1999 Decisions

Opinions of the United

States Court of Appeals

for the Third Circuit

2-3-1999

Heller v. Shaw Ind Inc

Precedential or Non-Precedential:

Docket 97-1735

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Recommended Citation

"Heller v. Shaw Ind Inc" (1999). 1999 Decisions. Paper 30.

http://digitalcommons.law.villanova.edu/thirdcircuit_1999/30
Filed 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 and 

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, ESQUIRE 
 Kent & 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 

_______________ 

OPINION OF THE COURT 

_______________ 

BECKER, Chief Judge: 

This is an appeal by plaintiff Carol Heller ("Heller"), 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 largely a 

function of its exclusion, following an extensive in limine 

hearing, of key expert testimony by which Heller hoped to 

establish liability. See Heller v. Shaw Indus., Inc., No. 

Civ.A.95-7657, 1997 WL 535163 (E.D. Pa. Aug. 18, 1997). In 

reviewing the District Court's rulings, we revisit the caselaw 

interpreting Federal Rule of Evidence 702, particularly 

Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 

(1993), and In re Paoli Railroad Yard PCB Litigation, 35 F.3d 

717 (3d Cir. 1994), and apply their teachings to this case. 

2 

After careful but deferential review, see General Elec. Co. v. 

Joiner, 118 S. Ct. 512, 517 (1997), we conclude that, 

although the District Court erred in excluding certain aspects 

of the experts' proffered testimony, it properly excluded the 

central portions of their testimony, depriving Heller's claim of 

its needed evidentiary support. 

More specifically, the District Court was too restrictive in 

requiring Heller's medical expert to rely on published studies 

specifically linking Heller's illness with Shaw's product, and 

in requiring Heller's medical expert to rule out all alternative 

possible causes of her illness. However, it properly excluded 

this expert's causation testimony because his conclusion 

regarding the cause of Heller's illness was heavily based on 

a flawed temporal relationship between the installation of the 
Shaw carpet and the presence of Heller's illness. The District 

Court also properly excluded the testimony of Heller's 

environmental expert on the grounds that his environmental 

testing revealed levels of dangerous compounds in the air in 

Heller's home that were not significantly higher than 

background levels, and his methodology for extrapolating 

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 necessary 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, Thomas Heller 

experienced allergy symptoms. In November and December 

1993, an allergist advised Mr. Heller to replace the carpeting 

in the home because cat hair from previous owners might 

have caused his allergic reactions. On December 13 and 14, 

1993, the Hellers put new carpeting--manufactured by Shaw 

Industries--in certain rooms of their home, including the 

3 

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

second floor. 

In late December 1993, Carol Heller began to experience 

respiratory problems, including asthma, breathing difficulty, 

wheezing, coughing, and dizziness. After seeking treatment 

from her father, a physician, Heller consulted Dr. Joseph 

Papano, an allergist and one of her two expert witnesses.1 Her 

first visit to Dr. Papano was on February 15, 1994. Dr. 

Papano took Heller's medical and family history, questioned 

her about her environment (whether there were cats or dogs 

in the home, etc.), and performed allergy tests, chest X-rays, 

and pulmonary function tests. Based on the history, tests, 

and a physical examination, Dr. Papano ruled out various 

possible causes of her respiratory problems. In February 

1994, the doctor recommended that Heller contact Alan Todd 

of Todd Environmental Consultants (collectively "Todd") to 

test both the air quality in her home and the carpet.2 When 

Dr. Papano next saw Heller, on March 19, 1994, she was still 

experiencing problems, but informed him that her symptoms 

_______________________________________________________ 

1. Because, as discussed below, Dr. Papano relied heavily for 

his diagnosis on the temporal relationship between the 
installation of the Shaw carpet and the onset of Heller's 

illness, the date on which she began to experience her symptoms 

is a contested and important issue. Dr. Papano originally 

testified at his deposition that her symptoms began in "January 

1994," and he so stated in his expert witness report. 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 January 1994, 

while her father testified that they began either in mid-December 

or during the first two weeks of December. Given the conflicting 

testimony, we find no clear error in the District Court's 

reliance, in its findings following the Daubert hearing, 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 referred Heller 

to Todd at her March 1994 visit, while Todd's expert report 

states that he was first contacted by Heller and did 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 February 1994, 

Dr. Papano must have referred the Hellers to Todd in February. 

4 

improved when she was out of her house. At this time, she 

brought the doctor a sample of the Shaw carpet, which he 

testified had a strong odor. 

The Hellers contracted with Todd to perform the testing of 

the environment in the house and of the carpet. Todd initially 

tested for excessive levels of dust or other possible 

contaminants, finding nothing unusual. By April 7, 1994, the 

Heller family had moved out of their home in an attempt to 

eliminate Heller's respiratory problems. On April 14, 1994, 

Todd tested the air in the closet of one of the Hellers' 

bedrooms; the closet contained both some of the Shaw carpet 

and some carpet from an unknown manufacturer. Todd's 

initial test, conducted over approximately eight hours, 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 closet for 

eight hours. During the period between the two tests, no 

other changes were made in the house: no objects were added 

or removed, the windows remained closed, and no persons 

entered or left the by-now empty house. In the second 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 completely 

disappeared and one (benzene) remained present, but at 
lower levels. Todd's initial conclusion, in a May 23, 1994, 

letter to Heller, was that "none of the compounds identified 

would be expected to typically result in asthmatic or 

sensitization responses." (Later, however, in his first expert 

witness report, dated January 16, 1997, he opined that the 

compounds that disappeared or diminished were emitted 

from the Shaw carpet, and were "the likely source of [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 earlier and 

the May 11 testing would reveal the presence of very few 

5 

VOCs, Mrs. Heller again experienced "wheezing, shortness of 

breath and an irritated throat." The Hellers then left the 

house, never to return. In November 1994, they sold the 

home for less than they had paid for it a year earlier. 

