurisprudence, requires adequate process at the evidentiary stage, particularly when a summary judgment may flow from it.” (internal citations omitted)). Given the “liberal thrust” of the federal rules, see Daubert, — U.S. at -, 113 S.Ct. at 2794 (internal quotation omitted), it is particularly important that the side trying to defend the admissibility of evidence be given an adequate chance to do so. Moreover, fairness suggests that each side should have an equal opportunity to depose the other side’s experts. In this ease, however, where we had yet to articulate our specific concern with depositions prior to the ruling of the district court, we conclude that the district court did not abuse its discretion in allowing experts, who had provided affidavits, to testify at the in limine hearing without being deposed. Moreover, the defendants submitted the affidavits of their experts four weeks prior to the hearing, so that the plaintiffs had a significant opportunity to prepare for the testimony of defendants’ experts. They also had extensive leeway at the in limine hearing, where the conservation of the time of the jury was not implicated, to consult with their experts regarding any new arguments presented by defendants’ experts. Under these circumstances, whatever unfairness to the plaintiffs that resulted from their inability to depose defendants’ experts is not sufficient to warrant a reversal for depositions and a new in limine hearing. B. Exclusion of Opinion of Experts for Whom No. 26(b) (U) Statements Were Filed In the June 4, 1991, scheduling order setting deadlines for designation of defense experts discussed above, the district court required plaintiffs to designate on or before March 17, 1992, “all trial expert witnesses and provide defendants with the substance of their trial testimony and the basis of their opinions at the time of designation in accordance with Rule 26(b)(4).” On July 17, 1992, four months after the deadline for designating experts and two weeks before the scheduled trial date, the plaintiffs filed a joint pretrial memorandum in which they named three expert witnesses, Drs. Calesnick, Bar-sotti, and Zahalsky, who had not been identified in plaintiffs’ March 1992 Rule 26(b)(4) statements. Plaintiffs also named Drs. Nicholson and Jenkins as fact witnesses even though defendants argue that they have no connection with this case and are really expert witnesses. The district court excluded all of these witnesses on the basis that plaintiffs had not named them by March 17,1992. Plaintiffs assert that because Drs. Cales-niek, Barsotti, and Zahalsky provided opinions in 1988 before the first summary judgment decision, the plaintiffs had designated them as experts before March 17, 1992, as required by the district court’s scheduling order. Moreover, plaintiffs argue, even if they violated the pre-trial order, the district court abused its discretion in sanctioning them by excluding the witnesses under the factors we set forth in Meyers v. Pennypack Woods Home Ownership Ass’n, 559 F.2d 894 (3d Cir.1977). We do not reach the merits of the district court’s ruling. Plaintiffs did not rely on these witnesses to oppose summary judgment. In fact, the plaintiffs did not even list these witnesses as trial witnesses until July 17, nine days after they had filed their opposition to summary judgment. As a result, our consideration of whether the district court was correct to grant summary judgment does not depend on whether the district court properly excluded these witnesses. “Where a party opposing a motion for summary judgment has the burden of persuasion, and the moving party has identified sufficient facts of record to demonstrate that no genuine issue of material fact remains, the nonmoving party is obliged to identify those facts of record which would contradict the facts identified by the movant.” Childers v. Joseph, 842 F.2d 689 (3d Cir.1988). See also Celotex Corp. v. Catrett, 477 U.S. 317, 322, 106 S.Ct. 2548, 2552-53, 91 L.Ed.2d 265 (1986). If the plaintiffs wished to rely on the opinions of Drs. Cales-nick Barsotti, Zahalsky, Nicholson and Jenkins to oppose summary judgment, they were required to identify the relevant facets of this testimony in their opposition to summary judgment. Nonetheless, because we are reversing the grant of summary judgment with respect to some plaintiffs and some issues, whether these witnesses can testify at trial may still matter on remand. We could therefore decide whether the district court’s original decision excluding these witnesses was an abuse of discretion, the matter having been properly put before us. However, we decline to do so, preferring to allow the district court to reconsider its decision in light of the additional time that will be available to the defendants to depose the witnesses. In excluding the witnesses originally, the district court partly relied on the proximity of the trial date to the revelation by plaintiffs of their intent to call these experts. And proximity is indeed one important factor. When the plaintiffs named these experts in July of 1992, two weeks before trial, giving defendants a significant time to depose them would have required delaying a long scheduled trial in a complex case that had already gone on for years. But after remand, the district court will easily b'e able to give the defendants significant time to depose the plaintiffs. In sum, in light of the changed