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. e du/thir dc ir c uit_1999/30Filed February 3, 1999

UNITED STATES COURT OF APPEALS

FOR THE THIRD CIRCUIT

_______________

NO. 97-1735

_______________

CAROL HELLER; THOMAS HELLER individually and as the parents and natural guardians of EMILY HELLER a nd KATHERINE HELLER, minor children, Appellants

v.

SHAW INDUSTRIES, INC.

_______________

On Appeal from the United States District Court For the Eastern District of Pennsylvania (D.C. Civ. No. 97-07657) District Judge: Honorable William H. Yohn, Jr.

_______________

Argued: October 6, 1998 Before: BECKER, Chief Judge, NYGAARD, and NOONAN,* Circuit Judges

(Filed: February 3, 1999)

JOSEPH C. KOHN, ESQUIRE JOANNE ZACK, ESQUIRE (ARGUED) MARTIN J. D'URSO, ESQUIRE

DAVID G. CONCANNON, ESQUIRE Kohn, Swift & Graf, P.C. 1101 Market Street, 24th Floor Philadelphia, PA 19107

Attorneys for Appellants

___________________________________________________ ____ *Honorable John T. Noonan, Jr., Senior Judge of the United States Court of Appeals for the Ninth Circuit, sitting by designation.

JOHN F. KENT, ESQUIRE ANNE M. MANERO, ESQUIREKent & McBride

18th & Arch Streets Two Logan Square, Suite 600 Philadelphia, PA 19103

LEE ANN JONES, ESQUIRE (ARGUED) Powell, Goldstein, Frazer & Murphy,

LLP

191 Peachtree Street Atlanta, GA 30303

Attorneys for Appellee

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OPINION OF THE COURT

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BECKER, Chief Judge:

This is an appeal by plaintiff Carol Heller ("Helle r"), who sought to recover from defendant Shaw Industries (" Shaw"), for certain respiratory illnesses allegedly caused by volatile organic compounds emitted by Shaw carpet installed in Heller's former home. The District Court's grant of summary judgment against Heller and in favor of Shaw is lar gely a function of its exclusion, following an extensive i n limine hearing, of key expert testimony by which Heller ho ped to establish liability. See Heller v. Shaw Indus., Inc ., No. Civ.A.95-7657, 1997 WL 535163 (E.D. Pa. Aug. 18, 19 97). In reviewing the District Court's rulings, we revisit the caselaw interpreting Federal Rule of Evidence 702, particul arly Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U .S. 579 (1993), and In re Paoli Railroad Yard PCB Litigatio n, 35 F.3d 717 (3d Cir. 1994), and apply their teachings to th is case.

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After careful but deferential review, see General E lec. Co. v. Joiner, 118 S. Ct. 512, 517 (1997), we conclude tha t, although the District Court erred in excluding cert ain aspects of the experts' proffered testimony, it properly ex cluded the central portions of their testimony, depriving Hell er's claim of its needed evidentiary support.

More specifically, the District Court was too restr ictive in requiring Heller's medical expert to rely on publis hed studies specifically linking Heller's illness with Shaw's p roduct, and in requiring Heller's medical expert to rule out al l alternative possible causes of her illness. However, it properl y excluded this expert's causation testimony because his concl usion regarding the cause of Heller's illness was heavily based on a flawed temporal relationship between the installa tion of theShaw carpet and the presence of Heller's illness. T he District

Court also properly excluded the testimony of Helle r's environmental expert on the grounds that his enviro nmental testing revealed levels of dangerous compounds in t he air in Heller's home that were not significantly higher th an background levels, and his methodology for extrapol ating from these tests to estimate the (higher) levels of compounds at an earlier time was seriously flawed. Therefore, because

the District Court did not abuse its discretion in excluding the key elements of Heller's experts' testimony nec essary to prove causation, the grant of summary judgment will be

affirmed.

I. Facts and Procedural History

On September 30, 1993, Heller, her husband Thomas, and their two children moved into a nine-year old house in West Chester, Pennsylvania. Shortly after the move, Thom as Heller experienced allergy symptoms. In November and Decem ber 1993, an allergist advised Mr. Heller to replace th e carpeting in the home because cat hair from previous owners m ight have caused his allergic reactions. On December 13 and 14, 1993, the Hellers put new carpeting--manufactured b y Shaw Industries--in certain rooms of their home, includi ng the

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master bedroom on the first floor and a guest room on the

second floor.

In late December 1993, Carol Heller began to experi ence respiratory problems, including asthma, breathing d ifficulty, wheezing, coughing, and dizziness. After seeking tr eatment from her father, a physician, Heller consulted Dr. Joseph Papano, an allergist and one of her two expert witn esses.1 Her first visit to Dr. Papano was on February 15, 1994. Dr. Papano took Heller's medical and family history, qu estioned her about her environment (whether there were cats or dogs in the home, etc.), and performed allergy tests, ch est X-rays, and pulmonary function tests. Based on the history, tests, and a physical examination, Dr. Papano ruled out va rious possible causes of her respiratory problems. In Feb ruary 1994, the doctor recommended that Heller contact Al an Todd of Todd Environmental Consultants (collectively "To dd") to test both the air quality in her home and the carpe t.2 When Dr. Papano next saw Heller, on March 19, 1994, she was still experiencing problems, but informed him that her sy mptoms

___________________________________________________ ____

1. Because, as discussed below, Dr. Papano relied h eavily for his diagnosis on the temporal relationship between theinstallation of the Shaw carpet and the onset of He ller's

illness, the date on which she began to experience her symptoms is a contested and important issue. Dr. Papano orig inally testified at his deposition that her symptoms began in "January 1994," and he so stated in his expert witness repor t. However, at the Daubert hearing, he testified that the symptoms began in "mid-January 1994." Heller testified at the Daubert hearing that her symptoms began in late December 1993 or early J anuary 1994, while her father testified that they began either i n mid-December or during the first two weeks of December. Given th e conflicting testimony, we find no clear error in the District C ourt's reliance, in its findings following the Daubert hea ring, on Heller's testimony that her symptoms began in late December 1993. See Heller, 1997 WL 535163, at *17 n.29.

2. Dr. Papano's expert report represents that he re ferred Heller to Todd at her March 1994 visit, while Todd's exper t report states that he was first contacted by Heller and di d the initial testing in February. The District Court apparently credited Todd and we will not revisit this (supported) conclusion . Given that the initial home testing was performed by Todd in F ebruary 1994, Dr. Papano must have referred the Hellers to Todd i n February.

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improved when she was out of her house. At this tim e, she brought the doctor a sample of the Shaw carpet, whi ch he testified had a strong odor.

The Hellers contracted with Todd to perform the tes ting of the environment in the house and of the carpet. Tod d initially tested for excessive levels of dust or other possib le contaminants, finding nothing unusual. By April 7, 1994, the Heller family had moved out of their home in an att empt to eliminate Heller's respiratory problems. On April 1 4, 1994,

Todd tested the air in the closet of one of the Hel lers' bedrooms; the closet contained both some of the Sha w carpet and some carpet from an unknown manufacturer. Todd' s initial test, conducted over approximately eight ho urs, found fourteen types of volatile organic compounds ("VOC" s) present

in the air in the closet.

Three weeks later, on May 5, 1994, the Shaw carpet was removed from the house. Less than a week later, on May 11, 1994, Todd again tested the air in the bedroom clos et for eight hours. During the period between the two test s, no other changes were made in the house: no objects we re added or removed, the windows remained closed, and no per sons entered or left the by-now empty house. In the seco nd test, Todd found only five types of VOCs present. Four of these were present in levels virtually indistinguishable from the initial readings. Therefore, nine compounds complet ely disappeared and one (benzene) remained present, but atlower levels. Todd's initial conclusion, in a May 2 3, 1994,

letter to Heller, was that "none of the compounds i dentified would be expected to typically result in asthmatic or sensitization responses." (Later, however, in his f irst expert witness report, dated January 16, 1997, he opined t hat the compounds that disappeared or diminished were emitt ed from the Shaw carpet, and were "the likely source o f [the Hellers'] irritation and related responses.")

