Full opinion text
OPINION SCHROEDER, Chief Circuit Judge: 7. Introduction. The origins of this case trace back more than sixty years to the height of World War II when the federal government solicited Appellants E.I. DuPont de Nemours & Co., General Electric, Inc., UNC Nuclear Industries, Inc., Atlantic Richfield Co., and Rockwell International Corp., (collectively “Defendants”) to operate the Han-ford Nuclear Weapons Reservation (“Han-ford”) in southeastern Washington. The Hanford Reservation was a plutonium-production facility that helped make the atomic bomb that dropped on Nagasaki, Japan in World War II. A regrettable Hanford byproduct was the radioiodine emitted into the surrounding area. The plaintiffs in this litigation are over two thousand residents who now claim that these emissions, known as I-131, caused various cancers and other life-threatening diseases. The first group of plaintiffs filed a complaint in 1990 under the federal statute governing nuclear accidents, the Price-Anderson Act (“PAA”), claiming they were entitled to damages for injuries arising from a nuclear incident pursuant to 42 U.S.C. § 2210. The history is discussed in our earlier opinions in In re Hanford Nuclear Reservation Litigation, 292 F.3d 1124 (9th Cir.2002) (“In re Hanford ”); and Berg v. E.I. DuPont De Nemours & Co., 293 F.3d 1127 (9th Cir.2002) (“Berg ”). After almost two decades of litigation, which already has included two appeals to this court, the parties in 2005 agreed to a bellwether trial. The trial was designed to produce a verdict that would highlight the strengths and weaknesses of the parties’ respective cases and thus focused on six plaintiffs (“Plaintiffs”) who were representative of the larger group. The purpose of the trial was to promote settlement and bring long-overdue resolution to this litigation. Before us on appeal is a litany of issues stemming from the bellwether trial. A threshold issue is whether Defendants may seek complete immunity under the common law government contractor defense, because they were operating Hanford at the request of the federal government. We hold that the defense is inapplicable as a matter of law, because Congress enacted the PAA before the courts recognized the government contractor defense, and the PAA provides a comprehensive liability scheme that precludes Defendants’ reliance on such a defense. In the alternative, Defendants argue that even if they are not immune, they are not strictly liable for any 1-131 emissions, because the amounts of the emissions were within federally-authorized levels; the plutonium-production process was not an abnormally dangerous activity that would create strict liability; and even if it were, Defendants qualify for the “public duty” exception to strict liability. The district court held that none of Defendants’ contentions were sufficient to relieve them of strict liability for the injuries they caused. We agree. With respect to the trial itself, the district court with admirable diligence ruled on many issues of first impression. We hold that under Washington law, the district court properly instructed the jury that to impose liability, it had to find Han-ford was the “but for” cause of Plaintiffs’ diseases and not just a contributing cause under the more lenient “substantial factor” test. The court also made a host of evi-dentiary rulings that are before us on appeal. We hold that three of these rulings constitute reversible error with respect to three of the Bellwether Plaintiffs. There are statute of limitations issues as well. We hold that any Hanford Plaintiffs who filed independent suits pending class certification lost the benefits of class action tolling, thus potentially rendering their suits untimely. Because the record before us is incomplete as to the date necessary to measure the appropriate tolling period for various plaintiffs, we remand the statute of limitations issues to the district court for further proceedings. Lastly, we hold that the district court properly dismissed any medical monitoring claims as not cognizable under the PAA. This is consistent with our decision in Berg, 293 F.3d 1127. II. Background. The United States government constructed Hanford during World War II to manufacture plutonium for military purposes. The facility was a component of the Army Corps of Engineer’s secret Manhattan Project, with the primary objective of developing an atomic bomb. In 1942, the Army Corps began hiring civilian contractors to help build and operate the Han-ford facility. It first recruited the University of Chicago Metallurgical Laboratory (“Met Lab”) to design the process and equipment to produce plutonium. It then solicited E.I. DuPont de Nemours & Co. (“DuPont”) to actually run the facility. It is apparent the government itself did not have the expertise or resources to operate Hanford. DuPont initially refused. The government, however, persisted and implored DuPont to run the plutonium-production facility, because, as the government provided in DuPont’s contract, the project was of the “utmost importance” and was “necessary in facilitating the prosecution of the war.” DuPont eventually acquiesced, stating it would run the facility out of patriotic considerations. It accepted only one dollar as payment for its services. Several years later, the Hanford facility successfully produced the plutonium that was used in 1945 to drop the atomic bomb on Nagasaki and effectively end World War II.(The bomb dropped on Hiroshima was uranium-based, not plutonium-based). As part of the plutonium-production process, the Hanford facility emitted 1-131, a fission byproduct known as radioiodine. 1-131 was known at the time to have potential adverse health effects on humans. Accordingly, the Met Lab scientists set tolerance doses for human exposure. For example, the Met Lab determined that the human thyroid should not absorb more than one rad per day for those individuals subject to continuous exposure in the area. A rad is a measurement of the amount of radioiodine absorbed into an organ or tissue. On the basis of these safe exposure limit estimates, the Met Lab approved a detailed operating procedure that would ensure that the plutonium was produced within those emission limits. The key to decreasing 1-131 emissions was to allow for longer cooling times of the uranium slugs used to produce the plutonium. This strategy, however, often conflicted with the federal government’s orders to increase plutonium production. On September 1, 1946, DuPont transferred its duties to General Electric (“GE”),' which also agreed to earn no profit from its work. GE ran the Hanford facility through the Cold War. During the period of its operation, GE asked the federal government to increase cooling times to allow for lower emissions of 1-131. By this time, Congress had established the Atomic Energy Commission (“AEC”), see 42 U.S.C. §§ 2011-2013 (1946), and GE was bound by its determinations. The AEC denied the request for longer cooling times, and GE continued to produce plutonium consistent with government demands. By the 1950s, however, significant improvements were made to the production process, and 1-131 emission levels dropped. In 1987, the United States Department of Energy (“DOE”) created the Hanford Environmental Dose Reconstruction Project (“HEDR”), overseen by the Center for Disease Control and Prevention. The underlying purpose of the HEDR was to estimate and reconstruct all radionuclide