circumstances that will be present upon remand, we choose not to determine whether the district court’s original decision constituted an abuse of discretion. Y. LEGAL STANDARDS FOR THE ADMISSIBILITY OF EXPERT OPINION The district court excluded plaintiffs’ remaining experts under Rules 702, 703, and 403. While the district court, the plaintiffs, and the defendants basically agree on the legal standards to be applied in analyzing admissibility, they also have some significant differences which repeatedly surfaced throughout the disputes over the admissibility of particular testimony. Accordingly, before analyzing the admissibility of the testimony of particular experts, we will first provide an overview of the legal standards under which we will evaluate that admissibility. Such an overview is also important in light of the Supreme Court’s recent decision in Dau-bert, which, although it largely adopted the Rule 702 test we announced in Downing, works certain changes in our jurisprudence on the admissibility of expert opinions. A. Rule 702 Rule 702 provides that: 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. 1. Qualifications Rule 702 has two major requirements. The first is that a witness proffered to testify to specialized knowledge must be an expert. We have interpreted this requirement liberally. See Paoli I, 916 F.2d at 855. We have held that a broad range of knowledge, skills, and training qualify an expert as such. See id. at 855. In Paoli I we ruled that the district court had abused its discretion in excluding the opinions of Drs. Barsotti, Za-halsky, and Nisbet. We explained that exclusion was not the proper remedy “simply because the experts did not have the degree or training which the district court apparently thought would be most appropriate.” Id. at 856. Defendants submit that when this court held that Rule 702 mandates a policy of liberal admissibility, all that it was doing was eliminating any requirement that a candidate have specific formal qualifications such as a degree in a particular field. They assert that we were simply directing the trial court to focus on the “substance of a proffered expert’s background and its fit with respect to the issue at hand.” Thus, defendants suggest, when a trial court evaluates an expert’s substantive rather than formal qualifications, it does not have to use a liberal policy of admission. But this is incorrect. Rule 702’s liberal policy of admissibility extends to the substantive as well as the formal qualification of experts. We have eschewed imposing overly rigorous requirements of expertise and have been satisfied with more generalized qualifications. See Hammond v. International Harvester Co., 691 F.2d 646, 652-53 (3d Cir.1982) (holding that an engineer, whose only qualifications were sales experience in the field of automotive and agricultural equipment and teaching high school automobile repair, nevertheless could testify in a products liability action involving tractors); Knight v. Otis Elevator Co., 596 F.2d 84, 87-88 (3d Cir.1979) (holding that an expert could testify that unguarded elevator buttons constituted a design defect despite expert’s lack of specific background in design and manufacture of elevators). As we explain below, however, the level of expertise may affect the reliability of the expert’s opinion. 2. Reliability The second requirement of Rule 702 is that the expert must testify to “scientific, technical or other specialized knowledge [that] will assist the trier of fact.” Fed.R.Evid. 702. The Supreme Court recently evaluated the meaning of this requirement in Daubert and held that Rule 702 does not incorporate the common law Frye rule in which expert testimony is admissible only insofar as it is based on a technique generally accepted in the scientific community. Instead, the Supreme Court agreed with this Court’s basic holding in Downing that an expert’s testimony is admissible so long as the process or technique the expert used in formulating the opinion is reliable. See Daubert, — U.S. at -, 113 S.Ct. at 2794-95 (“That the Frye test was displaced by the Rules of Evidence does not mean, however, that the Rules themselves place no limits on the admissibility of purportedly scientific evidence. Nor is the trial judge disabled from screening such evidence. To the contrary, under the Rules the trial judge must ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable.”); Downing 753 F.2d at 1237. Daubert explains that the language of Rule 702 requiring the expert to testify to scientific knowledge means that the expert’s opinion must be based on the “methods and procedures of science” rather than on “subjective belief or unsupported speculation”; the expert must have “good grounds” for his or her belief. Daubert, — U.S. at-•, 113 S.Ct. at 2795. In sum, Daubert holds that an inquiry into the reliability of scientific evidence under Rule 702 requires a determination as to its scientific validity. Id. at-, 113 S.Ct. at 2795 n. 9. Daubert suggests several factors that a district court should take into account in evaluating whether a particular scientific methodology is reliable (i.e. scientifically valid), including the testability of the expert’s hypothesis (“whether it can be (and has been) tested”), Daubert, — U.S. at -, 113 S.Ct. at 2796, whether the methodology has been subjected to peer review and publication, the frequency by which the methodology leads to erroneous