The Hellers returned to the home briefly on May 11, 1994. Although the carpet had been removed six days earli er and the May 11 testing would reveal the presence of ver y few

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VOCs, Mrs. Heller again experienced "wheezing, shor tness of

breath and an irritated throat." The Hellers then l eft the house, never to return. In November 1994, they sold the home for less than they had paid for it a year earl ier.

Dr. Papano's expert report stated that he performed a differential diagnosis, which involved ruling out p ossible causes of Heller's symptoms other than Shaw's carpe t (including "an infectious cause"), and, based large ly on the temporal relationship between her symptoms and the installation of the Shaw carpet, concluded that the Shaw carpet precipitated Heller's respiratory problems. As noted above, Alan Todd also offered his expert opinion (i n his original expert report) that "to a reasonable degre e of scientific certainty, . . . the illness[es] suffere d by the Heller family were caused by their prolonged exposure to t he VOC's measured in their home and emitted by the carpeting manufactured by Shaw Industries."

In December 1995, the Hellers brought a diversity a ction against Shaw in the District Court for the Eastern District of Pennsylvania, under 28 U.S.C. S 1332, alleging brea ch of warranty, failure to warn, negligent and intentiona l misrepresentation, defective design, and violation of state consumer protection laws. The complaint sought compensatory and punitive damages for both personal injuries and property damage, as well as a medical monitoring award. To establish defective design and failure to warn, a plaintiff must prove that the defendant's p roduct caused her injuries. Causation therefore was the pr imary focus of the District Court's inquiry and the prima ry disputed

issue in this case.

Following extensive discovery, Shaw moved for summa ry judgment and, as an adjunct to that motion, moved i n limine to exclude all of Heller's expert witness testimony . The District Court held a Daubert hearing over several days. It then filed an unpublished opinion and order, granti ngdefendant's motions for exclusion of plaintiff's ex pert

testimony and for summary judgment. See Heller v. S haw

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Indus., Inc., No. Civ.A.95-7657, 1997 WL 535163 (E. D. Pa. Aug. 18, 1997).

On appeal, we review a District Court's decision to exclude expert testimony for abuse of discretion. See Joine r, 118 S. Ct. at 517. The District Court's interpretation of the requirements of Rule 702, however, is subject to pl enary review. See Paoli, 35 F.3d at 749. As to the Distri ct Court's entry of summary judgment for defendants, "we exerc ise plenary review, construing all evidence and resolvi ng all doubts raised by affidavits, depositions, answers t o interrogatories, and admissions on file in favor of the nonmoving party." Iberia Foods Corp. v. Romeo, 150 F. 3d 298, 302 (3d Cir. 1998).

Heller does not appear to dispute that, if we deter mine that the District Court properly excluded all of plainti ff's expert testimony, summary judgment for defendant was the p roper course for the key claims of design defect and fail ure to warn. This is because, without either Dr. Papano's or Ala n Todd's testimony, Heller would be left without any proof o f causation, a necessary element for each of these cl aims. However, if we decide (as we do) that some of the t estimony should have been admitted, we must determine whethe r that testimony is sufficient to create a material issue of fact on the causation issue. Most of our opinion will focus on the key underlying issue of the admissibility of Heller's e xpert witness testimony, on which the causation issue hinges. Whi le there are other issues in the case, including breach of w arranty and misrepresentations, we will address these only briefly, for they are easily disposed of without extended discus sion.

II. Expert Witnesses: The Legal Background

Rule 702 provides: "If scientific, technical, or ot her specialized knowledge will assist the trier of fact to

understand the evidence or to determine a fact in i ssue, a witness qualified as an expert . . . may testify th ereto in the form of an opinion or otherwise." Relying on the la nguage of

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Rule 702 and the liberal thrust of the Federal Rule s of Evidence, the Supreme Court held in Daubert that ex pert testimony need be based only on a reliable and scie ntifically valid methodology that fits with the facts of a cas e. See Daubert, 509 U.S. at 592-93.3 The Court listed four factors to guide a district court in its preliminary assessmen t of theserequirements, but cautioned that these were guidepo sts and

not required factors in each case. The factors are: (1) whether the methodology can and has been tested; (2) whethe r the technique has been subjected to peer review and pub lication; (3) the known or potential rate of error of the met hodology; and (4) whether the technique has been generally ac cepted in the proper scientific community. See id. at 593-94. The Court made clear that its listing of these factors should not obscure the fact that the district court's gatekeeper role is a flexible one, see id. at 594 & n.12, and that the factors ar e simply useful signposts, not dispositive hurdles that a pa rty must overcome in order to have expert testimony admitted . In this regard, a party seeking to exclude (or to admit) ex pert testimony must do more than enumerate the factors f rom Daubert (and the additional ones from Paoli, discus sed below) and tally the number that are or are not met by a p articular expert's testimony.

In Daubert, the Court noted that "[v]igorous crossexamination, presentation of contrary evidence, and careful instruction on the burden of proof are the traditio nal and appropriate means of attacking shaky but admissible evidence," and that, even if expert testimony is ad mitted, summary judgment might be warranted if a party has still failed to present sufficient evidence to get to the jury. Id. at 596; see also Paoli, 35 F.3d at 750 n.21. Clearly, the Court envisioned cases in which expert testimony meets th e Daubert standard yet is "shaky," and cases in which

___________________________________________________ ____

3. In Daubert, the Supreme Court interred the decad es-old Frye doctrine,from Frye v. United States, 293 F. 1013 (D .C. Cir. 1923), which required that an expert's methodology be "generally accepted" within the scientific community before th e expert's testimony could be admitted. See Daubert, 509 U.S. at 588-89.

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admissible expert testimony provides only a "scinti lla" of support for a claim or defense. Put differently, an expert opinion must be based on reliable methodology and m ust reliably flow from that methodology and the facts a t issue-- but it need not be so persuasive as to meet a party 's burden of proof or even necessarily its burden of producti on.

In Paoli, filed barely a year after Daubert, we ide ntified a number of factors that a istrict court might use in evaluating expert testimony in addition to the four factors

listed in Daubert. The additional factors include: (1) "the existence and maintenance of standards controlling the technique's operation"; (2) "the relationship of th e techniqueto methods which have been established to be reliab le"; (3)

the expert witness's qualifications; and (4) "the n on-judicial uses to which the method has been put." Paoli, 35 F .3d at 742 n.8. In Paoli, we explained that even if the ju dge believes "there are better grounds for some alternative conc lusion,"

and that there are some flaws in the scientist's me thods, if there are "good grounds" for the expert's conclusio n, it should

be admitted. Id. at 744.4

We also emphasized in Paoli that the district court could not exclude the testimony simply because the conclu sion was "novel" if the methodology and the application of t he methodology were reliable. See id. at 746 n.15. How ever, we rejected the plaintiffs' argument in Paoli (also ur ged strongly by the plaintiff here) that the district court had abused its discretion by examining the experts' conclusions. W hile "[t]he focus, of course, must be solely on principles and methodology, not on the conclusions that they gener ate," Daubert, 509 U.S. at 595, a district court must exa mine the expert's conclusions in order to determine whether they could

___________________________________________________ ____

4. In addition to the "good grounds" requirement, i n a diversity case such as this, state rules on the degree of cer tainty required of an expert's opinion apply. In Pennsylva nia, a doctor can give an opinion on the cause of a plaintiff's i llness if he or she can do so with a reasonable degree of medica l certainty. See Paoli, 35 F.3d at 750-52.