emissions from Hanford from 1944 to 1972 in order to ascertain whether neighboring individuals and animals had been exposed to harmful doses of radiation. Of particular concern to the HEDR were the estimated doses of 1-131 received by the thyroid glands of humans, principally through consumption of milk from cows that ingested contaminated vegetation on neighboring farms and pastures. The HEDR concluded that 1-131 emissions peaked during the period from 1944 to 1946, when an estimated 88% of Hanford’s total iodine emissions occurred. HEDR explained that in later years, emissions declined because of technological advances. In 1990, the Technical Steering Panel of HEDR released a report entitled Initial Hanford Radiation Dose Estimates that publicly disclosed for the first time that large quantities of radioactive and non-radioactive substances had been released from Han-ford, beginning in the 1940s. This disclosure sparked a blaze of litigation. Thousands of plaintiffs filed suit pursuant to the Price-Anderson Act, 42 U.S.C. § 2210(n)(2), which had been amended in 1988 to provide exclusive federal jurisdiction over all claims arising from a nuclear incident, otherwise known as public liability actions. The PAN allowed the plaintiffs to sue private parties, such as DuPont, and to consolidate the claims in federal district court. Id. While Congress wanted to ensure that victims of nuclear incidents recovered compensation, it also included government indemnification provisions in the PAA to give private parties an incentive to participate in the nuclear industry. See, e.g., S. Rep. No. 100-70, at 14 (1988), reprinted in 1988 U.S.C.C.A.N. 1424, 1425-26. The PAA provides that although federal courts have exclusive and original jurisdiction over claims stemming from nuclear incidents, the substantive rules of decision are provided by the law of the state in which the nuclear incident occurs. See 42 U.S.C. § 2014(hh). Plaintiffs therefore brought tort claims under Washington law, asserting that because Defendants were engaged in an abnormally dangerous activity, they were strictly liable for any Han-ford-caused radiation illness. On August 6, 1990, a group of plaintiffs filed a joint consolidated complaint in the Eastern District of Washington, alleging a class action against Defendants. In 1991, the district court consolidated any and all Hanford-related actions pending in various courts, directed preparation of one consolidated complaint, and designated specific lead counsel for all parties. In an order dated September 22, 1994, the district court addressed the issue of class certification and decided to reserve decision under Federal Rule of Civil Procedure 23(b)(3) pending further discovery on causation issues. Accordingly, pending class certification, the litigation proceeded as a consolidated action. Throughout this period, the district court entertained a handful of disposi-tive motions, which led to two appeals to this court. In 2002, we heard In re Hanford, 292 F.3d 1124, challenging the district court’s dismissal of plaintiffs who could not establish they received a “doubling dose” of radiation. We held that Plaintiffs’ claims should proceed even if they could not show that Hanford radiation doubled their risk of illness, and we remanded for trial. Id. at 1139. We also heard the appeal in the related case, Berg, 293 F.3d 1127. The Berg plaintiffs had not yet suffered from any illness, but sued Defendants for medical monitoring. We held that medical monitoring claims were not compensable under the PAA and upheld the district court’s dismissal of those actions with prejudice. Id. at 1133. After our decisions in In re Hanford and Berg, Judge William Fremming Nielsen steered the case toward resolution. The parties agreed to proceed with a bellwether trial, hoping it would reveal the strengths and weaknesses of their respective cases and thus pave the way for a settlement. The parties eventually agreed on twelve bellwether plaintiffs. Six of these plaintiffs had their claims dismissed on dispositive, pre-trial motions. The remaining six plaintiffs went to trial in April 2005. The Bellwether Plaintiffs represent plaintiffs who suffer from various thyroid diseases they claim were caused by radiation emanating from Hanford. Plaintiffs Gloria Wise and Steven Stanton have thyroid cancer. Plaintiffs Wanda Buckner, Shirley Carlisle, and Kathryn Goldbloom suffer from hypothyroidism, a condition that slows the body’s metabolism. Hypothyroidism is most frequently caused by Hashimoto’s disease, an illness that Plaintiffs claim was caused by Hanford radiation. Plaintiff Shannon Rhodes suffers from lung cancer, which her doctors concluded was a form of Hurthle cell thyroid cancer that had metastasized from a thyroid lobe previously removed. Prior to trial, the Bellwether Plaintiffs made several motions to strike Defendants’ affirmative defenses. Defendants first claimed that the government contractor defense insulated them from all liability. The district court, in an unpublished 2003 order, struck the defense under Federal Rule of Civil Procedure 12(b), holding that the PAA displaced any such defense as a matter of law. In a published order, the court also ruled that plutonium production at Hanford was an abnormally dangerous activity warranting, strict liability under Washington law. In re Hanford Nuclear Res. Litig., 350 F.Supp.2d 871, 888 (E.D.Wash.2004). It then limited the issues at trial to causation and damages. Id. The primary dispute at trial was whether the amount of radiation to which each plaintiff was exposed was sufficient to be the cause-in-fact of his or her thyroid disease. There was extensive testimony that 1-131 radiation causes Hashimoto’s disease, a cause of hypothyroidism, and that 1-131 can also be a contributing factor to thyroid cancer. The testimony revealed, however, that to date epidemiological studies can establish only that radiation of at least 100 rads is a contributing factor to thyroid illness. Some epidemiological studies hypothesize that 40 rads might cause Hashimoto’s disease, but there are no data beyond that threshold. Because many Plaintiffs were not exposed to radiation above 40 rads, and no Plaintiff was exposed to radiation above 100 rads, Plaintiffs had to present expert testimony that scientific extrapolation permitted a finding of causation below 40 rads. Their primary experts were Dr. Terry Davies, an endocrinologist, .Dr. Sara Peters, a pathologist, Dr. F. Owen Hoffman, a causation expert, and Dr. Colin Hill, a radiation cell biologist. Plaintiffs also proffered the expert testimony of epidemiologist Dr. A. James Ruttenber, but key parts of his testimony relating to causation were excluded. After fourteen days of trial and four days of deliberations, the jury found in favor of two plaintiffs, Steve Stanton and Gloria Wise; the jury hung with respect to one plaintiff, Shannon Rhodes; and it found in favor of Defendants with respect to the remaining three plaintiffs, Wanda Buckner, Shirley Carlisle, and Kathryn Goldbloom. As damages for prevailing plaintiffs, the jury awarded Stanton $227,508 and Wise $317,251. Because the jury could not reach a verdict with respect to Plaintiff Rhodes, the district court declared a mistrial. Rhodes retried her claims in front of a second jury in November 2005, and the jury entered a defense verdict on all counts. Rhodes, along with the three non-prevailing plaintiffs in the first trial, appeal a