Dr. Papano's expert report stated that he performed a 

differential diagnosis, which involved ruling out possible 

causes of Heller's symptoms other than Shaw's carpet 

(including "an infectious cause"), and, based largely 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 (in his 

original expert report) that "to a reasonable degree of 

scientific certainty, . . . the illness[es] suffered by the Heller 

family were caused by their prolonged exposure to the VOC's 

measured in their home and emitted by the carpeting

manufactured by Shaw Industries." 

In December 1995, the Hellers brought a diversity action 

against Shaw in the District Court for the Eastern District of 

Pennsylvania, under 28 U.S.C. S 1332, alleging breach of 

warranty, failure to warn, negligent and intentional 

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 product 

caused her injuries. Causation therefore was the primary 

focus of the District Court's inquiry and the primary disputed 

issue in this case. 

Following extensive discovery, Shaw moved for summary 

judgment and, as an adjunct to that motion, moved in 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, granting 
defendant's motions for exclusion of plaintiff's expert 

testimony and for summary judgment. See Heller v. Shaw 

6 

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 Joiner, 118 S. 

Ct. at 517. The District Court's interpretation of the 

requirements of Rule 702, however, is subject to plenary 

review. See Paoli, 35 F.3d at 749. As to the District Court's 

entry of summary judgment for defendants, "we exercise 

plenary review, construing all evidence and resolving all 

doubts raised by affidavits, depositions, answers to 

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 determine that 

the District Court properly excluded all of plaintiff's expert 

testimony, summary judgment for defendant was the proper 

course for the key claims of design defect and failure to warn. 

This is because, without either Dr. Papano's or Alan Todd's 

testimony, Heller would be left without any proof of 

causation, a necessary element for each of these claims. 

However, if we decide (as we do) that some of the testimony 

should have been admitted, we must determine whether 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 expert witness 

testimony, on which the causation issue hinges. While there 

are other issues in the case, including breach of warranty 

and misrepresentations, we will address these only briefly, for 

they are easily disposed of without extended discussion. 

II. Expert Witnesses: The Legal Background 

Rule 702 provides: "If scientific, technical, or other 

specialized knowledge will assist the trier of fact to 

understand the evidence or to determine a fact in issue, a 

witness qualified as an expert . . . may testify thereto in the 

form of an opinion or otherwise." Relying on the language of 

7 

Rule 702 and the liberal thrust of the Federal Rules of 

Evidence, the Supreme Court held in Daubert that expert 

testimony need be based only on a reliable and scientifically 

valid methodology that fits with the facts of a case. See 

Daubert, 509 U.S. at 592-93.3 The Court listed four factors to 

guide a district court in its preliminary assessment of these 
requirements, but cautioned that these were guideposts and 

not required factors in each case. The factors are: (1) whether 

the methodology can and has been tested; (2) whether the 

technique has been subjected to peer review and publication; 

(3) the known or potential rate of error of the methodology; 

and (4) whether the technique has been generally accepted 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 are simply 

useful signposts, not dispositive hurdles that a party must 

overcome in order to have expert testimony admitted. In this 

regard, a party seeking to exclude (or to admit) expert 

testimony must do more than enumerate the factors from 

Daubert (and the additional ones from Paoli, discussed below) 

and tally the number that are or are not met by a particular 

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 traditional and 

appropriate means of attacking shaky but admissible

evidence," and that, even if expert testimony is admitted, 

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 the 

Daubert standard yet is "shaky," and cases in which

_______________________________________________________ 

3. In Daubert, the Supreme Court interred the decades-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 the expert's 

testimony could be admitted. See Daubert, 509 U.S. at 588-89. 

8 

admissible expert testimony provides only a "scintilla" of 

support for a claim or defense. Put differently, an expert 

opinion must be based on reliable methodology and must 

reliably flow from that methodology and the facts at issue-- 

but it need not be so persuasive as to meet a party's burden 

of proof or even necessarily its burden of production. 

In Paoli, filed barely a year after Daubert, we identified 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 the technique 
to methods which have been established to be reliable"; (3) 

the expert witness's qualifications; and (4) "the non-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 judge believes 

"there are better grounds for some alternative conclusion," 

and that there are some flaws in the scientist's methods, if 

there are "good grounds" for the expert's conclusion, 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 conclusion was 

"novel" if the methodology and the application of the 

methodology were reliable. See id. at 746 n.15. However, we 

rejected the plaintiffs' argument in Paoli (also urged strongly 

by the plaintiff here) that the district court had abused its 

discretion by examining the experts' conclusions. While "[t]he 

focus, of course, must be solely on principles and 

methodology, not on the conclusions that they generate," 

Daubert, 509 U.S. at 595, a district court must examine the 

expert's conclusions in order to determine whether they could 

_______________________________________________________ 

4. In addition to the "good grounds" requirement, in a diversity 

case such as this, state rules on the degree of certainty 

required of an expert's opinion apply. In Pennsylvania, a doctor 

can give an opinion on the cause of a plaintiff's illness if he 

or she can do so with a reasonable degree of medical certainty. 

See Paoli, 35 F.3d at 750-52. 