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reliably follow from the facts known to the expert and the methodology used.5

III. Plaintiff's Expert Witnesses

In this case, Heller must demonstrate, as part of h er prima facie case, that Shaw's carpet emitted VOCs into th e air; that she inhaled these VOCs; that she has an injury; and that the VOCs were the cause of this injury. See In re Paoli R.R. Yard PCB Litig., 916 F.2d 829, 860 (3d Cir. 1990). The e xpert testimony of Alan Todd, who is a certified industri al hygienist, is integral to plaintiff proving the fir st of these elements, and would bolster a medical conclusion on causation by demonstrating that the level of VOCs p resent in the Heller home was significantly higher than the b ackground levels typically present. Without his testimony, dr awn from the tests he performed in the Heller household, Hel ler has adduced no evidence that the Shaw carpet installed in the Heller home emitted VOCs into the air (let alone em itted themat a level sufficient to cause her illness). Furthe r, even if

Todd's testimony is admitted and is sufficient to m eet plaintiff's burden on this first element at the sum mary judgment stage, Dr. Papano's testimony is necessary to prove that Heller became sick. His testimony also is crit ical for proving that the Shaw carpet was the cause of Helle r's illness. While Todd also offered his expert testimo ny regarding the fourth element, i.e., that the VOCs f rom the Shaw carpet caused Heller's illness, as we will dis cuss below, only Dr. Papano is qualified to testify as to this element.6

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5. The Advisory Committee on the Federal Rules of E vidence has proposed changes to Rule 702 that would reflect the standards from Daubert (and Paoli), requiring that an expert' s testimony be based on reliable facts, be the product of reliable principles and methodology, and be based on a reliable applica tion of these principles and methods to the facts of the case. Se e Fed. R. Evid. 702 (Preliminary Draft 1998). 6. We do not focus on the second element, that Hell er inhaled the VOCs. If she is able to prove, through her expe rt witnesses' testimony, that the Shaw carpet installed in the ho me emitted VOCs, that she became ill, and

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A. Dr. Papano

Shaw did not challenge Dr. Papano's qualifications, so we mention them only briefly here. Dr. Papano is board -certified in internal medicine and allergy-immunology. He has been a practicing physician for more than 35 years, and cu rrently treats 60 to 80 patients per week. Dr. Papano has h eld a number of prominent positions at Bryn Mawr Hospital in suburban Philadelphia, and has taught fellows and r esidents in allergy and internal medicine.

Dr. Papano's written expert report, from January 19 97, opines that he "can state with a reasonable degree of medical certainty, that both Mr. and Mrs. Heller's respirat ory problems or difficulties [were] precipitated [by] t he rugs installed in their home in December 1993." Dr. Papa no also testified at the Daubert hearing that, following Mr s. Heller's visit in May 1994, "I concluded that the carpeting in her house was the major factor in her illness." The bas is for Dr. Papano's conclusion was a differential diagnosis dr awn from his examination of Heller, the results of a series of medical tests, review of Heller's personal and family medic al history, and Heller's descriptions of her personal activitie s (smoking, etc.) and environmental conditions ("cats, dogs, th e type of heating system, rugs, pillows, things of that sort" ).Dr. Papano testified that he also relied on the tem poral

relationship between Heller's exposure to the Shaw carpet and the onset of her symptoms, as well as informati on from Todd Environmental Consultants after its testing of the Heller home in April and May 1994. Finally, Dr. Papano rel ied on his more than thirty years of experience treating p atients with allergy-related medical problems and his knowl edge of environmental causes of respiratory problems gained at professional seminars he attended.

___________________________________________________ ____ that the VOCs caused her illness, it certainly woul d be within a jury's purview to find that Heller had inhaled the VOCs, without further direct proof.

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The District Court excluded all of Dr. Papano's tes timony, largely because he could point to no studies indica ting at

what level the VOCs detected in the Heller home cou ld cause symptoms such as those experienced by Mrs. Heller, see Heller, 1997 WL 535163, at *15; his differential di agnosis "failed to rule out all alternative possible causes of Carol Heller's illness," id. at *16; and the court found that the temporal relationship on which Dr. Papano relied wa s weak,

see id. at *17. We address each of these in turn.

1. Lack of Studies

The District Court faulted Dr. Papano for citing "n o research to support his contention that the levels of VOCs detected by Todd Environmental can and did cause th e type of illness allegedly experienced by [Mrs. Heller]." Id. at *15. The court found that the lack of studies supporting Dr. Papano's conclusion was a "defect" in his testimony . Id. We do not believe that the court's reading of Rule 702 --as requiring research studies supporting a finding of general causation--is correct. Assuming that Dr. Papano conducted a thorough differential diagnosis (see infra Part I II.A.2) and had thereby ruled out other possible causes of Hell er's illness, and assuming that he had relied on a valid and strong temporal relationship between the installati on of the carpet and Heller's problems (see infra Part III.A. 3), we do not believe that this would be an insufficiently valid methodology for his reliably concluding that the carpet caused Heller's problems.

A number of courts, including our own, have looked favorably on medical testimony that relies heavily on a temporal relationship between an illness and a caus al event. See, e.g., Zuchowicz v. United States, 140 F.3d 381 , 385 (2d Cir. 1998); Kannankeril v. Terminix Int'l, Inc., 12 8 F.3d 802, 809 (3d Cir. 1997). The temporal relationship will often be(only) one factor, and how much weight it provides for the

overall determination of whether an expert has "goo d grounds" for his or her conclusion will differ depe nding on

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the strength of that relationship. For example, if there was a minor oil spill on the Hudson River on the same day that Heller began experiencing her symptoms in West Ches ter, Pennsylvania, and she recovered around the time the oil was cleaned up, a proper differential diagnosis and tem poral analysis by a well-qualified physician such as Dr. Papano could not possibly lead to the conclusion that the oil spill caused Heller's illness. See, e.g., Paoli, 35 F.3d at 745 (both the methodology and the application of that methodo logy must be reliable). Conversely, "if a person were do used with chemical X and immediately thereafter developed sym ptom Y, the need for published literature showing a correla tion between the two may be lessened." Cavallo v. Star E nter., 892 F. Supp. 756, 774 (E.D. Va. 1995), aff'd in relevan t part, 100 F.3d 1150, 1159 (4th Cir. 1996), cert. denied, 118 S. Ct. 684 (1998).

The present case falls between these two hypothetic als. In this middle area, we do not believe that Daubert an d Paoli require a physician to rely on definitive published studies before concluding that exposure to a particular obj ect or chemical was the most likely cause of a plaintiff's illness. Both a differential diagnosis and a temporal analys is, properly performed, would generally meet the requir ements of Daubert and Paoli. While again emphasizing that the Daubert/Paoli factors are simply guideposts, we not e that differential diagnosis "consists of a testable hypo thesis," has been peer reviewed, contains standards for controll ing its operation, is generally accepted, and is used outsi de of the judicial context. Paoli, 35 F.3d at 742 n.8.

The question we have thus posed is whether the expe rt's

conclusion can be considered reliable if it is base d on these scientifically valid methods, but is not based on p ublished studies. We acknowledge that a number of courts hav e answered this question in the negative. See, e.g., Moore v. Ashland Chem. Inc., 151 F.3d 269, 278 (5th Cir. 199 8) (en banc) (holding that, absent a "compelling" situatio n such as the Cavallo example above, a temporal relationship is to be given little weight when there are few scientific s tudies

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supporting a medical expert's specific causation di agnosis), petition for cert. filed, 67 U.S.L.W. 3409 (U.S. De c. 17, 1998) (No. 98-992); Cavallo, 892 F. Supp. at 766-69 (excl uding expert testimony on causation primarily because "th ere is nosupport for this causation theory in the scientific literature").

But see Kennedy v. Collagen Corp., 161 F.3d 1226, 1 229 (9th Cir. 1998) (finding district court abused its discr etion by excluding expert testimony that was based on reliab le methodology simply because "no epidemiological or a nimal studies" linked defendant's product to plaintiff's disease).