variety of evidentiary rulings, as well as the district court’s jury instruction that under Washington law Plaintiffs had to prove “but-for” causation, rather than “substantial factor” causation. Defendants appeal the judgments entered in favor of the two prevailing plaintiffs, claiming the district court erred as a matter of law in striking the government contractor defense. In the alternative, Defendants argue that Plaintiffs may not proceed under a strict liability theory, because the 1-131 emissions were within federally-authorized levels. They also contend the plutonium-production process was not an abnormally dangerous activity under Washington law and, even if it were, that Defendants qualify for the narrow “public duty” exception to strict liability. Defendants also contend that prevailing Plaintiff Wise’s suit was untimely under Washington’s statute of limitations. See Am. Pipe & Constr. Co. v. Utah, 414 U.S. 538, 94 S.Ct. 756, 38 L.Ed.2d 713 (1974). Wise had filed an independent action in 1997, likely beyond the statutory period, but Defendants did not invoke American Pipe and the district court allowed Wise’s claim to proceed as part of the pending class action. Apart from the issues relating to the Bellwether Plaintiffs, Plaintiffs Pamela Durfey, Paulene Echo Hawk, and Dorothy George, who do not yet have symptoms of any thyroid disease, sued Defendants for the costs of medical monitoring. The district court, following this court’s decision in Berg, 293 F.3d at 1132-33, held that the PAA precluded any medical monitoring claims that were unaccompanied by physical injury. Rather than remanding those claims to state court, however, the district court held that the PAA bestowed exclusive jurisdiction in the federal courts for claims arising from a nuclear incident, and that therefore the PAA’s provisions preempted any state-derived medical monitoring claim. Accordingly, it directed entry of final judgment for DuPont under Federal Rule of Civil Procedure 54(b). The plaintiffs appeal this dismissal. III. The Government Contractor Defense. The overarching issue before us is Defendants’ contention that the government contractor defense is available to them as a matter of law and that it provides complete immunity from liability if its substantive requirements are satisfied. The district court held that the affirmative defense was inapplicable as a matter of law because the provisions of the PAA cannot be reconciled with the defense and implicitly displace it. We review de novo the district court’s conclusion that the affirmative defense is unavailable, United States v. Griffin, 440 F.3d 1138, 1143 (9th Cir.2006), and we reach the same conclusion. The government contractor defense is by now an established component of federal common law, but it was first recognized by the Supreme Court less than twenty years ago in Boyle v. United Techs. Corp., 487 U.S. 500, 108 S.Ct. 2510, 101 L.Ed.2d 442 (1988). The defense is intended to implement and protect the discretionary function exception of the Federal Tort Claims Act (“FTCA”), 28 U.S.C. § 2680(a), which was enacted after World War II. The defense allows a contractor-defendant to receive the benefits of sovereign immunity when a contractor complies with the specifications of a federal government contract. Boyle, 487 U.S. at 511-12, 108 S.Ct. 2510. As the Court said in Boyle, “[i]t makes little sense to insulate the Government against financial liability for the judgment that ... equipment is necessary when the Government produces the equipment itself, but not when it contracts for the production.” Id. at 512, 108 S.Ct. 2510. As a threshold matter, we agree with Defendants that the government contractor defense applies not only to claims challenging the physical design of a military product, but also to the process by which such equipment is produced. Accordingly, a contractor who agrees to operate a production facility pursuant to government specifications may qualify for the defense. The issue here, however, is whether the PAA preempts reliance on the common law doctrine, either because the defense contradicts the federal statute or because the statute predates the defense. Congress is presumed to “legislate against a background of common-law adjudicatory principles.” Astoria Fed. Sav. & Loan Ass’n v. Solimino, 501 U.S. 104, 108, 111 S.Ct. 2166, 115 L.Ed.2d 96 (1991). A federal statute enacted after a common law doctrine has been established will not therefore abrogate the federal common law rule unless the statute speaks directly to the question addressed by common law. United States v. Texas, 507 U.S. 529, 534, 113 S.Ct. 1631, 123 L.Ed.2d 245 (1993). This is because “where a common-law principle is well established ... the courts may take it as given that Congress has legislated with an expectation that the principle will apply except when a statutory purpose to the contrary is evident.” Astoria, 501 U.S. at 108, 111 S.Ct. 2166(internal quotations and citations omitted) (holding that the court should assume Congress drafted the Age Discrimination in Employment Act with the common law administrative estoppel doctrine in mind); see also Pasquantino v. United States, 544 U.S. 349, 359, 125 S.Ct. 1766, 161 L.Ed.2d 619 (2005). Whether the PAA preempts the government contractor defense is therefore a two-step inquiry. We must first determine whether the government contractor defense was well-established at the time Congress enacted the operative version of the PAA. If so, we must determine whether a statutory purpose contrary to the government contractor defense is evident. The defense fails the first inquiry. Defendants are not entitled to the government contractor defense, because the statute predates clear judicial recognition of any such defense. In addition, the statute’s comprehensive liability scheme is patently inconsistent with the defense and precludes its operation in this case. The Supreme Court’s decision in Boyle was filed on June 27, 1988. Less than two months later, the PAA was amended, on August 20, 1988, to include the pertinent language establishing exclusive federal jurisdiction for all public liability claims arising from nuclear incidents. While the government contractor defense was technically a recognized common law principle at the time Congress enacted the PAA, it was hardly a well-established doctrine. See Astoria, 501 U.S. at 108, 111 S.Ct. 2166.