9 

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 her prima 

facie case, that Shaw's carpet emitted VOCs into the 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 expert 

testimony of Alan Todd, who is a certified industrial 

hygienist, is integral to plaintiff proving the first of these 

elements, and would bolster a medical conclusion on

causation by demonstrating that the level of VOCs present in 

the Heller home was significantly higher than the background 

levels typically present. Without his testimony, drawn from 

the tests he performed in the Heller household, Heller has 

adduced no evidence that the Shaw carpet installed in the 

Heller home emitted VOCs into the air (let alone emitted them 
at a level sufficient to cause her illness). Further, even if 

Todd's testimony is admitted and is sufficient to meet 

plaintiff's burden on this first element at the summary 

judgment stage, Dr. Papano's testimony is necessary to prove 

that Heller became sick. His testimony also is critical for 

proving that the Shaw carpet was the cause of Heller's 

illness. While Todd also offered his expert testimony 

regarding the fourth element, i.e., that the VOCs from the 

Shaw carpet caused Heller's illness, as we will discuss below, 

only Dr. Papano is qualified to testify as to this element.6 

_______________________________________________________ 

5. The Advisory Committee on the Federal Rules of Evidence 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 application of these 

principles and methods to the facts of the case. See Fed. R. 

Evid. 702 (Preliminary Draft 1998). 

6. We do not focus on the second element, that Heller inhaled 

the VOCs. If she is able to prove, through her expert witnesses' 

testimony, that the Shaw carpet installed in the home emitted 

VOCs, that she became ill, and 

10 

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 currently 

treats 60 to 80 patients per week. Dr. Papano has held a 

number of prominent positions at Bryn Mawr Hospital in 

suburban Philadelphia, and has taught fellows and residents 

in allergy and internal medicine. 

Dr. Papano's written expert report, from January 1997, 

opines that he "can state with a reasonable degree of medical 

certainty, that both Mr. and Mrs. Heller's respiratory 

problems or difficulties [were] precipitated [by] the rugs 

installed in their home in December 1993." Dr. Papano also 

testified at the Daubert hearing that, following Mrs. Heller's 

visit in May 1994, "I concluded that the carpeting in her 

house was the major factor in her illness." The basis for Dr. 

Papano's conclusion was a differential diagnosis drawn from 

his examination of Heller, the results of a series of medical 

tests, review of Heller's personal and family medical history, 

and Heller's descriptions of her personal activities (smoking, 

etc.) and environmental conditions ("cats, dogs, the type of 

heating system, rugs, pillows, things of that sort"). 
Dr. Papano testified that he also relied on the temporal 

relationship between Heller's exposure to the Shaw carpet 

and the onset of her symptoms, as well as information from 

Todd Environmental Consultants after its testing of the Heller 

home in April and May 1994. Finally, Dr. Papano relied on 

his more than thirty years of experience treating patients 

with allergy-related medical problems and his knowledge of 

environmental causes of respiratory problems gained at 

professional seminars he attended. 

_______________________________________________________ 

that the VOCs caused her illness, it certainly would be within a 

jury's purview to find that Heller had inhaled the VOCs, without 

further direct proof. 

11 

The District Court excluded all of Dr. Papano's testimony, 

largely because he could point to no studies indicating at 

what level the VOCs detected in the Heller home could cause 

symptoms such as those experienced by Mrs. Heller, see 

Heller, 1997 WL 535163, at *15; his differential diagnosis 

"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 was weak, 

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

1. Lack of Studies 

The District Court faulted Dr. Papano for citing "no 

research to support his contention that the levels of VOCs 

detected by Todd Environmental can and did cause the 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 III.A.2) and 

had thereby ruled out other possible causes of Heller's 

illness, and assuming that he had relied on a valid and 

strong temporal relationship between the installation 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 causal event. 

See, e.g., Zuchowicz v. United States, 140 F.3d 381, 385 (2d 

Cir. 1998); Kannankeril v. Terminix Int'l, Inc., 128 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 "good 

grounds" for his or her conclusion will differ depending on 

12 

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 Chester, 

Pennsylvania, and she recovered around the time the oil was 

cleaned up, a proper differential diagnosis and temporal 

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 methodology 

must be reliable). Conversely, "if a person were doused with 

chemical X and immediately thereafter developed symptom Y, 

the need for published literature showing a correlation 

between the two may be lessened." Cavallo v. Star Enter., 892 

F. Supp. 756, 774 (E.D. Va. 1995), aff'd in relevant part, 100 

F.3d 1150, 1159 (4th Cir. 1996), cert. denied, 118 S. Ct. 684 

(1998). 

The present case falls between these two hypotheticals. In 

this middle area, we do not believe that Daubert and Paoli 

require a physician to rely on definitive published studies 

before concluding that exposure to a particular object or 

chemical was the most likely cause of a plaintiff's illness. 

Both a differential diagnosis and a temporal analysis, 

properly performed, would generally meet the requirements 

of Daubert and Paoli. While again emphasizing that the 

Daubert/Paoli factors are simply guideposts, we note that 

differential diagnosis "consists of a testable hypothesis," has 

been peer reviewed, contains standards for controlling its 

operation, is generally accepted, and is used outside of the 

judicial context. Paoli, 35 F.3d at 742 n.8. 

The question we have thus posed is whether the expert's 

conclusion can be considered reliable if it is based on these 

scientifically valid methods, but is not based on published 

studies. We acknowledge that a number of courts have 

answered this question in the negative. See, e.g., Moore v. 