The Supreme Court has held that it was not an abuse of a district court's discretion to exclude expert testi mony when there was "too great an analytical gap between the data [of scientific studies] and the opinion proffered," Joi ner, 118 S. Ct. at 519, but we do not read the Supreme Court as requiring a medical expert to always rely on publis hed studies indicating the exposure necessary to cause a particular illness. Rather, given the tenuous link in Joiner between plaintiff's exposure to PCBs and the onset of his cancer a number of years later, the lack of studies linking PCBs to cancer in humans left only "the ipse dixit of the expert" to support his conclusion. Id. Therefore, t he Court

held that it was not an abuse of discretion for the district court to exclude the expert's testimony. See id.

Given the liberal thrust of the Federal Rules of Ev idence, the flexible nature of the Daubert inquiry, and the proper roles of the judge and the jury in evaluating the u ltimate credibility of an expert's opinion, we do not belie ve that a medical expert must always cite published studies o n general causation in order to reliably conclude that a part icular object caused a particular illness. Cf. McCullock v . H.B. Fuller Co., 61 F.3d 1038, 1043 (2d Cir. 1995) (affirming a dmission of treating doctor's testimony despite the fact tha t he "could not point to a single piece of medical literature t hat says glue fumes cause throat polyps"). To so hold would doom from the

outset all cases in which the state of research on the specific ailment or on the alleged causal agent was in its e arly stages, and would effectively resurrect a Frye-like bright- line

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standard, not by requiring that a methodology be "g enerally accepted," but by excluding expert testimony not ba cked by published (and presumably peer-reviewed) studies. W e have held that the reliability analysis applies to all a spects of an expert's testimony: the methodology, the facts unde rlying the expert's opinion, the link between the facts and th e conclusion, et alia. See Paoli, 35 F.3d at 743-45. However, not only must each stage of the expert's testimony be reliable, but each stage must be evaluated practically and fl exibly without bright-line exclusionary (or inclusionary) rules.

In the actual practice of medicine, physicians do n ot wait for conclusive, or even published and peer-reviewed , studies to make diagnoses to a reasonable degree of medicalcertainty. Such studies of course help them to make various

diagnoses or to rule out prior diagnoses that the s tudies call into question. However, experience with hundreds of patients, discussions with peers, attendance at conferences a nd seminars, detailed review of a patient's family, pe rsonal, and medical histories, and thorough physical examinatio ns are the tools of the trade, and should suffice for the making of a differential diagnosis even in those cases in which peerreviewed studies do not exist to confirm the diagno sis of the physician. The Federal Rules of Evidence recognize as much. See, e.g., Fed. R. Evid. 703 advisory committee's n ote ("[A] physician in his own practice bases his diagnosis o n information from numerous sources and of considerab le variety . . . . The physician makes life-and-death decisions in reliance upon them. His validation, expertly perfor med and subject to cross-examination, ought to suffice for judicial purposes.").

We repeat that all of these reliable methods for ma king a diagnosis cannot sanitize an otherwise untrustworth y conclusion. See Paoli, 35 F.3d at 745-46; see also Joiner, 118 S. Ct. at 519 ("A court may conclude that there is simply too great an analytical gap between the data and the op inion proffered."). In this case, however, there is certa inly evidence

in the record--from Shaw's own records and from rel iable studies--that carpets emit VOCs and that VOCs can c ause

15

certain health problems. This might be sufficient t o give Dr. Papano "good grounds" for making his conclusion, ev en though the District Court (or a jury) may not agree with that conclusion. Therefore, to the extent that the Distr ict Court excluded Dr. Papano's testimony on the basis that i t was not grounded in scientific studies, it erred. However, it was not necessarily error to exclude Dr. Papano's causation

conclusion as unreliable if he relied on no scienti fic studies and the remaining foundation for his conclusion was shaky.

2. Dr. Papano's Differential Diagnosis

The District Court also found it important that Dr. Papano "failed to rule out all alternative possible causes of Carol Heller's illness." Heller, 1997 WL 535163, at *16 ( emphasis added). Applying plenary review, we hold that this is a more stringent standard for a medical expert's different ial diagnosis than is required under Rule 702. A medical expert's

causation conclusion should not be excluded because he or she has failed to rule out every possible alternati ve cause of a plaintiff's illness. As Professor Capra, Reporter to the Advisory Committee on the Federal Rules of Evidence , has put it:[T]o require the experts to rule out categori cally all other

possible causes for an injury would mean that few experts would ever be able to testify . . . .

. . . Obvious alternative causes need to be ruled out. All possible causes, however, cannot be and n eed not be eliminated before an expert's testimony will be admitted.

Daniel J. Capra, The Daubert Puzzle, 32 Ga. L. Rev. 699, 728 (1998).

Differential diagnosis, as we noted in Paoli, is "t he basic method of internal medicine." Paoli, 35 F.3d at 755 . Dr. Papano engaged in this basic method in a reliable m anner, ordering standard laboratory tests, physically exam ining the

16

plaintiff, taking medical histories, and considerin g alternative causes of the plaintiff's illness. See id. at 755, 758. That he used this technique to "testify to a novel conclusi on" is not sufficient grounds for excluding his testimony. Id. at 759 n.27. Dr. Papano was not required to rule out all a lternative possible causes of Heller's illness. Rather, only " where a defendant points to a plausible alternative cause a nd the doctor offers no explanation for why he or she has concluded that was not the sole cause, that doctor's methodol ogy is

unreliable." Id.

When cross-examining Dr. Papano at the Daubert hear ing, Shaw offered a number of plausible alternative caus es, including dust from other carpets, benzene and 2- butoxyethanol from other sources, and paint and new hardwood floors in the house. Dr. Papano did not of fer detailed explanations for why he concluded that the se were not the causes of plaintiff's illness, but his resp onses, grounded in the alleged temporal relationship, the results of Todd's testing showing a reduction in VOCs when the carpet was removed, and Heller's medical history and physi cal examination, certainly are more than "no explanatio n." See, e.g., App. at A602 (Dr. Papano's discussion of his consideration of other possible causes). Had the Di strict Court applied the proper standard for evaluating a differential diagnosis, we might conclude that it had not abused its discretion in finding that Dr. Papano's responses w ere inadequate, but it did err in requiring him to "rul e out all alternative possible causes."

As we concluded in Paoli, a physician need not cond uct every possible test to rule out all possible causes of a patient's illness, "so long as he or she employed s ufficient diagnostic techniques to have good grounds for his or her conclusion." Paoli, 35 F.3d at 761. More recently, we heldthat a district court erred in excluding expert med ical

testimony because a defendant's suggested alternati ve causes (once adequately addressed by plaintiff's expert) a ffect the weight that the jury should give the expert's testi mony and not the admissibility of that testimony. See Kannan keril, 128

17

F.3d at 808. In Kannankeril, we held that even abse nt hard evidence of the level of exposure to the chemical i n question, a medical expert could offer an opinion that the ch emical caused plaintiff's illness. See id. at 809. The med ical expert there relied primarily on the temporal relationship and the nature of the plaintiff's complaints, as in the pre sent case. While the potential harm of the chemical in that ca se was clearer than in this case, there was also some info rmation indicating that there may not have been a harmful l evel of the chemical in Kannankeril's home. Nonetheless, we emp hasized

that the district court should take care not to "mi stake credibility questions for admissibility questions." Id. If the medical expert's "opinion on causation has a factua l basis and supporting scientific theory" that is reliable, it should be

admitted. Id.