(noting that courts should presume Congress legislated with an expectation that a common law doctrine would apply only if the common-law principle was well-established). When drafting the bill, Congress could not have considered whether or not the government contractor defense would affect liability under the PAA, because the Supreme Court defined the defense only a few weeks before the PAA was signed into law. The origins of the defense in the cases antecedent to Boyle do not materially affect this analysis. In 1940, the Supreme Court arguably planted the seeds of the government contractor defense in Yearsley v. W.A. Ross Constr. Co., 309 U.S. 18, 20-21, 60 S.Ct. 413, 84 L.Ed. 554 (1940). It held that an agent of the government could not be held liable under the Takings Clause for the defective construction of a dam that damaged land, as long as the agent followed government specifications for the dam’s construction. The Court limited the applicability of the defense to principal-agent relationships where the agent had no discretion in the design process and completely followed government specifications. Nothing in Yearsley extended immunity to military contractors exercising a discretionary governmental function. See Boyle, 487 U.S. at 524-25, 108 S.Ct. 2510(J. Brennan, dissenting) (Yearsley is “a slender reed on which to base so drastic a departure from precedent” .... “[It] has never been read to immunize the discretionary acts of those who perform service contracts for the Government”). While some circuit courts began extending the Yearsley doctrine to military contractors as early as the 1960s, see McKay v. Rockwell Int’l Corp., 704 F.2d 444, 448-49 (9th Cir.1983) (citing cases), other circuits held that Yearsley was clearly limited to principal-agent relationships and did not apply to military contractors, see, e.g., Bynum v. FMC Corp., 770 F.2d 556, 564 (5th Cir.1985). In light of the conflicting authority on the matter, it is clear that neither the scope nor the contours of the defense were well-defined until the Supreme Court’s 1988 decision in Boyle. We therefore conclude that the government contractor defense was not well-established at the time Congress enacted the PAA. Because Congress did not enact the PAA against a back-drop of common law principles that included the government contractor defense, we cannot grant immunity from liability. Astoria, 501 U.S. at 108, 111 S.Ct. 2166. The federal common law defense exists only in the absence of explicit statutory directive. Milwaukee v. Illinois, 451 U.S. 304, 312-13, 101 S.Ct. 1784, 68 L.Ed.2d 114 (1981); Boyle, 487 U.S. at 504, 108 S.Ct. 2510. In this case, Congress drafted a precise, comprehensive litigation scheme for injuries sustained in a nuclear incident. The federal courts have recognized this congressional intent. O’Conner v. Commonwealth Edison Co., 13 F.3d 1090, 1099 (7th Cir.1994); In re TMI Litigation Cases, 940 F.2d 832, 854-55 (3d Cir.1991) (“In re TMI Litig.”). That scheme governs the conduct of this litigation. Congress enacted the PAA with twin goals in mind: to provide an incentive to contractors to participate in the nuclear industry by limiting their liability, and to compensate victims of nuclear accidents. See, e.g., Pub.L. No. 100-408, 102 Stat. 1066 (1988); S. Rep. No. 100-218, at 4-13 (1987), reprinted in 1988 U.S.C.C.A.N. 1476, 1479-88. The Act placed Plaintiffs’ state law claims in federal court and provided indemnification of Defendants from the federal government for any liability to victims of nuclear incidents. See 42 U.S.C. § 2210; S. Rep. No. 100-218, at 13, reprinted in 1988 U.S.C.C.A.N. at 1484, 1488. To allow those entitled to indemnity as government contractors to disclaim any liability because they are government contractors would be inconsistent with the goal of the PAA to provide compensation to victims of nuclear incidents. We will not assume that in enacting the PAA’s comprehensive scheme, Congress intended, yet failed to state in the Act, that victims of nuclear incidents cannot recover tort damages from nuclear operators when the operators were pursuing government goals. Accordingly, we hold that the government contractor defense is inapplicable as a matter of federal law and affirm the district court’s ruling on this key issue. TV. Strict Liability. Defendants next argue that the district court erred as a matter of Washington state law in holding Defendants strictly liable for any 1-131 emissions from the Hanford facility. Defendants challenge that ruling on three grounds: (1) that strict liability pursuant to Washington state law may not be imposed under the PAA if Defendants released 1-131 within federally-authorized emission levels; (2) even if state liability law applies, the Han-ford activity did not meet the “abnormally dangerous activity” test that warrants strict liability; and (3) even if Washington courts would apply a strict liability regime, Defendants would be exempted under the “public duty” exception that applies generally to heavily regulated entities doing potentially hazardous work. For the reasons below, we affirm the district court’s imposition of strict liability. A. Federally-Authorized Emissions. It is not disputed that the federal government is in charge of nuclear safety. “[T]he safety of nuclear technology [is] the exclusive business of the Federal Government,” which has “occupied the entire field of nuclear safety concerns.” Koller v. Pinnacle West Capital Corp., 2007 WL 446357, 2007 U.S. Dist. LEXIS 9186 (D.Ariz. Feb. 6, 2007) (second alteration in original) (quoting Pac. Gas & Elec. Co. v. State Energy Res. Conservation & Dev. Comm’n, 461 U.S. 190, 208, 212, 103 S.Ct. 1713, 75 L.Ed.2d 752 (1983)). Every federal circuit that has considered the appropriate standard of care under the PAA has concluded that nuclear operators are not liable unless they breach federally-imposed dose limits. See, e.g., O’Conner, 13 F.3d at 1105; In re TMI Litig., 940 F.2d at 859; Roberts v. Fla. Power & Light Co., 146 F.3d 1305, 1308 (11th Cir.1998); Nieman v. NLO, Inc., 108 F.3d 1546, 1553 (6th Cir.1997). Defendants are thus correct insofar as they point out that the clear weight of authority supports the principle that federal law preempts states from imposing a more stringent standard of care than federal safety standards. Strict liability may not be imposed for 1-131 releases within federally-authorized limits, because any federal authorization would preempt state-derived standards of care. To allow a jury to decide on the basis of a state’s reasonableness standard of care would “put juries in charge of deciding the permissible levels of radiation exposure and, more generally, the adequacy of safety procedures at nuclear plants- — issues that have explicitly been reserved to the federal government.” In re TMI Gen. Publ. Utils. Corp., 67 F.3d 1103, 1115 (3d Cir.1995) (citing Pacific Gas, 461 U.S. at 212, 103 S.Ct. 1713). This result would undermine the purpose of a comprehensive and exclusive federal scheme for nuclear incident liability. Defendants then go further, however, and argue that the district court in this ease permitted the jury to substitute its view of a reasonable emission standard for a government-standard. The problem with Defendants’ argument is that no federal standards governing emission levels existed at the time of the 1-131 emissions. Defendants try to remedy this problem by pointing to “tolerance doses” recommended and implemented by military and government scientists working on the Han-ford project and ask us to equate such recommendations with federally-authorized emission levels. They are not the same. These tolerance doses, although established under the aegis of the United States Army, did not carry the force of law and thus cannot provide the basis for a safe harbor from liability. They amounted to no more than site-specific safety rules. The United States Army instructed the Manhattan Engineering District to set forth standard, internal operating procedures for the plutonium-production process at Hanford. The tolerance doses were part of these procedures. The Met Lab scientists calculated what they thought were the outer limits of safe exposure at the plant. These internal guidelines were, however, exactly and only what they claimed to be: internal. They were not comprehensive, federal standards governing emission levels on which Defendants could rely to relieve them from liability for harm they caused. Defendants are correct that it would not have been possible