Ashland Chem. Inc., 151 F.3d 269, 278 (5th Cir. 1998) (en 

banc) (holding that, absent a "compelling" situation such as 

the Cavallo example above, a temporal relationship is to be 

given little weight when there are few scientific studies 

13 

supporting a medical expert's specific causation diagnosis), 

petition for cert. filed, 67 U.S.L.W. 3409 (U.S. Dec. 17, 1998) 

(No. 98-992); Cavallo, 892 F. Supp. at 766-69 (excluding 

expert testimony on causation primarily because "there is no 
support for this causation theory in the scientific literature"). 

But see Kennedy v. Collagen Corp., 161 F.3d 1226, 1229 (9th 

Cir. 1998) (finding district court abused its discretion by 

excluding expert testimony that was based on reliable 

methodology simply because "no epidemiological or animal 

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 testimony when 

there was "too great an analytical gap between the data [of 

scientific studies] and the opinion proffered," Joiner, 118 S. 

Ct. at 519, but we do not read the Supreme Court as

requiring a medical expert to always rely on published 

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, the 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 Evidence, 

the flexible nature of the Daubert inquiry, and the proper 

roles of the judge and the jury in evaluating the ultimate 

credibility of an expert's opinion, we do not believe that a 

medical expert must always cite published studies on general 

causation in order to reliably conclude that a particular 

object caused a particular illness. Cf. McCullock v. H.B. Fuller 

Co., 61 F.3d 1038, 1043 (2d Cir. 1995) (affirming admission 

of treating doctor's testimony despite the fact that he "could 

not point to a single piece of medical literature that 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 early stages, 

and would effectively resurrect a Frye-like bright-line 

14 

standard, not by requiring that a methodology be "generally 

accepted," but by excluding expert testimony not backed by 

published (and presumably peer-reviewed) studies. We have 

held that the reliability analysis applies to all aspects of an 

expert's testimony: the methodology, the facts underlying the 

expert's opinion, the link between the facts and the 

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 flexibly 

without bright-line exclusionary (or inclusionary) rules. 

In the actual practice of medicine, physicians do not wait 

for conclusive, or even published and peer-reviewed, studies 

to make diagnoses to a reasonable degree of medical
certainty. Such studies of course help them to make various 

diagnoses or to rule out prior diagnoses that the studies call 

into question. However, experience with hundreds of patients, 

discussions with peers, attendance at conferences and 

seminars, detailed review of a patient's family, personal, and 

medical histories, and thorough physical examinations 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 diagnosis of the 

physician. The Federal Rules of Evidence recognize as much. 

See, e.g., Fed. R. Evid. 703 advisory committee's note ("[A] 

physician in his own practice bases his diagnosis on 

information from numerous sources and of considerable 

variety . . . . The physician makes life-and-death decisions in 

reliance upon them. His validation, expertly performed and 

subject to cross-examination, ought to suffice for judicial 

purposes."). 

We repeat that all of these reliable methods for making a 

diagnosis cannot sanitize an otherwise untrustworthy 

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 opinion 

proffered."). In this case, however, there is certainly evidence 

in the record--from Shaw's own records and from reliable 

studies--that carpets emit VOCs and that VOCs can cause 

15 

certain health problems. This might be sufficient to give Dr. 

Papano "good grounds" for making his conclusion, even 

though the District Court (or a jury) may not agree with that 

conclusion. Therefore, to the extent that the District Court 

excluded Dr. Papano's testimony on the basis that it 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 scientific 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 differential 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 alternative 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 categorically 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 need 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 "the basic 

method of internal medicine." Paoli, 35 F.3d at 755. Dr. 

Papano engaged in this basic method in a reliable manner, 

ordering standard laboratory tests, physically examining the 

16 

plaintiff, taking medical histories, and considering alternative 

causes of the plaintiff's illness. See id. at 755, 758. That he 

used this technique to "testify to a novel conclusion" is not 

sufficient grounds for excluding his testimony. Id. at 759 

n.27. Dr. Papano was not required to rule out all alternative 

possible causes of Heller's illness. Rather, only "where a 

defendant points to a plausible alternative cause and the 

doctor offers no explanation for why he or she has concluded 

that was not the sole cause, that doctor's methodology is 

unreliable." Id. 

When cross-examining Dr. Papano at the Daubert hearing, 

Shaw offered a number of plausible alternative causes, 

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 offer 

detailed explanations for why he concluded that these were 

not the causes of plaintiff's illness, but his responses, 

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 physical 

examination, certainly are more than "no explanation." See, 

e.g., App. at A602 (Dr. Papano's discussion of his 

consideration of other possible causes). Had the District 

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 were 

inadequate, but it did err in requiring him to "rule out all 

alternative possible causes." 

As we concluded in Paoli, a physician need not conduct 

every possible test to rule out all possible causes of a 

patient's illness, "so long as he or she employed sufficient 

diagnostic techniques to have good grounds for his or her 

conclusion." Paoli, 35 F.3d at 761. More recently, we held 
that a district court erred in excluding expert medical 

testimony because a defendant's suggested alternative causes 

(once adequately addressed by plaintiff's expert) affect the 

weight that the jury should give the expert's testimony and 

not the admissibility of that testimony. See Kannankeril, 128 

17 

F.3d at 808. In Kannankeril, we held that even absent hard 

evidence of the level of exposure to the chemical in question, 

a medical expert could offer an opinion that the chemical 

caused plaintiff's illness. See id. at 809. The medical expert 

there relied primarily on the temporal relationship and the 

nature of the plaintiff's complaints, as in the present case. 

While the potential harm of the chemical in that case was 

clearer than in this case, there was also some information 

indicating that there may not have been a harmful level of the 

chemical in Kannankeril's home. Nonetheless, we emphasized 

that the district court should take care not to "mistake 

credibility questions for admissibility questions." Id. If the 

medical expert's "opinion on causation has a factual 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 dispute that 

studies linking Shaw carpeting to such illnesses do not exist. 