3. Temporal Relationship

Neither Heller nor Dr. Papano disputes the absence of definitive studies establishing the level at which the VOCs detected in the Heller home could cause respiratory illnesses such as those Heller experienced. Nor do they dispu te that studies linking Shaw carpeting to such illnesses do not exist. Rather, they rely heavily on the temporal relations hip between the installation of the carpeting and the o nset of Heller's illness, as well as the fact that she appe ared to improve in health when she was away from her home. As we noted in Part III.A.1 supra, we do not believe that the lack of studies linking an alleged defective product to a p laintiff's illness is fatal to a plaintiff's case on causation . However, as noted, some reliable basis for a causation conclusi on must exist--and here, that basis was largely the alleged temporal relationship between the installation (and removal) of the Shaw carpet and the presence of Heller's illness.

The District Court relied on three major weaknesses in the temporal relationship to find Heller's burden to pr ove causation unmet. We review the factual findings of the District Court for clear error and can find none, a s the

18

background facts to its critique of Dr. Papano's te mporal conclusion are undisputed: (1) the Shaw carpeting w as installed in the Heller home in mid-December 1993; (2) CarolHeller first experienced respiratory problems no ea rlier than

late December 1993; (3) Mr. and Mrs. Heller experie nced renewed symptoms upon returning to the home in May 1994, almost a week after the carpet had been removed; an d (4) although Dr. Papano originally relied on the same t emporal relationship to conclude that the carpeting was the cause of Thomas Heller's illness, Mr. Heller actually experi enced his symptoms prior to the installation of the Shaw carp et.

In reaching its legal conclusion regarding the temp oral relationship, the court first noted that Heller did not experience symptoms until at least two weeks after the Shaw carpeting was installed.7 Dr. Papano himself testif ied that a reaction to VOCs in the home would typically occur within 24 hours of exposure to the VOCs. See App. at A638. Wh ile Heller contends that this can be explained by her u se of an upstairs bedroom (rather than the downstairs master bedroom) after the Shaw carpet was first installed, she

admitted that both of these rooms contained the Sha w carpet.

Not only did Heller's symptoms not appear until at least one or two weeks after the Shaw carpeting was insta lled, but they remained after the carpet was removed in May 1 994. The District Court properly faulted Dr. Papano's te stimony for not accounting for this fact as well. Plaintiff att empts to explain this weakness in the temporal relationship by reference to the "sink" effect, by which VOCs sink into objects other than the ones from which they are emitted and then are re-emitted at later times. See Appellants' Br. at 2 1 n.6. This explanation is dubious, however, as the air was act ually

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7. Plaintiff relies on the testimony of her other e xpert, Alan Todd, to establish the level of VOCs at the time th e carpet was installed in mid-December. While we find serious pr oblems with his calculations, see infra Part III.B.2, we note t hat the level of VOCs in mid-December would appear immaterial, as Heller did not experience any adverse reactions until at least one or two weeks later, when, according to plaintiff's own exp erts, the level of VOCs would be substantially lower.

19

measured on the day Heller returned to the home and experienced renewed symptoms--and there were virtua lly no VOCs present at that time. Further, this "sink" eff ect theory was disavowed by Heller's own environmental expert. See App. at A882-883. Most importantly, it is not evide nt that Dr. Papano relied on any "sink" effect or any other exp lanation for why Heller continued to suffer ill effects from the Shaw carpeting after it had been removed from the house. Finally,the District Court noted that Dr. Papano's temporal analysis

failed to explain why Thomas Heller (who Dr. Papano also concluded suffered ill effects from the Shaw carpet ) exhibited allergy symptoms prior to the installation of the S haw carpet.

These weaknesses, according to the District Court, "disprove the existence of a temporal relationship. " Heller, 1997 WL 535163, at *17. While we review such a conc lusion for abuse of discretion, as noted above, our review of the court's legal analysis--i.e., whether it properly f ollowed Rule 702 as prescribed in Daubert and Paoli--is plenary. The court's analysis of the temporal relationship inclu ded the criticism that "plaintiffs proffer no statistical e vidence to show the existence of a statistically significant correl ation" between the Hellers' symptoms and their exposure to the Sha w carpet. Id. However, a physician's diagnosis, based in part on a strong temporal relationship between symptoms and exposure, need not necessarily be supported by "a statistically significant correlation." What is req uired is that the physician have "good grounds" for his or her di agnosis. See Paoli, 35 F.3d at 744 (noting that, even if the judge believes "there are better grounds for some alterna tive

conclusion" and that there are some flaws in the ex pert's methods, if there are "good grounds" for the expert 's conclusion, it should be admitted). Further, when t he temporal relationship is strong and is part of a st andard differential diagnosis, it would fulfill many of th e Daubert/Paoli factors. See id. at 742 n.8.

Here, however, we have no problem concluding that t he temporal relationship between the exposure to the S haw carpeting and the onset of Heller's illness was que stionable

20

at best and exculpatory at worst. While the distric t court may not reject an expert's conclusion simply because th e court finds it wanting, it is surely within the court's p rovince to ensure that the conclusion, particularly a medical expert's ultimate conclusion on causation, "fits" with the d ata alleged to support it. See id. at 746 ("[T]he expert's view that a particular conclusion 'fits' a particular case must itself constitute scientific knowledge . . . ."). Had the Hellers experienced a prompt reaction at the time the Shaw carpeting was installed in mid-December 1993, and had they su ffered no reaction upon return to their home after the Sha w carpet was removed in May 1994, this would be the type of temporal relationship that might reliably support a conclusi on that the carpet was the cause of plaintiff's illness. Howeve r, that is not

the case here.

4. Dr. Papano's Testimony: Summary and ConclusionWe have explained that the District Court erred to the

extent that it required Dr. Papano's testimony to b e backed by scientific studies linking the type and level of VOCs detected in the Heller home to Heller's illness, an d to the extent that it required Dr. Papano to rule out all other possible causes of Heller's illness before concludi ng that the Shaw carpet was the cause. The District Court could

, however, properly consider the fact (rather than re quiring it as a prerequisite to admissibility) that Dr. Papano relied on few, if any, studies linking exposure to the VOCs a llegedly emitted by the Shaw carpet to the illnesses suffere d by Heller. It could also properly consider Dr. Papano's (weak) responses to Shaw's proffered alternative theories on the cau se of Heller's illness in evaluating whether he truly had "good grounds" to arrive at the causation conclusion he r eached.

Dr. Papano relied extremely heavily on the temporal relationship between the installation of the carpet and Heller's illness, and the District Court did not er r in concluding that this relationship was unreliable. W ithout either scientific studies pointing to VOCs of the t ype and

21

amount detected as the culprit or a reliable tempor al relationship, Dr. Papano was left with no valid mea ns for concluding that the Shaw carpet was the cause of He ller's illness. Dr. Papano's conclusion had to "fit" with the data and the methodology that precedes it. See Paoli, 35 F.3 d at 746. Even if the data (e.g., the medical history, the la boratory studies, evidence of VOCs in the Heller home) and t he methodology (i.e., the differential diagnosis) were reliable, the District Court did not err in finding that the conc lusion Dr. Papano reached did not reliably flow from this data and methodology. Under these circumstances, the Distric t Court did not abuse its discretion in ultimately deciding to exclude Dr. Papano's testimony regarding the cause of Helle r's

illness.8

B. Alan Todd

Plaintiff's second expert witness, Alan Todd, of To dd Environmental Consultants, opined in his initial ex pert report that "the illness[es] suffered by the Heller family were caused

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8. We add that the District Court should not necess arily have excluded all of Dr. Papano's testimony. In many cas es, a treating physician whose methods and data are reliable, but whose causation conclusion is excluded as unreliable, may still have other reliable testimony to offer. In such a case, the medicalexpert should be permitted to "testify about his ex amination of

[the plaintiff], the tests he conducted, and the di agnosis he reached," Moore, 151 F.3d at 273, as these are all based on reliable methods. See also Cavallo, 892 F. Supp. at 770 ("There is no question that Dr. Bellanti is qualified to te stify regarding the nature of Ms. Cavallo's illnesses . . . . Rather, the focus of the dispute is whether his opinion reg arding the cause of these illnesses is scientifically valid an d therefore admissible under Daubert." (first emphasis added)). Thus, even if it was proper to exclude Dr. Papano's expert testim ony regarding the cause of Heller's illness, as we conclude it wa s, testimony

as to his examination and treatment of her illness was almost certainly relevant and reliable. It would be releva nt to at least one of the elements in most of Heller's claims, i.e ., whether or not she suffered an injury (as well as the extent o f her injuries, a relevant factor in any damages analysis ). Of course, without Dr. Papano's causation testimony, summary j udgment may

still have been warranted--and we conclude that it was--because

without it there was insufficient evidence of causa tion to get to the jury.