for an agency to establish emission levels in the early 1940s, because the Atomic Energy Act was not enacted until 1954 and the Nuclear Regulatory Commission was created in 1974. In fact, the emissions occurred even prior to the enactment of the Administrative Procedure Act in 1946. This history, however, undermines Defendants’ position, because it highlights the absence of any federal machinery to promulgate legal standards on which Defendants could have reasonably relied to insulate them from liability to those living and breathing twenty-four hours a day in the area surrounding Hanford. The need for such standards was not recognized until many years later. B. Abnormally Dangerous Activity. Defendants next argue that even if state law standards apply in this case, the district court erred by holding that Washington tort law would impose strict liability. Specifically, Defendants contend that operating the Hanford facility does not constitute an “abnormally dangerous activity” under Washington law. We review de novo the question of whether an activity is abnormally dangerous, Langan v. Valicopters, Inc., 88 Wash.2d 855, 567 P.2d 218, 221 (1977), and we affirm. Washington has adopted the Restatement (Second) of Torts, sections 519 and 520, which outline the strict liability regime for abnormally dangerous activities. Klein v. Pyrodyne Corp., 117 Wash.2d 1, 810 P.2d 917, 920 (1991); New Meadows Holding Co. v. Wash. Water Power Co., 102 Wash.2d 495, 687 P.2d 212, 215 (1984). Section 519 provides: (1) One who carries on an abnormally dangerous activity is subject to liability for harm to the person, land, or chattels of another resulting from the activity, although he has exercised the utmost care to prevent such harm. (2) Such strict liability is limited to the kind of harm, the risk of which makes the activity abnormally dangerous. Section 520 lists the factors to be used when determining what constitutes an abnormally dangerous activity: (a) Whether the activity involves a high degree of risk of some harm to the person, land or chattels of another; (b) Whether the gravity of the harm which may result from it is likely to be great; (c) Whether the risk cannot be eliminated by the exercise of reasonable care; (d) Whether the activity is not a matter of common usage; (e) Whether the activity is inappropriate to the place where it is carried on; and (f) The value of the activity to the community. Restatement (Second) of ToRts §§ 519-20 (1977). A court does not have to weigh each of the elements listed in § 520 equally. Langan, 567 P.2d at 221. One factor, alone, however, is generally not sufficient to find an activity abnormally dangerous. Id. Defendants argue that at the time of the emissions in the 1940s, they did not know the risks that were attributable to radioiodine exposure, and therefore § 520’s factors (a)-(c) cannot be weighed against them. Any possible injury from radiation, however, need not have been actually known by Defendants at the time of exposure in order to impose strict liability. Under Washington law, if the actual harm fell within a general field of danger which should have been anticipated, strict liability may be appropriate. Whether an injury should have been anticipated does not depend on whether the particular harm was actually expected to occur. Koker v. Armstrong Cork, Inc., 60 Wash.App. 466, 804 P.2d 659, 667-68 (1991). It is sufficient that “the risk created [be] so unusual, either because of its magnitude or because of the circumstances surrounding it-” Langan, 567 P.2d at 221. There is no question that Defendants should have anticipated some of the many risks associated with operating a nuclear facility, creating plutonium, and releasing 1-131 into the atmosphere. It is exactly because of these risks, and the potential exposure to liability arising from them, that the government contracted with Defendants to limit liability in case of an accident. For these same reasons, the Met Lab scientists recommended dosage limits. We agree with the district court that Defendants’ conduct at Hanford was an abnormally dangerous activity under the § 520 factors. There was a high degree of risk to people and property associated with the Hanford facility and the gravity of any harm was likely to be great. See Restatement (Second) of ToRts § 520. Regardless of Defendants’ efforts to exercise reasonable care, some 1-131 would be released, and developing plutonium is hardly an activity of common usage. While the value to the community at large, i.e., the nation, of developing an atomic bomb was perceived as high and there is pragmatically no very appropriate place to carry on such an activity, the § 520 factors on balance support holding that Defendants’ activities were abnormally dangerous. C. Public Ditty Exception to Strict Liability. Defendants’ final defense is that even if their conduct constituted an abnormally dangerous activity, they are exempted from strict liability under Washington law pursuant to the “public duty” exception. See Restatement (Seoond) of ToRts § 521. While this issue presents a close question, we conclude that Defendants do not qualify for the exception. Section 521 of the Restatement provides: The rules as to strict liability for abnormally dangerous activities do not apply if the activity is carried on in pursuance of a public duty imposed upon the actor as a public officer or employee or as a common carrier. Id. As a threshold matter, Washington courts have not yet adopted § 521. We must therefore decide what the Washington Supreme Court would likely do if confronted with the issue. See NLRB v. Calkins, 187 F.3d 1080, 1089 (9th Cir.1999). We hold that the court would likely adopt the public duty exception. Although they have never explicitly adopted § 521, Washington courts have adopted § 519, which governs abnormally dangerous activities generally. The comments to § 519 indicate that the public duty exception is part and parcel of strict liability. Comment “a” to § 519 states that “[t]he general rule stated in this Section is subject to exceptions and qualifications, too numerous to be included within a single section. It should therefore be read together with §§ 520 to 524A, by which it is limited.” Restatement (SECOND) of Torts, § 519 cmt. a. Comment “d” further limits the scope of strict liability and states that persons are accountable only for abnormally dangerous activities they undertake “for [their] own purposes.” Id. § 519 cmt. d. A key corollary to this point is that strict liability does not apply to activities carried on in pursuance of a public duty the actor was legally obligated to perform. See id. § 521. Although Washington could adopt § 519 without adopting the numerous exceptions found in §§ 521-524A, it is unlikely that it would do so. Washington adopted wholesale the abnormally dangerous activity doctrine and its exceptions when they existed in the First Restatement. See, e.g., Epperly v. Seattle, 65 Wash.2d 777, 399 P.2d 591, 595 (1965); Foster v. Preston Mill Co., 44 Wash.2d 440, 268 P.2d 645, 647 (1954). Furthermore, of the states that have adopted §§ 519-20, the vast majority has also adopted the subsequent exceptions. Although widely adopted, the courts that have applied the public duty exception have generally done so only to the extent a defendant was legally required to perform the ultrahazardous activity. See Restatement (Seoond) op ToRts, § 521, cmt. a. The Washington Supreme Court’s