Rather, they rely heavily on the temporal relationship 

between the installation of the carpeting and the onset of 

Heller's illness, as well as the fact that she appeared 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 plaintiff's 

illness is fatal to a plaintiff's case on causation. However, as 

noted, some reliable basis for a causation conclusion 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 prove 

causation unmet. We review the factual findings of the 

District Court for clear error and can find none, as the 

18 

background facts to its critique of Dr. Papano's temporal 

conclusion are undisputed: (1) the Shaw carpeting was 

installed in the Heller home in mid-December 1993; (2) Carol 
Heller first experienced respiratory problems no earlier than 

late December 1993; (3) Mr. and Mrs. Heller experienced 

renewed symptoms upon returning to the home in May 1994, 

almost a week after the carpet had been removed; and (4) 

although Dr. Papano originally relied on the same temporal 

relationship to conclude that the carpeting was the cause of 

Thomas Heller's illness, Mr. Heller actually experienced his 

symptoms prior to the installation of the Shaw carpet. 

In reaching its legal conclusion regarding the temporal 

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 testified that a 

reaction to VOCs in the home would typically occur within 24 

hours of exposure to the VOCs. See App. at A638. While 

Heller contends that this can be explained by her use 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 Shaw carpet. 

Not only did Heller's symptoms not appear until at least 

one or two weeks after the Shaw carpeting was installed, but 

they remained after the carpet was removed in May 1994. 

The District Court properly faulted Dr. Papano's testimony for 

not accounting for this fact as well. Plaintiff attempts 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 21 n.6. This 

explanation is dubious, however, as the air was actually 

_______________________________________________________ 

7. Plaintiff relies on the testimony of her other expert, Alan 

Todd, to establish the level of VOCs at the time the carpet was 

installed in mid-December. While we find serious problems with 

his calculations, see infra Part III.B.2, we note that 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 experts, 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 virtually no 

VOCs present at that time. Further, this "sink" effect theory 

was disavowed by Heller's own environmental expert. See 

App. at A882-883. Most importantly, it is not evident that Dr. 

Papano relied on any "sink" effect or any other explanation 

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 Shaw 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 conclusion 

for abuse of discretion, as noted above, our review of the 

court's legal analysis--i.e., whether it properly followed Rule 

702 as prescribed in Daubert and Paoli--is plenary. The 

court's analysis of the temporal relationship included the 

criticism that "plaintiffs proffer no statistical evidence to show 

the existence of a statistically significant correlation" between 

the Hellers' symptoms and their exposure to the Shaw 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 required is that 

the physician have "good grounds" for his or her diagnosis. 

See Paoli, 35 F.3d at 744 (noting that, even if the judge 

believes "there are better grounds for some alternative 

conclusion" and that there are some flaws in the expert's 

methods, if there are "good grounds" for the expert's 

conclusion, it should be admitted). Further, when the 

temporal relationship is strong and is part of a standard 

differential diagnosis, it would fulfill many of the 

Daubert/Paoli factors. See id. at 742 n.8. 

Here, however, we have no problem concluding that the 

temporal relationship between the exposure to the Shaw 

carpeting and the onset of Heller's illness was questionable 

20 

at best and exculpatory at worst. While the district court may 

not reject an expert's conclusion simply because the court 

finds it wanting, it is surely within the court's province to 

ensure that the conclusion, particularly a medical expert's 

ultimate conclusion on causation, "fits" with the data 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 suffered 

no reaction upon return to their home after the Shaw carpet 

was removed in May 1994, this would be the type of temporal 

relationship that might reliably support a conclusion that the 

carpet was the cause of plaintiff's illness. However, that is not 

the case here. 

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

extent that it required Dr. Papano's testimony to be backed 

by scientific studies linking the type and level of VOCs 

detected in the Heller home to Heller's illness, and to the 

extent that it required Dr. Papano to rule out all other 

possible causes of Heller's illness before concluding that the 

Shaw carpet was the cause. The District Court could, 

however, properly consider the fact (rather than requiring it 

as a prerequisite to admissibility) that Dr. Papano relied on 

few, if any, studies linking exposure to the VOCs allegedly 

emitted by the Shaw carpet to the illnesses suffered by Heller. 

It could also properly consider Dr. Papano's (weak) responses 

to Shaw's proffered alternative theories on the cause of 

Heller's illness in evaluating whether he truly had "good 

grounds" to arrive at the causation conclusion he reached. 

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 err in 

concluding that this relationship was unreliable. Without 

either scientific studies pointing to VOCs of the type and 

21 

amount detected as the culprit or a reliable temporal 

relationship, Dr. Papano was left with no valid means for 

concluding that the Shaw carpet was the cause of Heller's 

illness. Dr. Papano's conclusion had to "fit" with the data and 

the methodology that precedes it. See Paoli, 35 F.3d at 746. 

Even if the data (e.g., the medical history, the laboratory 

studies, evidence of VOCs in the Heller home) and the 

methodology (i.e., the differential diagnosis) were reliable, the 

District Court did not err in finding that the conclusion Dr. 