22

by their prolonged exposure to the VOC's measured i n their home and emitted by the carpeting manufactured by S haw

Industries." Todd based his conclusion on his testi ng of the

air in a closet of the Heller home in which the Sha w carpet had been installed, and on his extrapolation from t he results of these closet tests. He thereby estimated the lev el of VOCs emitted by the Shaw carpet at the time it was insta lled, approximately four months prior to his testing. We note preliminarily that we are doubtful that a non-medic al expert such as Todd is qualified to testify as to the caus e of

someone's illness.9 We need not address that issue here, however, because we conclude that the District Cour t did not abuse its discretion in excluding Todd's extrapolat ions as being unreliable so that any arguable basis for Tod d's causation conclusion was missing, making it appropr iate for

the District Court to exclude Todd's causation test imony.

Todd is a certified industrial hygienist, who consu lts on environmental problems in occupational and resident ial settings. His qualifications were not challenged by defendant, though as we discuss below, his methodologies were thoroughly attacked. Because Heller must show that her exposure to VOCs was at a greater level than "the n ormal 'background' level," Paoli, 916 F.2d at 860-61, and that this exposure came from defendant's carpet, see id. at 8 60, Todd's testimony was necessary for her to survive summary judgment. Todd testified that, at the time the Shaw carpet was installed (December 13-14, 1993), the level of benzene in the air in the Heller home was approximately 1712 p arts per billion ("ppb"), and that this benzene came from th e Shawcarpet. He also estimated that, at that time, the l evel of other

VOCs was approximately 11,469 ppb, and that these V OCs

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9. While Todd was knowledgeable about studies on VO Cs and illness, and on recommended maximum occupational VO C levels, he is not a physician and did not examine the Hellers nor discuss with them their symptoms or their medical histories . Thus, whatever his qualifications for testifying about th e source and level of VOCs in the Hellers' house or his expertis e regarding dangerous levels of VOCs, his qualification to offe r an opinion

on the ultimate cause of the Hellers' illnesses is another

matter.

23

came from the Shaw carpet. If his methodologies wer e reliable, and his application of these methodologie s to the facts of the case was reliable, his conclusion that there were VOCs, emitted from Shaw's carpet, at levels higher than background levels could support a proper medical di agnosis that the Shaw carpet caused the plaintiff's illness

.

1. Subtraction Methodology10

Todd's method for determining the source and level of VOCs in the Heller house was to take air samples in a bedroom closet before and after the Shaw carpet had been removed from the house (and the closet). Comparing the two measurements, he determined the amount of VOCs emit ted by the Shaw carpet, the only item present for the f irst test and absent for the second one. If the methodology f or collecting air samples and for measuring the VOCs p resent in the air was valid and reliable, and the difference in the level of VOCs was significant, this part of Todd's testim ony would be probative of whether or not the Shaw carpeting e mitted VOCs, and should have been admitted.

While the District Court faulted Todd's subtraction methodology on a number of counts, we uphold its de cision to exclude this testimony largely because the concl usions Todd reached could not reliably flow from the data and methodology he used. We first consider the District Court's criticisms of Todd's subtraction methodology (not a ll of which we find warranted) before turning to our own critiq ue of his testimony.

The District Court found that the studies cited by Todd for the proposition that carpet such as Shaw's could ca use Heller's illness did not support this conclusion. S ee Heller, 1997 WL 535163, at *9. We address this aspect of th e matter___________________________________________________ ____

10. Although not so labeled by Todd, the parties a nd the

District Court utilized the terms "subtraction meth odology" and "back-extrapolation methodology" to describe Todd's two major methodologies. For the sake of consistency, we will do likewise.

24

in the margin, for, given our ultimate conclusion, we need not decide whether the District Court's analysis of the studies was an appropriate factor in determining whether To dd's subtraction methodology itself was valid and reliab le.11

In addition, although Todd testified that he used a n accepted methodology for collecting the air samples and described this method in detail, Shaw and the Distr ict Court criticized him for not using some other test, speci fically a closed chamber laboratory test. While the latter is an accepted test for measuring compounds in new carpet , it is neither the only nor necessarily the best test for measuring VOCs from carpet already installed in a home. Furth er, the record provides ample evidence that laboratory test s and onsite tests produce similar results, see, e.g., App. at A88, and defendant's own expert conducted on-site tests in a number of carpet-emission studies, see id. at SA0892, SA10 13, SA1030. That expert also admitted using in a prior study essentially the same "subtraction method" used by T odd. See

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11. In our view, the record can be read to support Todd's claim that carpeting such as Shaw's can emit some of the VOCs detected in the Heller home and may cause illnesses similar to those suffered by Heller after prolonged exposure. In any event, we do not believe that unequivocal studies are required b efore a qualified expert may opine that a product emits a c ertain compound or causes a certain irritation, if the bas is for the opinion is otherwise reliable and scientifically va lid.

Further, this aspect of Todd's testimony was based on first-hand, field testing of the object in question--the Shaw c arpet. If Todd was qualified to conduct such tests, and if his mea ns of collecting air samples was scientifically valid and the initial conclusion he drew--that the Shaw carpet was the so urce of a certain level of VOCs--was reliably drawn from the field testing, this testimony would be both reliable and relevant. We note that this is not a case in which a party sought to avoid the application of Daubert by labeling such testing "no n-scientific." See, e.g., Carmichael v. Samyang Tire, Inc., 131 F. 3d 1433, 1435- 36 (11th Cir. 1997) (finding that testimony based o n "skill- orexperience-based observation," rather than on "appl ication of

scientific principles or theories," was not subject to Daubert), cert. granted sub nom. Kumho Tire Co. v. Carmichael , 118 S. Ct. 2339 (1998). Here, plaintiff argued that Todd's tes timony met the requirements of Daubert in that it was reliable and valid.

25

id. at A1152-1157.12 Properly performed, such on-si te tests would appear to meet most of the factors suggested in

Daubert and Paoli.

Finally, the District Court placed great weight on Todd's alleged failure to "insure that other variables did not [affect] the air sampling tests." Heller, 1997 WL 535163, at *12. However, Todd testified that the contents of the cl oset (and the house) remained constant and that the environme ntal conditions in the house were essentially static (i. e., no persons came or went, the windows were not opened, the rate of air flow was not changed, etc.). While it is tru e that the concentration of VOCs is affected by more than the emission from a source such as carpeting, a substantial decl ine in the amount of VOCs would constitute strong (and reliabl e)

evidence that at least some of these VOCs were comi ng from the Shaw carpet--the only item that was removed bef ore the lower readings were taken.

Our decision does not turn, however, on the validit y of Todd's air sampling methodology, i.e., on whether t he testing

was unreliable because he did not conduct different tests or did not control for other possible sources of VOCs. This is because the District Court was correct to question the reliability of Todd's conclusions. The level of VOC s detected by Todd's closet tests, even if they could all be a ttributed to the Shaw carpet, were substantially lower than any amounts

ever known or believed to cause illnesses in humans ; in fact,

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12. The court also faulted Todd's testimony becaus e he "did not conduct further tests to ascertain whether changes in the levels

of VOCs were attributable to the removal of the car pet or whether the changes were attributable to the natural fluctu ation in VOC levels within the home." Heller, 1997 WL 535163, at *12. It is

not clear what "further tests" the District Court w ould have required. Todd did not take snapshot tests at singl e moments, which would have been subject to natural fluctuatio ns and random error; such tests likely would not be reliable enou gh to meet the Daubert standard. Rather, Todd took air sample readings over eight hours on one day, with the carpet present, an d then took readings for eight hours on a second day, without t he carpetpresent. Such prolonged readings may be sufficient to account for

"natural fluctuations in VOC levels."