decision in Siegler v. Kuhlman, 81 Wash.2d 448, 502 P.2d 1181 (1972), supports such an application of the public duty doctrine here. The defendants in Siegler were a trucking company for Texaco and its driver, and the company was not legally obligated as a common carrier to carry materials that eventually caused an explosive, fatal accident on a highway. The Washington court held that the activity was abnormally dangerous and that the defendants could be held strictly liable for the accident. It is therefore most likely that the Washington Supreme Court would apply strict liability when the defendant was performing a dangerous activity for “his own purpose,” and would apply the public duty exception only in the appropriate case when the defendant was engaged in a legally-obligated activity, such as a regulated common carrier bound to carry hazardous substances. Defendants argue that in light of the exceptional and patriotic circumstances under which they operated Hanford, we should treat them as analogous to public employees who would qualify for the exception. Although Defendants are correct that we generally do not parse the language of a restatement as meticulously as that of a statute, and we will apply it “when the purposes it seeks to serve dictate its application,” McKay, 704 F.2d at 447, Defendants do not satisfy the exception’s purpose in this case. Defendants are not public officers or employees or common carriers, see Restatement (Second) of ToRts § 521, and they were not legally obligated to operate Hanford. The prototypical example of a defendant entitled to the public duty exception is a utility company that is legally required to transport an ultrahazardous good, such as electricity, and causes injury to someone during transport. Courts have recognized a public duty exception in such cases, because common carriers must accept, carry, and deliver all goods offered to them for transport within the scope of the operating authority set forth in their permits. See, e.g., 16 U.S.C. § 824 et. seq. (granting the Federal Energy Regulatory Commission authority to establish guidelines for common carriers of electricity in interstate commerce); United States v. W. Processing Co., 756 F.Supp. 1416, 1421 (W.D.Wash.1991). They cannot discriminate against customers or refuse to accept commodities that may be dangerous for transport. Id. The case law therefore illustrates that the duty involved is the legal obligation to perform the abnormally dangerous activity in accordance with government orders. See, e.g., EAC Timberlane v. Pisces, Ltd., 745 F.2d 715, 721 n.12 (1st Cir.1984) (noting that the public duty must be one imposed on the actor) (citing Actiesselskabet Ingrid v. Central R.R. Co. of New Jersey, 216 F. 72 (2d Cir.1914); Town of East Troy v. Soo Line R.R. Co., 409 F.Supp. 326, 329(E.D.Wis.1976) (no strict liability for spillage of carbolic acid by derailment of common carrier train)); Christ Church Parish v. Cadet Chem. Corp., 25 Conn. Supp. 191, 199 A.2d 707, 708-09 (1964) (transportation of twenty tons of various chemical substances); Pecan Shoppe of Springfield v. Tri-State Motor Transit Co., 573 S.W.2d 431, 438-39 (Mo.Ct.App.1978) (transporter of explosives); Pope v. Edward M. Rude Carrier Corp., 138 W.Va. 218, 75 S.E.2d 584, 595-96 (1953) (transporter of explosives). Qualifying entities must be operating pursuant to the mandate and control of the government; they must have little discretion over the manner in which they conduct their activities. See Actiesselskabet Ingrid, 216 F. at 78(“It certainly would be an extraordinary doctrine for courts ... to say that a common carrier is under legal obligation to transport dynamite and is an insurer against any damage which may result in the course of transportation, even though it has been guilty of no negligence which occasioned the explosion which caused the injury.”); Pope, 75 S.E.2d at 591-92 (holding no strict liability for common carrier transport of explosives); but see Lamb v. Martin Marietta Energy Sys., Inc., 835 F.Supp. 959 (W.D.Ky.1993) (applying the public duty exception to a nuclear facility because under Kentucky law the public duty exception includes entities engaged in activities of public necessity even when there is no legal duty to perform them). There was no government mandate here. The events giving rise to this litigation occurred before the government developed rules or the ability to control nuclear facilities. The government was relying on the expertise of defendants and not vice versa. We should not confuse the legal concept of a public duty with popular notions of patriotic duty taken at personal sacrifice. Defendants may well have been acting at the government’s urging during wartime. The public duty exception, however, was developed under state law in recognition of the need to protect private actors who are legally required to engage in ultrahazar-dous activities. No matter how strongly Defendants may have felt a patriotic duty, they had no legal duty to operate Hanford, and they are, therefore, not entitled to the public duty exception. The district court correctly found defendants subject to strict liability. V. Statute of Limitations. A Waiver. Defendants argue for the first time on appeal that Bellwether Plaintiff Gloria Wise’s lawsuit was untimely, because pursuant to Am. Pipe & Constr. Co. v. Utah, 414 U.S. 538, 94 S.Ct. 756, 38 L.Ed.2d 713 (1974), Wise lost the benefit of any statute of limitations tolling when she filed a separate, individual suit prior to the denial of class certification. Defendants arguably have waived this claim, because they did not raise the issue below sufficiently for the district court to rule on the matter. McMillan v. United States, 112 F.3d 1040, 1047 (9th Cir.1997); In re E.R. Fegert, Inc., 887 F.2d 955, 957 (9th Cir.1989). We have discretion, however, to overlook any waiver. See United States v. Bynum, 327 F.3d 986, 990 (9th Cir.2003). We exercise such discretion in this case, because the issue of whether Wise’s lawsuit was tolled pending class certification is a purely legal question, see id.; both parties concede that the issue is “important,” and addressing the issue is consistent with the purpose of a bellwether trial in clarifying and stream-lining the relevant issues. The issue should therefore be settled now. We recognize that the results of the Hanford bellwether trial are not binding-on the remaining' plaintiffs. See, e.g., In re Hanford Nuclear Res. Litig., No. 91-03015, Dkt. # 1294 at 164-65 (E.D.Wash. June 3, 2003). Nevertheless, according to counsel for the parties, the purpose of the bellwether trial was to “establish the relative strengths and weaknesses of the parties, spread out mainly for settlement purposes.... ” Id. at 155, 165. The bellwether trial was meant to be a “learning process.” Id. at 161. The parties also state in their briefs that there are “numerous” other plaintiffs who face a similar statute of limitations hurdle. It would defeat the purpose of a bellwether trial and only deter settlement longer to refrain from deciding this purely legal issue at.the earliest possible stage. Our resolution will save any potentially time-barred plaintiffs from expending additional resources and energy on futile legal proceedings. B. Application of American Pipe. In April 1994, the Hanford plaintiffs moved for class certification. The district court reserved ruling on certification under the opt-out provision of Federal Rule