Papano reached did not reliably flow from this data and 

methodology. Under these circumstances, the District Court 

did not abuse its discretion in ultimately deciding to exclude 

Dr. Papano's testimony regarding the cause of Heller's 

illness.8 

B. Alan Todd 

Plaintiff's second expert witness, Alan Todd, of Todd 

Environmental Consultants, opined in his initial expert report 

that "the illness[es] suffered by the Heller family were caused 

_______________________________________________________ 

8. We add that the District Court should not necessarily have 

excluded all of Dr. Papano's testimony. In many cases, 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 medical 
expert should be permitted to "testify about his examination of 

[the plaintiff], the tests he conducted, and the diagnosis 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 testify 

regarding the nature of Ms. Cavallo's illnesses . . . . Rather, 

the focus of the dispute is whether his opinion regarding the 

cause of these illnesses is scientifically valid and therefore 

admissible under Daubert." (first emphasis added)). Thus, even if 

it was proper to exclude Dr. Papano's expert testimony regarding 

the cause of Heller's illness, as we conclude it was, testimony 

as to his examination and treatment of her illness was almost 

certainly relevant and reliable. It would be relevant 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 of her 

injuries, a relevant factor in any damages analysis). Of course, 

without Dr. Papano's causation testimony, summary judgment may 

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

without it there was insufficient evidence of causation to get to 

the jury. 

22 

by their prolonged exposure to the VOC's measured in their 

home and emitted by the carpeting manufactured by Shaw 

Industries." Todd based his conclusion on his testing of the 

air in a closet of the Heller home in which the Shaw carpet 

had been installed, and on his extrapolation from the results 

of these closet tests. He thereby estimated the level of VOCs 

emitted by the Shaw carpet at the time it was installed, 

approximately four months prior to his testing. We note 

preliminarily that we are doubtful that a non-medical expert 

such as Todd is qualified to testify as to the cause of 

someone's illness.9 We need not address that issue here, 

however, because we conclude that the District Court did not 

abuse its discretion in excluding Todd's extrapolations as 

being unreliable so that any arguable basis for Todd's 

causation conclusion was missing, making it appropriate for 

the District Court to exclude Todd's causation testimony. 

Todd is a certified industrial hygienist, who consults on 

environmental problems in occupational and residential 

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 normal 

'background' level," Paoli, 916 F.2d at 860-61, and that this 

exposure came from defendant's carpet, see id. at 860, 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 parts per 

billion ("ppb"), and that this benzene came from the Shaw 
carpet. He also estimated that, at that time, the level of other 

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

_______________________________________________________ 

9. While Todd was knowledgeable about studies on VOCs and 

illness, and on recommended maximum occupational VOC 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 the source and 

level of VOCs in the Hellers' house or his expertise regarding 

dangerous levels of VOCs, his qualification to offer an opinion 

on the ultimate cause of the Hellers' illnesses is another 

matter. 

23 

came from the Shaw carpet. If his methodologies were 

reliable, and his application of these methodologies 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 diagnosis 

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 emitted 

by the Shaw carpet, the only item present for the first test 

and absent for the second one. If the methodology for 

collecting air samples and for measuring the VOCs present in 

the air was valid and reliable, and the difference in the level 

of VOCs was significant, this part of Todd's testimony would 

be probative of whether or not the Shaw carpeting emitted 

VOCs, and should have been admitted. 

While the District Court faulted Todd's subtraction

methodology on a number of counts, we uphold its decision 

to exclude this testimony largely because the conclusions 

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 all of which 

we find warranted) before turning to our own critique of his 

testimony. 

The District Court found that the studies cited by Todd for 

the proposition that carpet such as Shaw's could cause 

Heller's illness did not support this conclusion. See Heller, 

1997 WL 535163, at *9. We address this aspect of the matter 
_______________________________________________________ 

10. Although not so labeled by Todd, the parties and the 

District Court utilized the terms "subtraction methodology" 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 Todd's 

subtraction methodology itself was valid and reliable.11 

In addition, although Todd testified that he used an 

accepted methodology for collecting the air samples and 

described this method in detail, Shaw and the District Court 

criticized him for not using some other test, specifically 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. Further, the 

record provides ample evidence that laboratory tests 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, SA1013, 

SA1030. That expert also admitted using in a prior study 

essentially the same "subtraction method" used by Todd. See 

_______________________________________________________ 

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 before a 

qualified expert may opine that a product emits a certain 

compound or causes a certain irritation, if the basis for the 

opinion is otherwise reliable and scientifically valid. 

Further, this aspect of Todd's testimony was based on first-hand, 

field testing of the object in question--the Shaw carpet. If Todd 

was qualified to conduct such tests, and if his means of 

collecting air samples was scientifically valid and the initial 

conclusion he drew--that the Shaw carpet was the source 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 "non-scientific." 

See, e.g., Carmichael v. Samyang Tire, Inc., 131 F.3d 1433, 1435- 

36 (11th Cir. 1997) (finding that testimony based on "skill- or 
experience-based observation," rather than on "application 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 testimony met the 

requirements of Daubert in that it was reliable and valid. 

25 

id. at A1152-1157.12 Properly performed, such on-site 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 closet (and 

the house) remained constant and that the environmental 

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 true that the 

concentration of VOCs is affected by more than the emission 

from a source such as carpeting, a substantial decline in the 

amount of VOCs would constitute strong (and reliable) 

evidence that at least some of these VOCs were coming from 

the Shaw carpet--the only item that was removed before the 

lower readings were taken. 