26

they appear to be extremely close to the background amounts (i.e., the levels naturally occurring in the air) f or each of the VOCs.13 A number of studies cited by the parties an d contained in the record have concluded that any ill effects from these particular VOCs (and related ones) only occur at much higher levels than those found in the Heller h ome. See, e.g., App. at SA0835-0840 (finding basic irritation at 50-750 ppb of VOCs; headaches at 750-6250 ppb; and additio nal neurotoxic effects at levels above 6250 ppb); id. a t A126 (reporting pulmonary irritation at 275 ppb; slight sensory irritation at 600 ppb); id. at SA0210 (finding that persons exposed to 25,000 ppb of benzene for eight hours demonstrated no acute effect). Another major study found that the background levels of benzene averaged 5 pp b overall and about 3 ppb indoors, see id. at SA0200, actuall y above the levels (2.2 ppb) detected in the Heller home in April, when the Shaw carpet was still in the house.14

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13. We note that a number of the VOCs allegedly att ributable to the Shaw carpet were detected at levels well below the maximum amounts recommended by various federal agencies and professional groups. For example, only 2.22 ppb of benzene was d etected in April 1994; the lowest suggested limit for exposure to benzene is 500 ppb. Other VOCs detected in the closet, with th e maximum amount attributable to the Shaw carpet and the lowe st recommended limit, include:

VOC Amount Found Recommen ded (in ppb) Limit (i n ppb)

2-Butoxyethanol 5.60 20,000 Carbon Tetrachloride 0.13 2,000 Cumene 0.11 50,000 Methyl Chloroform 0.09 200,000

See Richard J. Lewis, Sr., Hazardous Chemicals Desk Reference 113, 180, 235, 318, 745 (4th ed. 1997). We note tha t these limits are for long-term occupational exposure and assume exposure at these levels for 40 hours per week, indefinitely.

14. Unfortunately, comparing these studies and ind ustry documents to Todd's findings can be difficult, as t he latter are reported in terms of ppb (parts per billion), while many of the studies and industry documents measure air concentr ation in mg/m3 (milligrams per cubic meter) or ug/m3 (micrograms p er cubicmeter). The conversion from one to the other is

27

Todd attempted to address this shortcoming in his testimony by dividing the suggested occupational li mits by 420, based on two assumptions whose validity is pro blematic. First, because the limits are based on a 40-hour wo rk week and there are potentially 168 hours per week in whi ch a person could occupy her home (if she never left), T odd reduced the limits by 4.2. Then, because the occupa tional limits are based on an average healthy adult, Todd testified that it is standard practice to reduce these limits further by a factor of 100, to account for the fact that homes include children, older adults, unhealthy persons, etc. As a result, he opined that the limit for exposure to benzene in th e home is actually approximately 1.2 ppb (i.e., 500 ppb / 420 ), slightly lower than the amount attributable to the Shaw carp et.

This methodology is suspect. In one study in the re cord, the American Society of Heating, Refrigeration, and Air Conditioning Engineers ("ASHRAE") is cited as recom mending a maximum level of contaminants arrived at by divid ing the OSHA limit by 10, see App. at SA0860-0861, for esse ntially the same reason that Todd gave for dividing the per missible limits by 420. The OSHA limit for benzene is 1000 p pb; the ASHRAE limit, then, would be 100 ppb, still well ab ove the amount detected in the Heller home in April (2.22 p pb). The OSHA limit for 2-butoxyethanol is 25,000 ppb, makin g the ASHRAE limit 2500 ppb, significantly higher than th e amount detected in the Hellers' house (5.60 ppb). A t all events, even if the methodology is valid, the level s measured in April (the earliest period at which Todd actuall y took air concentration measurements) do not even approach th e (modified) recommended maximums for any of the othe r

VOCs.

Thus, while the closet tests conducted by Todd were not necessarily unreliable, because the level of VOCs d etected

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different for every compound. For benzene, it is ab out 3 ug/m3 for every 1 ppb; for other compounds, it ranges from about 3 ug/m3 for every 1 ppb to 7 ug/m3 for every 1 ppb. For the sake of analyzi ng Todd's testimony, we have made rough conversions, using 4 ug/m3 for every 1 ppb. No difference in outcome would result from using another conversion equation.

28

and (arguably) attributable to the Shaw carpet were so lowand so close to background levels, the District Cou rt did not

abuse its discretion in excluding Todd's testimony that the Shaw carpet was emitting VOCs sufficient to cause H eller's

illness--a conclusion that was unreliable if based on the closet tests alone. Todd, however, attempted to rei nforce his closet tests--and to provide a stronger foundation for his opinion about the dangerous level of VOCs in the ho use--by introducing his back-extrapolation methodology in a supplemental expert witness report (issued in March 1997, following his original January 1997 report). We tur n to this aspect of his testimony.

2. Back-Extrapolation Methodology

If Todd's sampling of the air in the closet: (1) wa s reliable and adequately controlled for factors other than th e Shaw carpet, and (2) demonstrated that the Shaw carpet w as emitting VOCs at potentially harmful levels, his te stimony would be sufficiently reliable to meet the Daubert standard

and hence would be admissible. While we believe tha t the first proposition may be true, as noted above, the closet tests

themselves fail to demonstrate the second. If it wa s possible to use the results of the closet tests to estimate, in a scientifically valid way, the level of VOCs emitted by the carpet at some earlier time, and if these estimated levels were potentially harmful, again, Todd's testimony would be reliable and relevant. We express no opinion as to whether extrapolation back in time, using known levels of c ompounds and a scientifically valid mathematical formula for the extrapolation, would meet the standards of Rule 702 and Daubert. Cf. Ruiz-Troche v. Pepsi Cola of P.R. Bott ling Co., 161 F.3d 77, 85 (1st Cir. 1998) (approving of a back-ex trapolation and half-life methodology that "has been subjected to, and survived, the rigors of testing, publication, and p eer review, and . . . appears to have won significant (if not u niversal) acceptance within the scientific community"). Here, however, it is clear that Todd's formula for his extrapolati on was based

29

on speculation and estimation that was subject to g ross error, and that the District Court did not abuse it s discretionin excluding Todd's testimony based on the backextrapolation.15 Indeed, we doubt that Todd's backextrapolation methodology would meet even one of th e eight suggested factors from Daubert and Paoli.

Heller argues that the back-extrapolation method is "a standard reversibility of chemical processes equati on," Appellants' Br. at 27, but provides no support for the reliability of Todd's equation or for the suggested relationship

between chemical half-lives and the level of VOCs i n the air. Todd's back-extrapolation method relies on at least threequestionable assumptions: (1) the concentration of VOCs in

the air declines exponentially by half-lives (i.e., the level of VOCs are cut in half every X days or weeks or years ); (2) the

half-life of VOCs in the air can be estimated based on information on the decay curve of VOC emissions fro m carpets; and (3) the concentration of VOCs in the a ir is not affected by anything other than its natural half-li fe decline.