results, the existence and maintenance of standards controlling the technique’s operation, and whether the methodology has been generally accepted in the scientific community. See Daubert, — U.S. at-, 113 S.Ct. at 2796-97. We listed very similar factors a district court should consider in Downing. See Downing, 753 F.2d at 1238-39. Daubert lists two factors not listed in Downing — whether a method produces testable hypotheses and the existence of standards controlling the technique’s operation, and Daubert leaves off its list several factors listed in Downing — the degree to which the expert testifying is qualified, the relationship of a technique to “more established modes of scientific analysis,” and the “non-judicial uses to which the scientific technique are put.” Downing, 753 F.2d at 1238-39; see Daubert, — U.S. at- -, 113 S.Ct. at 2796-97. But Daubert specifically refuses to disavow any the particular factors we listed in Downing. See Dau-bert, — U.S.-, 113 S.Ct. at 2797 n. 12. And Daubert, like Downing, indicates that the inquiry as to whether a particular scientific technique or method is reliable is a flexible one. See id. at-, 113 S.Ct. at 2796, Downing, 753 F.2d at 1238-39. We now make clear that a district court should take into account all of the factors listed by either Daubert or Downing as well as any others that are relevant. 3. Fit In addition to reliability, Rule 702 requires that the expert’s testimony must assist the trier of fact. As we put it in Downing, admissibility depends in part on “the proffered connection between the scientific research or test result to be presented and particular disputed factual issues in the case.” Downing, 753 F.2d at 1237. See Daubert, — U.S.-, 113 S.Ct. at 2795-96 (explicitly adopting the “fit” requirement of Downing). For example, animal studies may be methodologically acceptable to show that chemical X increases the risk of cancer in animals, but they may not be methodologically acceptable to show that chemical X increases the risk of cancer in humans. Daubert explains that, “ ‘[flit’ is not always obvious, and scientific validity for one purpose is not necessarily scientific validity for other, unrelated purposes.” Id. at-, 113 S.Ct. at 2796. Thus, even if an expert’s proposed testimony constitutes scientific knowledge, his or her testimony will be excluded if it is not scientific knowledge for purposes of the case. “Rule 702’s ‘helpfulness’ standard requires a valid scientific connection to the pertinent inquiry as a precondition to admissibility.” Id. (emphasis added). For example, in order for animal studies to be admissible to prove causation in humans, there must be good grounds to extrapolate from animals to humans, just as the methodology of the studies must constitute good grounds to reach conclusions about the animals themselves. Thus, the requirement of reliability, or “good grounds,” extends to each step in an expert’s analysis all the way through the step that connects the work of the expert to the particular case. 4. The roles of judge and jury: how high a threshold for reliability? Plaintiffs’ basic position in their challenge to each of the district court’s admissibility decisions is that the district court improperly usurped the role of the jury by the manner in which it analyzed admissibility. Plaintiffs first argue that, so long as they have made a prima facie showing that an expert’s testimony is reliable, it is up to the jury to evaluate the expert’s testimony. They assert that for the judge to evaluate competing evidence on reliability before determining admissibility would force plaintiffs to prove their case twice — once to the judge in order to persuade him or her to admit the evidence and once to the jury to persuade it of liability. But plaintiffs’ position that a party who wants to introduce expert testimony must make only a prima facie showing that a technique is reliable (e.g., the testimony of a single qualified expert) is specifically foreclosed by precedent. Daubert holds that admissibility under Rule 702 is governed by Rule 104(a), which requires the judge to conduct preliminary factfinding, to make “a preliminary assessment of whether the reasoning or methodology underlying the testimony is scientifically valid,” and thus enables the judge to exclude evidence presented in plaintiffs’ prima facie case. Daubert, — U.S. at -, 113 S.Ct. at 2796. Similarly, we held in Downing that “it is plain that the proponent must make more than a prima facie showing .■.. that a technique is reliable.” Downing, 753 F.2d at 1240 n. 21. We added that, in contrast to the view that the admission of scientific testimony is a matter of conditional relevancy governed by Rule 104(b), “novel scientific evidence carries with it concerns over trustworthiness and reliability akin to those raised by offers of hearsay evidence. When there is a serious question of reliability of evidence, it is appropriate for the court to exercise to some degree an evidentiary screening function.” Id. Cf. In re Japanese Elec. Prod., 723 F.2d 238, 276-77 (3d Cir.1983) (implying that Rule 104(a) requires judges to make factual evaluations in making Rule 703 determinations). This does not megn that plaintiffs have to prove their ease 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. As the Supreme Court has explained in describing the effect of the preponderance standard of Rule 104(a) generally, “[t]he inquiry made by a court ... is not whether the proponent of the evidence wins or loses his case on the merits, but whether the evidentiary Rules have been satisfied.” Bourjaily v. United States, 483 U.S. 171, 175, 107 S.Ct. 2775, 2778, 97 L.Ed.2d 144 (1987). 