Heller v. Shaw Industries, Inc.

Opinions of the United

1999 Decisions 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Precedential or Non-Precedential: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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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 non-

moving 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 cross-

examination, 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 peer-

reviewed 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 on-

site 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 back-

extrapolation.15 Indeed, we doubt that Todd's back-

extrapolation 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

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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 back-

extrapolation 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

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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

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