Our decision does not turn, however, on the validity of 

Todd's air sampling methodology, i.e., on whether the 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 VOCs detected 

by Todd's closet tests, even if they could all be attributed to 

the Shaw carpet, were substantially lower than any amounts 

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

_______________________________________________________ 

12. The court also faulted Todd's testimony because he "did not 

conduct further tests to ascertain whether changes in the levels 

of VOCs were attributable to the removal of the carpet or whether 

the changes were attributable to the natural fluctuation in VOC 

levels within the home." Heller, 1997 WL 535163, at *12. It is 

not clear what "further tests" the District Court would have 

required. Todd did not take snapshot tests at single moments, 

which would have been subject to natural fluctuations and random 

error; such tests likely would not be reliable enough to meet 

the Daubert standard. Rather, Todd took air sample readings over 

eight hours on one day, with the carpet present, and then took 

readings for eight hours on a second day, without the carpet 
present. 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) for each of the 

VOCs.13 A number of studies cited by the parties and 

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 home. See, 

e.g., App. at SA0835-0840 (finding basic irritation at 50-750 

ppb of VOCs; headaches at 750-6250 ppb; and additional 

neurotoxic effects at levels above 6250 ppb); id. at 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 ppb overall 

and about 3 ppb indoors, see id. at SA0200, actually above 

the levels (2.2 ppb) detected in the Heller home in April, when 

the Shaw carpet was still in the house.14 

_______________________________________________________ 

13. We note that a number of the VOCs allegedly attributable 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 detected in 

April 1994; the lowest suggested limit for exposure to benzene is 

500 ppb. Other VOCs detected in the closet, with the maximum 

amount attributable to the Shaw carpet and the lowest recommended 

limit, include: 

VOC Amount Found Recommended 

 (in ppb) Limit (in 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 that 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 industry 

documents to Todd's findings can be difficult, as the latter are 

reported in terms of ppb (parts per billion), while many of the 

studies and industry documents measure air concentration in mg/m3 

(milligrams per cubic meter) or ug/m3 (micrograms per cubic 
meter). The conversion from one to the other is 

27 

Todd attempted to address this shortcoming in his 

testimony by dividing the suggested occupational limits by 

420, based on two assumptions whose validity is problematic. 

First, because the limits are based on a 40-hour work week 

and there are potentially 168 hours per week in which a 

person could occupy her home (if she never left), Todd 

reduced the limits by 4.2. Then, because the occupational 

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 the home is 

actually approximately 1.2 ppb (i.e., 500 ppb / 420), slightly 

lower than the amount attributable to the Shaw carpet. 

This methodology is suspect. In one study in the record, 

the American Society of Heating, Refrigeration, and Air 

Conditioning Engineers ("ASHRAE") is cited as recommending 

a maximum level of contaminants arrived at by dividing the 

OSHA limit by 10, see App. at SA0860-0861, for essentially 

the same reason that Todd gave for dividing the permissible 

limits by 420. The OSHA limit for benzene is 1000 ppb; the 

ASHRAE limit, then, would be 100 ppb, still well above the 

amount detected in the Heller home in April (2.22 ppb). The 

OSHA limit for 2-butoxyethanol is 25,000 ppb, making the 

ASHRAE limit 2500 ppb, significantly higher than the 

amount detected in the Hellers' house (5.60 ppb). At all 

events, even if the methodology is valid, the levels measured 

in April (the earliest period at which Todd actually took air 

concentration measurements) do not even approach the 

(modified) recommended maximums for any of the other 

VOCs. 

Thus, while the closet tests conducted by Todd were not 

necessarily unreliable, because the level of VOCs detected 

_______________________________________________________ 

different for every compound. For benzene, it is about 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 analyzing 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 low 
and so close to background levels, the District Court did not 

abuse its discretion in excluding Todd's testimony that the 

Shaw carpet was emitting VOCs sufficient to cause Heller's 

illness--a conclusion that was unreliable if based on the 

closet tests alone. Todd, however, attempted to reinforce his 

closet tests--and to provide a stronger foundation for his 

opinion about the dangerous level of VOCs in the house--by 

introducing his back-extrapolation methodology in a

supplemental expert witness report (issued in March 1997, 

following his original January 1997 report). We turn to this 

aspect of his testimony. 

2. Back-Extrapolation Methodology 

If Todd's sampling of the air in the closet: (1) was reliable 

and adequately controlled for factors other than the Shaw 

carpet, and (2) demonstrated that the Shaw carpet was 

emitting VOCs at potentially harmful levels, his testimony 

would be sufficiently reliable to meet the Daubert standard 

and hence would be admissible. While we believe that the 

first proposition may be true, as noted above, the closet tests 

themselves fail to demonstrate the second. If it was 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 compounds 

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. Bottling Co., 161 

F.3d 77, 85 (1st Cir. 1998) (approving of a back-extrapolation 

and half-life methodology that "has been subjected to, and 

survived, the rigors of testing, publication, and peer review, 

and . . . appears to have won significant (if not universal) 

acceptance within the scientific community"). Here, however, 

it is clear that Todd's formula for his extrapolation was based 

29 

on speculation and estimation that was subject to gross 

error, and that the District Court did not abuse its discretion 

in excluding Todd's testimony based on the backextrapolation.15 Indeed, we doubt that Todd's backextrapolation methodology would meet even one of the eight 

suggested factors from Daubert and Paoli. 

Heller argues that the back-extrapolation method is "a 

standard reversibility of chemical processes equation," 

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 in the air. 

Todd's back-extrapolation method relies on at least three 
questionable 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 from 

carpets; and (3) the concentration of VOCs in the air is not 

affected by anything other than its natural half-life decline. 