None of these assumptions, however, appears support ed by reliable scientific methods or the reliable applica tion of any valid theory. In fact, Todd admitted as much in his own testimony and expert report. See, e.g., App. at A35 0-351, A761-762; id. at SA0247 (Todd's Expert Report: "The precise magnitude of difference quantitatively in off-gassi ng emissions at the carpet between April 1994 and Dece mber 1993 is not readily evident from the published lite rature and or studies conducted by the rug manufacturers or th eir trade associations."). In fact, numerous published studie s and industry documents consistently demonstrate that th e actual rate of decline of emissions from carpet is nothing like a half-

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15. Plaintiff relies heavily on a Louisiana state case to support Todd's back-extrapolation theory. See Appel lants' Br. at 38-40. The judgment in that case, however, has been reversed and a new trial ordered, specifically because the trial court failed to hold a Daubert hearing and to find whether the D aubert criteria were met, as required by Louisiana law. Se e Caubarreaux v. E.I. duPont de Nemours, 714 So. 2d 67, 71-72 (La . Ct. App. 1998).

30

life progression. See, e.g., id. at A128, A145, A24 2, A248-250, A268-270, SA0860, SA0956, SA1020. Rather, emissions decline rapidly in the first hours and days after i nstallation, reaching a level of about 10% of the original emiss ion rate in only one week and as low as .05% of the initial emi ssion rate in only one month. The differences between the emis sion

rates indicated in these studies and those estimate d by Todd's back-extrapolation theory are fairly substan tial. (We express them graphically in the margin.16) For ex ample, under Todd's theory, about ten days after installat ion of new carpet, VOCs would remain at levels approximately 5 0% of their initial level, while the studies in the recor d indicate that the levels would actually be less than 10% of their initial level. Within three weeks of installation, under To dd's theory,

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1631

VOCs would be at 25% of their initial level, while the studies show that carpet, at this point, is emitting only a bout 1% of

the initial amount of VOCs emitted at the time of i nstallation. In short, the VOC levels estimated by Todd greatly exceed those which more likely existed, and follow a very different curve. Therefore, the District Court properly exerc ised its discretion to exclude this part of Todd's testimony

.

Heller contends that even if Todd's "calculations w ere imprecise, it is undisputed that the level of VOC e missions in December 1993 were significantly higher than the VO C levels measured in April 1994." Appellants' Br. at 10 n.2. The problem with this argument, however, is that even i f the levels were higher in December 1993, the calculatio ns of plaintiff's expert were "imprecise" because his met hodology was unreliable, and therefore Heller has presented no reliable evidence to demonstrate what the actual (or even re liably estimated) level of VOCs was in December 1993. With out a reliable method to determine how much higher the le vels were in December 1993, only the actually measured l evels in April 1994 are admissible evidence--and, as noted a bove, these levels were far too low to prove that the Sha w carpet was emitting harmful levels of VOCs.

There are other flaws in Todd's back-extrapolation testimony that also support the District Court's de cision to exclude this testimony. First, Todd conflates emiss ion rates and air concentration rates in his analysis. All of the record

data on which Todd claims he relied to estimate his backextrapolation formula involve the declining emissio n rate:

VOCs are emitted at a certain rate at the time of c arpet installation; by 24 hours later, they are emitted a t approximately half this rate; by a week later, they are emitted at approximately 10% the original rate, etc. The ai r concentration of VOCs (which is what Todd measured in the closet in April and May 1994, and used as the start ing point for his back-extrapolation) is a function of not on ly the rate at which VOCs are emitted from the carpet to the ai r, but also such factors as the rate at which VOCs dissipa te in the air, the size of the room or house in which the VOC s are

32

emitted, the molecular weight of the particular VOC , the rate of air flow, the moisture, light, and air temperatu re in the room, and other factors. See, e.g., John C. Little et al., Modeling Emissions of Volatile Organic Compounds fr om New Carpets, 28 Atmospheric Env't 227 (1994) (describin gdevelopment of a model indicating that air concentr ation of

a VOC is a function of time, distance from carpet, diffusion rate of the VOC, carpet thickness, air flow rate, c arpet and room area, and air volume). Therefore, to measure t he air concentration at one point in time (as Todd did) an d to attempt to estimate the air concentration four mont hs earlier, one would need to know (or have a good estimate of) each of these factors, i.e., emission rates, room size, air flow, dissipation rate of each compound, etc.--none of wh ich Todd considered in his back-extrapolation formula.

Second, there is at least one study in the record t hat appears to indicate that while emission rates of VO Cs decline rapidly (see supra note 16), air concentration leve ls remain fairly constant after an initial slight increase, m aking Todd's conflation of these two factors even more problemat ic. See Alfred T. Hodgson et al., Emissions of Volatile Org anic Compounds from New Carpets Measured in a Large-Scal e Environmental Chamber, J. Air & Waste Mgmt. Ass'n, Mar. 1993, at 316, 323 (describing study indicating that emission rates of styrene and 4-phenylcyclohexene decline ra pidly,

while air concentration rates fluctuate within a re latively narrow range). Therefore, it is entirely plausible that the level of VOCs in the air was not much higher in December 1993 than the very low level measured in April 1994, the only time such VOCs were actually measured.

Finally, if one were to credit Todd's back-extrapol ation theory, it would actually invalidate his closet stu dies, thereby eliminating the only basis for his opinion that the Shaw carpet was the source of the VOCs in the Heller home. This is because the decline in benzene and 2-butoxyethan ol, two of the key VOCs on which plaintiff rests her case, could be explained almost entirely by the back-extrapolation theory, eliminating the possibility that it was the removal of the

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carpet that caused the levels of these VOCs to decl ine. Under Todd's back-extrapolation theory, the benzene would be expected to decline from 2.22 ppb on April 14, 1994 , to approximately 0.40 ppb on May 11, 1994, even withou t the removal of the Shaw carpet; it actually declined to only 0.55 ppb. The 2-butoxyethanol would have been expected t o decline from 5.6 ppb to approximately 1.0 ppb; it a ctually declined to 0.0 ppb, making the maximum amount attributable to the removed carpet only 1.0 ppb-- substantially lower than the recommended limit of 2 0,000 ppb for this compound. The District Court noted thi s inconsistency, see Heller, 1997 WL 535163, at *12, as did Todd himself implicitly on cross-examination at the Daubert hearing, see App. at A543, A886.3. Todd's Testimony: Summary and Conclusion

Although we believe that the District Court may hav e been overly critical of Todd's closet tests and that tho se aspects of its unreliability finding may have been inconsisten t with the exercise of sound discretion, given the patent unre liability of Todd's back-extrapolation theory and the fact that the closet tests did not indicate levels of VOCs anywhere near the levels found to cause illnesses in humans, we hold that th e District Court did not abuse its discretion in excluding all of Todd's testimony. Cf. Paoli, 35 F.3d at 749 n.19 (noting t hat all of an expert's testimony could be excluded as irrelevant if it no longer assists plaintiff's case after certain parts are excluded as unreliable).

IV. Summary Judgment

Without Dr. Papano's testimony on specific causatio n or Todd's testimony on the allegedly higher levels of VOCs in December 1993 (both of which we hold the District C ourt was correct to exclude), the remaining expert testimony and other

evidence in the record are insufficient to create a material

issue on causation. We note that the District Court granted

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summary judgment at least in part because "defendan t's carpeting is not the obvious cause of plaintiffs' i llnesses." Heller, 1997 WL 535163, at *18. This appears to pla ce a more stringent burden on plaintiff than is warranted at summary judgment, but the District Court also relied on the total lack of causation evidence absent the expert testimony, which is a proper ground for summary judgment.

Certain of plaintiff's claims do not rely on the ca usal

connection between Heller's illness and the Shaw ca rpet to survive. However, without Todd's testimony, plainti ff has failed to offer admissible proof that the Shaw carp et was defective. The only claim that does not require pro of of either the causal connection or defectiveness is plaintiff 's misrepresentation claim. We are satisfied, however, that the District Court properly granted summary judgment on this claim as well. See id. at *19 ("[T]here is no evide nce of record to support plaintiffs' assertion that they were inj ured by reliance on [Shaw's] alleged misrepresentation.").

The order of the District Court granting summary ju dgment

to Shaw will be affirmed.

A True Copy:

Teste:

Clerk of the United States Court of Appeals

for the Third Circuit35