of Civil Procedure 23(b)(3). Plaintiffs eventually withdrew their request for certification, but not until May 2003, after the first series of appeals was decided by this circuit. Accordingly, the district court held that the statute of limitations was tolled for all putative class members from April 1994 until May 2003. Plaintiff Wise was diagnosed with thyroid cancer in April 1993, three years after the first class action complaints were filed and one year before Plaintiffs moved for class certification. Wise filed an individual suit in district court in July 1997. If the date of diagnosis is the triggering date for the statute of limitations, her individual suit was apparently untimely, because Washington’s statute of limitations for personal injury claims is three years. Wise’s suit would have been timely only if she was entitled to the tolling that began for the class action plaintiffs on April 15, 1994. Defendants now contend that Wise forfeited these tolling benefits when she filed her individual suit prior to the district court granting or denying class certification. Wise contends she is entitled to tolling as a member of the class pursuant to American Pipe. In American Pipe, 414 U.S. at 554, 94 S.Ct. 756, the Supreme Court held that the commencement of a class action suspends the applicable statute of limitations as to all asserted members of the class who would have been parties had the suit been permitted to continue as a class action. Id. The tolling period ends, and the statute runs anew, once class certification is granted or denied. Tosti v. City of Los Angeles, 754 F.2d 1485, 1488 (9th Cir.1985). The issue in this case, which is one of first impression in our circuit, is whether American Pipe also permits tolling for a plaintiff who files a separate action pending class certification. The overwhelming weight of authority answers the question in the negative. The Sixth Circuit, which is the only circuit to have addressed the issue directly, has also said no. It held that the purposes of class action tolling under American Pipe “are not furthered when plaintiffs file independent actions before decision on the issue of class certification.” Wyser-Pratte Mgmt. Co., Inc. v. Telxon, 413 F.3d 553, 569 (6th Cir.2005). Such purposes are only furthered “when plaintiffs delay until the certification issue has been decided.” Id. The Second Circuit tangentially reached a similar conclusion two decades earlier, when it stated that “[t]he policies behind Rule 23 and American Pipe would not be served, and in fact would be dis-served, by guaranteeing a separate suit at the same time that a class action is ongoing.” Glater v. Eli Lilly & Co., 712 F.2d 735, 739 (1st Cir.1983). Countless federal district courts have come to the similar conclusion that “[applying the tolling doctrine to separate actions filed prior to class certification would create the very inefficiency that American Pipe sought to prevent.” In re WorldCom, Inc. Sec. Litig., 294 F.Supp.2d 431, 451 (S.D.N.Y.2003) (citing cases); see also In re Heritage Bond Litig., 289 F.Supp.2d 1132, 1150 (C.D.Cal.2003). We share the prevailing view that precluding tolling in this situation satisfies the judicial economy concerns of American Pipe without jeopardizing protections that exist for plaintiffs who opt out of the class. We should not allow a plaintiff to file an individual suit, which is in essence a signal that the plaintiff is opting out of a class, and then simultaneously give the same plaintiff class action benefits. “The parties and courts [should] not be burdened by separate lawsuits which 9820 ... may evaporate once a class has been certified.” Wyser-Pratte, 413 F.3d at 569(quoting In re WorldCom, 294 F.Supp.2d at 452). Courts have recognized that class action tolling is intended to avoid the injustice of requiring putative class members to file individual suits or to lose their claims, but the benefits should not be abused. Tolling is not “intended to be a tool to manipulate limitations periods for parties who, intending all along to pursue individual claims, assert reliance on the proposed class action just long enough to validate their otherwise time barred claims.” Rahr v. Grant Thornton, LLP, 142 F.Supp.2d 793, 800 (N.D.Tex.2000). Accordingly, we hold that this individual who filed a separate suit pending a decision on class certification loses the benefit of any statute of limitations tolling under American Pipe. On the record before us, we are unable to determine whether Plaintiff Wise’s individual suit was timely absent American Pipe tolling, because we do not know the triggering date under Washington law for the statute of limitations in her case. We therefore remand to the district court for further proceedings on this issue .consistent with our opinion. VI. Medical Monitoring Claims. Plaintiffs Pamela Durfey, Paulene Echo Hawk, and Dorothy George’s only claim on appeal is for medical monitoring. They do not yet have any diseases attributable to Hanford radiation. Because in all relevant respects Plaintiffs are analogous to the plaintiffs who requested medical monitoring in 2002 in Berg, 293 F.3d 1127, Plaintiffs’ claims were originally stayed pending this court’s decision in that case. We then decided Berg, in which we held that claims for medical monitoring are not compensable under the PAA, because they do not constitute claims of “bodily injury, sickness, disease, or death ...” Berg, 293 F.3d at 1132-33(citing 42 U.S.C. § 2014(q)). After our decision, Plaintiffs in this case asked the district court to remand their medical monitoring claims to state court. They claimed that Berg abrogated subject matter jurisdiction in federal court for all medical monitoring claims. Defendants opposed remand, arguing that Berg did not remove the district court’s subject matter jurisdiction, but held only that a medical monitoring claim was not cognizable under the PAA. Although in Berg we referred to bodily injury as a jurisdictional prerequisite, id. at 1131-33, we used the term “jurisdictional” in the loose sense, perhaps too loose, to mean that medical monitoring claims were not compensable under the PAA. We have been guilty of such expansive use of the term before. See Khalsa v. Weinberger, 779 F.2d 1393, 1396 n. 2 (9th Cir.1985) (“... jurisdiction has many possible meanings, ranging from subject matter jurisdiction to the power to grant the relief requested ... ”). The district court in this case clearly had subject matter jurisdiction under the PAA to decide the issue; the district court simply did not have the power to grant the relief requested. See id. The PAA is the exclusive means of compensating victims for any and all claims arising out of nuclear incidents. Berg, 293 F.3d at 1132; In re TMI Litig., 940 F.2d at 854; see also 42 U.S.C. § 2014(hh), (w)(federal courts have jurisdiction over public liability actions, defined as “any suit asserting ... any legal liability arising out of or resulting from a nuclear accident”) (emphasis added). This result is consistent with Congress’s explicit intent in enacting the 1988 Amendments and avoiding piecemeal litigation arising from nuclear incidents. We therefore affirm the district court’s exercise of jurisdiction over Plaintiffs’ medical monitoring claims and its conclusion pursuant to our decision in Berg that they were not compensable under the Act. The district court properly denied Plaintiffs’ request for a remand to state court. VII. First