None of these assumptions, however, appears supported by 

reliable scientific methods or the reliable application of any 

valid theory. In fact, Todd admitted as much in his own 

testimony and expert report. See, e.g., App. at A350-351, 

A761-762; id. at SA0247 (Todd's Expert Report: "The precise 

magnitude of difference quantitatively in off-gassing 

emissions at the carpet between April 1994 and December 

1993 is not readily evident from the published literature and 

or studies conducted by the rug manufacturers or their trade 

associations."). In fact, numerous published studies and 

industry documents consistently demonstrate that the actual 

rate of decline of emissions from carpet is nothing like a half- 

_______________________________________________________ 

15. Plaintiff relies heavily on a Louisiana state case to 

support Todd's back-extrapolation theory. See Appellants' 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 Daubert 

criteria were met, as required by Louisiana law. See 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, A242, A248-250, 

A268-270, SA0860, SA0956, SA1020. Rather, emissions

decline rapidly in the first hours and days after installation, 

reaching a level of about 10% of the original emission rate in 

only one week and as low as .05% of the initial emission rate 

in only one month. The differences between the emission 

rates indicated in these studies and those estimated by 

Todd's back-extrapolation theory are fairly substantial. (We 

express them graphically in the margin.16) For example, 

under Todd's theory, about ten days after installation of new 

carpet, VOCs would remain at levels approximately 50% of 

their initial level, while the studies in the record indicate that 

the levels would actually be less than 10% of their initial 

level. Within three weeks of installation, under Todd's theory, 

_______________________________________________________ 

16 
31 

VOCs would be at 25% of their initial level, while the studies 

show that carpet, at this point, is emitting only about 1% of 

the initial amount of VOCs emitted at the time of installation. 

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 exercised its 

discretion to exclude this part of Todd's testimony. 

Heller contends that even if Todd's "calculations were 

imprecise, it is undisputed that the level of VOC emissions in 

December 1993 were significantly higher than the VOC levels 

measured in April 1994." Appellants' Br. at 10 n.2. The 

problem with this argument, however, is that even if the 

levels were higher in December 1993, the calculations of 

plaintiff's expert were "imprecise" because his methodology 

was unreliable, and therefore Heller has presented no reliable 

evidence to demonstrate what the actual (or even reliably 

estimated) level of VOCs was in December 1993. Without a 

reliable method to determine how much higher the levels 

were in December 1993, only the actually measured levels in 

April 1994 are admissible evidence--and, as noted above, 

these levels were far too low to prove that the Shaw carpet 

was emitting harmful levels of VOCs. 

There are other flaws in Todd's back-extrapolation 

testimony that also support the District Court's decision to 

exclude this testimony. First, Todd conflates emission 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 emission rate: 

VOCs are emitted at a certain rate at the time of carpet 

installation; by 24 hours later, they are emitted at 

approximately half this rate; by a week later, they are emitted 

at approximately 10% the original rate, etc. The air 

concentration of VOCs (which is what Todd measured in the 

closet in April and May 1994, and used as the starting point 

for his back-extrapolation) is a function of not only the rate 

at which VOCs are emitted from the carpet to the air, but 

also such factors as the rate at which VOCs dissipate in the 

air, the size of the room or house in which the VOCs are 

32 

emitted, the molecular weight of the particular VOC, the rate 

of air flow, the moisture, light, and air temperature in the 

room, and other factors. See, e.g., John C. Little et al., 

Modeling Emissions of Volatile Organic Compounds from New 

Carpets, 28 Atmospheric Env't 227 (1994) (describing 
development of a model indicating that air concentration of 

a VOC is a function of time, distance from carpet, diffusion 

rate of the VOC, carpet thickness, air flow rate, carpet and 

room area, and air volume). Therefore, to measure the air 

concentration at one point in time (as Todd did) and to 

attempt to estimate the air concentration four months 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 which Todd 

considered in his back-extrapolation formula. 

Second, there is at least one study in the record that 

appears to indicate that while emission rates of VOCs decline 

rapidly (see supra note 16), air concentration levels remain 

fairly constant after an initial slight increase, making Todd's 

conflation of these two factors even more problematic. See 

Alfred T. Hodgson et al., Emissions of Volatile Organic 

Compounds from New Carpets Measured in a Large-Scale 

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 rapidly, 

while air concentration rates fluctuate within a relatively 

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-extrapolation 

theory, it would actually invalidate his closet studies, 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-butoxyethanol, 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 

33 

carpet that caused the levels of these VOCs to decline. 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 without the 

removal of the Shaw carpet; it actually declined to only 0.55 

ppb. The 2-butoxyethanol would have been expected to 

decline from 5.6 ppb to approximately 1.0 ppb; it actually 

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 20,000 

ppb for this compound. The District Court noted this 

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 have been 

overly critical of Todd's closet tests and that those aspects of 

its unreliability finding may have been inconsistent with the 

exercise of sound discretion, given the patent unreliability 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 the District 

Court did not abuse its discretion in excluding all of Todd's 

testimony. Cf. Paoli, 35 F.3d at 749 n.19 (noting that 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 causation or 

Todd's testimony on the allegedly higher levels of VOCs in 

December 1993 (both of which we hold the District Court 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 

34 

summary judgment at least in part because "defendant's 

carpeting is not the obvious cause of plaintiffs' illnesses." 

Heller, 1997 WL 535163, at *18. This appears to place 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 causal 

connection between Heller's illness and the Shaw carpet to 

survive. However, without Todd's testimony, plaintiff has 

failed to offer admissible proof that the Shaw carpet was 

defective. The only claim that does not require proof 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 evidence of record 

to support plaintiffs' assertion that they were injured by 

reliance on [Shaw's] alleged misrepresentation."). 

The order of the District Court granting summary judgment 

to Shaw will be affirmed. 

A True Copy: 

Teste: 

 Clerk of the United States Court of Appeals 

 for the Third Circuit 
35