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 Dau-bert indicates, “[t]he focus ... must be solely on principles and methodology, not on the conclusions that they generate.” Daubert, — U.S. at -, 113 S.Ct. at 2797. The grounds for the expert’s opinion merely have to be good, they do not have to be perfect. The judge might think that there are good grounds for an expert’s conclusion even if the judge thinks that there are better grounds for some alternative conclusion, and even if the judge thinks that a scientist’s methodology has some flaws such that if they had been corrected, the scientist would have reached a different result. As we explained in Paoli I, “the reliability requirement must not be used as a tool by which the court excludes all questionably reliable evidence.” Paoli I, 916 F.2d at 857. The “ultimate touchstone is helpfulness to the trier of fact, and with regard to reliability, helpfulness turns on whether the expert’s ‘technique or principle [is] sufficiently reliable so that it will aid the jury in reaching accurate results.’ ” DeLuca, 911 F.2d at 956 (quoting 3 J. Weinstein & M. Berger, Weinstein’s Evidence 702[03], at 702-35 (1988)). A judge frequently should find an expert’s methodology helpful even when the judge thinks that the expert’s technique has flaws sufficient to render the conclusions inaccurate. He or she will often still believe that hearing the expert’s testimony and assessing its flaws was an important part of assessing what conclusion was correct and may certainly still believe that a jury attempting to reach an accurate result should consider the evidence. See Paoli I, 916 F.2d at 857 (helpfulness requires more than bare logical relevance, but there is a strong preference for admission) (citing Downing, 753 F.2d at 1235). The same standard of reliability extends to the step in the expert’s analysis that “fits” his or her conclusions to the case at hand. Once again, we emphasize that the standard is not that high. For example, in Paoli I, we held that testimony that PCBs cause liver cancer “fit” the case even in the absence of plaintiffs who had liver cancer, because an expert’s affidavit suggested that increased risk of liver cancer was probative of increased risk of other forms of cancer. See Paoli I, 916 F.2d at 858. Nonetheless, the standard is higher than bare relevance. In addition to arguing that the district court usurped the role of the jury by requiring more than a prima facie showing of reliability, plaintiffs submit that the district court mistakenly applied the reliability inquiry to expert testimony that should not have been subject to that inquiry. Both Daubert and Downing require that expert testimony be based on the methods and procedures, the processes and techniques of science. In Pao-li I we suggested that so long as any deviation the expert made from a rehable method merely constituted a change in the application of that method, the expert’s testimony remained based on a rehable scientific method. We though that ferreting out misapplication fell within the province of the jury, and that only if the expert so altered a rehable methodology as to skew it would the rehabihty inquiry of Downing be apphcable to the altered methodology. See Paoli I, 916 F.2d at 858. Plaintiffs assert that the district court apphed the Downing inquiry to methodologies that merely constituted shght alterations of rehable methodologies. However, after Daubert, we no longer think that the distinction between a methodology and its apphcation is viable. To begin with, it is extremely elusive to attempt to ascertain which of an expert’s steps constitute parts of a “basic” methodology and which constitute changes from that methodology. If a laboratory consistently fails to use certain quality controls so that its results are rendered unreliable, attempting to ascertain whether the lack of quahty controls constitutes a failure of methodology or a failure of apphcation of methodology may be an exercise in metaphysics. Moreover, any misapplication of a methodology that is significant enough to render it unreliable is likely to also be significant enough to skew the methodology. As suggested, Daubert inters any need for us to make such a distinction, for Daubert’s requirement that the expert testify to scientific knowledge—conclusions supported by good grounds for each step in the analysis— means that any step that renders the analysis unrehable under the Daubert factors renders the expert’s testimony inadmissible. This is true whether the step completely changes a reliable methodology or merely misapplies that methodology. Finally, plaintiffs contend that the district court usurped the role of the jury by making admissibility decisions based on its disagreement with the conclusions of plaintiffs’ experts. Plaintiffs are correct, of course, that Daubert requires the judge’s admissibility decision to focus not on the expert’s conclusions but on his or her principles and methodology. See Daubert, — U.S. at-, 113 S.Ct. at 2797. But we think that this distinction has only limited practical import. When a judge disagrees with the conclusions of an expert, it will generally be because he or she