Bellwether Trial. The remaining issues on appeal stem from a variety of legal and evidentiary rulings in the two trials. Three of the six Bellwether Plaintiffs, Goldbloom, Buckner, and Carlisle, lost at the first trial. Three of their evidentiary challenges constitute reversible error; the remaining arguments are meritless. A. Causation. We first decide whether under Washington law the district court properly instructed the jury in the bellwether trial on “but-for,” and not “substantial factor,” causation. Plaintiffs contend that the more lenient substantial factor test should apply because other factors could have contributed to their illnesses, such as smoking and genetics. We review the district court’s application of Washington law de novo, Ostad v. Or. Health Scis. Univ., 327 F.3d 876, 883 (9th Cir.2003), and we affirm the district court’s instruction on but-for causation. Under the PAA, Washington state law controls the standard of causation to be used in this case. See 42 U.S.C. § 2014(hh). (“A public liability action shall be deemed to be an action arising under section 170 [42 U.S.C. § 2210], and the substantive rules for decision in such action shall be derived from the law of the State in which the nuclear incident involved occurs, unless such law is inconsistent with the provisions of such section.”). Washington courts will depart from the standard but-for causation instruction in favor of the substantial factor test only in three rare circumstances: (1) the plaintiff was excusably ignorant of the identity of the tortfeasor who caused his injury; (2) the plaintiff probably would have been injured anyway, but lost a significant chance of avoiding the injury; or (3) the plaintiff has been injured by multiple independent causes, each of which would have been sufficient to cause the injury. Gausvik v. Abbey, 126 Wash.App. 868, 107 P.3d 98, 108 (2005); see also Daugert v. Pappas, 104 Wash.2d 254, 704 P.2d 600, 605-06 (1985). The parties agree that the first and second exceptions are not at issue here. Plaintiffs know the identity of the tortfea-sors and had no chance to avoid injury. See, e.g., Lockwood v. AC & S, Inc., 109 Wash.2d 235, 744 P.2d 605, 613 (1987) (applying the substantial factor test when there is no doubt that asbestos was the cause of a plaintiffs asbestosis, but the plaintiff cannot identify which manufacturer is responsible); Mavroudis v. Pittsburgh Corning Corp., 86 Wash.App. 22, 935 P.2d 684, 687 (1997). Plaintiffs therefore appear to rely on the third type of substantial factor causation, which applies when there have been “multiple, independent causes,” each of which alone is sufficient to cause the injury. Gausvik, 107 P.3d at 108. There are two requirements they must satisfy (1) there must have been multiple causes of the injury; and (2) any one cause alone was sufficient to cause the injury. Id. Plaintiffs can not satisfy the second requirement. Plaintiffs instead ask us to expand the substantial factor doctrine and apply the test when there are potentially multiple causes of each plaintiffs injury, such as radiation, smoking, genetics, or pregnancy, even though Plaintiffs cannot show that Hanford radiation alone would have been sufficient to cause the injury. Their reading of Washington law would allow the substantial factor test to supplant but-for causation in virtually all toxic tort cases. Such a result is inconsistent with existing Washington law, which applies the substantial factor test in very limited circumstances. See also RESTATEMENT (THIRD) OF TORTS § 26 cmt. j (Proposed Final Draft 2005) (eliminating the substantial factor test). We therefore hold that the district court properly instructed the jury on but-for causation. B. Evidentiary Rulings Constituting Reversible Error. i. Cross-Examination of Dr. Davies. Plaintiffs raise two issues with respect to Defendants’ cross-examination of Plaintiffs’ endocrinologist expert Dr. Terry Davies, in the first bellwether trial. The first issue concerns the district court’s ruling that Dr. Davies could not testify that he authored articles on I-131’s effect on thyroid cells. The second issue is Defendants’ cross-examination of Dr. Davies with deposition testimony of a non-testifying expert. These errors surrounding Dr. Davies’ testimony, taken together, were prejudicial to Plaintiffs’ case. We therefore must remand for a new trial. With respect to Dr. Davies’ pre-litigation scholarship, the district court barred Plaintiffs from asking him whether he has “published any peer reviewed articles or papers regarding the capacity of I-131 to kill or damage thyroid cells.” The record reveals that the district court believed Dr. Davies could not testify about any pre-litigation articles on this subject, because Dr. Davies had not written any peer-reviewed scientific article concluding that doses at less than 100 rads can cause autoimmune disease. This ruling was an abuse of discretion, because it deprived the jury of testimony from Dr. Davies about the extent of his pre-litigation expertise regarding causes of thyroid illness. That Dr. Davies had not written any articles specifically directed to causation below 100 rads does not mean Dr. Davies’ work on causation generally was inadmissible. Plaintiffs’ key witness on causation extensively researched and authored scholarship on the capacity of 1-131 emissions to kill thyroid cells, and the jury was entitled to know the reach of his expertise. Standing alone, this error might not be prejudicial; there is, however, a more serious problem with the presentation of Dr. Davies’ testimony. Defendants were allowed to impeach one of Plaintiffs’ key expert witnesses with inadmissible evidence, hearsay statements that Defendants themselves successfully excluded from Plaintiffs’ case-in-chief. Prior to trial, Plaintiffs proffered the deposition testimony of epidemiologist Dr. A. James Ruttenber. According to Plaintiffs, Dr. Ruttenber would have testified that although current epidemiological studies prove only that radiation above 40 rads can cause thyroid disease, those studies do not preclude causation at lower dosages. On Defendants’ motion, the district court excluded this testimony, finding it was too speculative. Having learned that the most probative part of Dr. Ruttenber’s testimony was no longer admissible, Plaintiffs chose not to call him to the stand. Plaintiffs, instead, called Dr. Davies to testify that low dosages of radiation could cause thyroid disease. Dr. Davies had relied on some of Dr. Ruttenber’s dosage estimates in preparing his pretrial expert report, but he never read nor relied on Dr. Ruttenber’s deposition in rendering his expert opinion. Even though Dr. Rut-tenber’s causation testimony has been ruled inadmissible prior to trial, defense counsel on cross-examination used Dr. Ruttenber’s deposition to impeach Dr. Davies’ testimony. Among many other questions, defense counsel asked the following regarding Dr. Ruttenber’s deposition: Q: And doctor, are you aware that Doctor Ruttenber has said that the epidemiological literature can only show an increased risk of autoimmune thyroiditis down to 40 rads?.... Q: Did Doctor Ruttenber ever identify to you any epidemiological studies that reported that doses at 10 rad increased the risk of autoimmune thyroid disease? Q: Yeah, and page 75 at the bottom, lines 23 to 25, “Doctor Ruttenber, is it your testimony that the epidemiology gets you down to increased risk of autoimmune thyro