thinks that there is a mistake at some step in the investigative or reasoning process of that expert. If the judge thinks that the conclusions of some other expert are correct, it will likely be because the judge thinks that the methodology and reasoning process of the other expert are superior to those of the first expert. This is especially true given that the expert’s view that a particular conclusion “fits” a particular case must itself constitute scientific knowledge — a challenge to “fit” is very close to a challenge to the expert’s ultimate conclusion about the particular case, and yet it is part of the judge’s admissibility calculus under Daubert, Thus, as we explained above, we think that the primary limitation on the judge’s admissibility determinations is that the judge should not exclude evidence simply because he or she thinks that there is a flaw in the expert’s investigative process which renders the expert’s conclusions incorrect. The judge should only exclude the evidence if the flaw is large enough that the expert lacks “good grounds” for his or her conclusions. 5. Confusion — Rule 403 In Downing we explained that under Rule 702, admissibility of scientific testimony turns not only on reliability but also on the possibility that admitting the evidence would overwhelm, confuse, or mislead the jury. See Downing, 753 F.2d at 1240. We held that in conducting this balancing inquiry, there is a presumption of helpfulness. See id. at 1241 (citing Japanese Elec. 723 F.2d at 279). The extent to which an adverse party has had notice and the opportunity to present his or her own experts is also relevant. Moreover, a district court cannot exclude a scientific technique as too confusing and overwhelming simply based on its conclusion that scientific techniques by their very nature confuse and overwhelm the jury. There must be something about the particular scientific technique such as its posture of mythic infallibility that makes it especially overwhelming. See id. at 1239 (overturning the district court’s exclusion of Dr. Nicholson’s meta-analysis because its conclusion that his testimony was overwhelming was based merely on its scientific nature and his credentials). We explained in Downing that Rule 702 analysis partly incorporates Rule 403 analysis but leaves some room for Rule 403 to operate independently. See Downing, 753 F.2d at 1242. For example, we noted that a judge might use Rule 403 to exclude an expert’s critique of eyewitness testimony even though the critique met the requirements of Rule 702 if there was evidence of defendant’s guilt other than eyewitness testimony which would make efforts to criticize eyewitness testimony a waste of time. In Daubert, the Supreme Court seems to have inverted our view that much of Rule 403 analysis conflates into Rule 702; rather the Court seems to have conflated the confusion/overwhelming impact prong of our Rule 702 analysis into its Rule 403 analysis. The Daubert Court did not mention the confusion/overwhelming prong when discussing Rule 702 but did provide support for application of essentially similar analysis under the rubric of Rule 403. The Court noted that Rule 403’s balancing test of the probative against the prejudicial value of evidence has a special role in cases involving expert witnesses. It stated that because expert evidence is often more misleading than other evidence, Rule 403 gives a judge more power over experts than over lay witnesses. See Daubert, — U.S. at-, 113 S.Ct. at 2798. This, however, does not change our opinion that in order for a district court to exclude scientific evidence, there must be something particularly confusing about the scientific evidence at issue — something other than the general complexity of scientific evidence. 6. Procedural concerns regarding the Rule 403/702 balancing test In Paoli I we held that Rule 403 is rarely appropriate as a basis of pre-trial exclusion, because a judge cannot ascertain potential relevance -until that judge has a virtual surrogate for a trial record. See Paoli I, 916 F.2d at 859-60. There, many of the district court’s admissibility determinations were based in part on Rule 403; thus, it is important to determine whether the in limine hearing in the district court created the “virtual surrogate for a trial record” that we have required before exclusion is permissible. Plaintiffs argue that the in limine hearing did not create such a record because they did not have an opportunity to depose defendant’s experts ahead of time. As compared with a trial, plaintiffs assert, this made it much more difficult to impeach defendants’ experts and to bolster the claims of their own experts. We think that the in limine hearing conducted here was more than adequate as a basis for a Rule 403 determination — to hold otherwise given the extensive proceedings in the district court would be to require not a “virtual surrogate for a trial record” but a trial itself. B. Rule 703 While Rule 702 focuses on an expert’s methodology, Rule 703 focuses on the data underlying the expert’s opinion. Under Rule 703: The facts or data in the particular case upon which an expert bases an opinion or inference may be those perceived by or made known to the expert at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence. Under our case law on Rule 703, “the proper inquiry is not what the court deems reliable, but what experts in the relevant discipline deem it t