F I L E D
                                                                   United States Court of Appeals
                                                                           Tenth Circuit
                                       PUBLISH
                                                                           JAN 7 1999
                      UNITED STATES COURT OF APPEALS
                                                                     PATRICK FISHER
                                                                                 Clerk
                                  TENTH CIRCUIT


 JEFFREY A. MITCHELL and VERNA
 MITCHELL, individually and as executors
 of the estate of Jeffrey A. Mitchell, Bryan
 A. Mitchell, a minor, by and through their
 mother, next friend,

       Plaintiffs-Appellants,
 v.                                                       No. 97-3219
 GENCORP INC.,

       Defendant-Appellee.



             APPEAL FROM THE UNITED STATES DISTRICT COURT
                      FOR THE DISTRICT OF KANSAS
                          (D.C. No. 94-4110-RDR)
                             (

)


David O. Alegria of McCullough, Wareheim & Labunker, P.A., Topeka, Kansas, for
Plaintiffs-Appellants.

Robert P. Numrich (Martha E. Madden with him on the brief) of Evans and Dixon,
Kansas City, Missouri, for Defendant-Appellee.


Before BALDOCK, MCKAY, and HENRY, Circuit Judges.


BALDOCK, Circuit Judge.
       Plaintiffs Jeffrey A. Mitchell and Verna Mitchell appeal the district court’s grant

of summary judgment in favor of Defendant Gencorp. Specifically, Plaintiffs argue that

the district court erroneously excluded the testimony of their expert witnesses and, as a

result, granted summary judgment in favor of Defendant because Plaintiffs failed to

establish causation. Our jurisdiction arises under 28 U.S.C. § 1291. We affirm.

                                             I.

       Jeffrey A. Mitchell worked as a warehouseman and truck driver for Midway Sales

and Distribution, Inc. from 1988 until 1993. Mitchell’s positions with Midway required

him to stock, organize and fill orders from the company’s “flammable room.” The

“flammable room” is twelve feet wide by thirty feet long with a ten-foot ceiling. The

room has no forced ventilation and the evidence before the district court suggests that

some barrels leaked in the room. During Mitchell’s tenure, the room contained, among

other things, products manufactured by Defendant which contained Toluene, Xylene,

Hexane and Haptene. Mitchell entered the “flammable room” several times each day and

remained for periods varying from less than one minute to as many as fifteen minutes.

       In 1992, doctors diagnosed Mitchell with chronic myelogenous leukemia. After

some investigation, Mitchell concluded that his exposure to Defendant’s products caused

him to develop chronic mylogenous leukemia. Accordingly, Mitchell filed suit seeking

compensatory and punitive damages from Defendant for negligence, breach of express

and implied warranties, and strict liability. Mitchell died on June 1, 1995, at which time


                                             2
his executor and several additional parties were substituted as Plaintiffs.

       Plaintiffs proposed to introduce five expert witnesses at trial. Plaintiff first

proposed to introduce the testimony of Steve Herron, an industrial hygienist. In forming

his opinion, Herron studied photographs of the “flammable room” and material safety

data sheets listing the chemicals contained in Defendant’s products. From this and his

general knowledge of chemicals, Herron opined that Mitchell’s exposure to Defendant’s

products probably caused him to develop chronic mylogenous leukemia. Herron never

visited the flammable room and conducted no air tests to demonstrate Mitchell’s level of

exposure to the chemicals. Moreover, he did not attempt to recreate the level of exposure

through computer modeling.

       Plaintiff also proposed to call four physicians at trial. Each physician examined

Mitchell and the material safety data sheets listing the chemicals contained in Defendant’s

products. The physicians had no information suggesting Mitchell had been exposed to

benzene, a substance thought to cause certain types of leukemia, and relied largely on

Mitchell’s personal recollection to determine his level of exposure to the chemicals in the

“flammable room.” In forming their opinions, the physicians reviewed several published

articles suggesting a relationship between benzene exposure and certain types of

leukemia. No article the physicians produced, however, showed a supportable link

between benzene exposure and chronic mylogenous leukemia; the type of leukemia from

which Mitchell suffered.


                                               3
       Prior to trial, Defendant filed a motion in limine seeking to prevent Plaintiffs’

experts from testifying. After a lengthy hearing held pursuant to Daubert v. Merrell Dow

Pharmaceuticals, Inc., 

(1993), the district court determined that “the

opinions of plaintiffs’ expert witnesses [were not] based on scientifically valid principles

and, therefore, [did] not meet the reliability requirements of Rule 702 as interpreted by

the Supreme Court in Daubert.” Based on this determination, the district court excluded

the evidence. Also pending before the court was Plaintiffs’ motion for summary

judgment. The district court determined that without the assistance of their expert

witnesses, Plaintiffs could not prove Mitchell’s exposure to Defendant’s products caused

him to develop chronic mylogenous leukemia. Therefore, the court granted Defendant’s

motion for summary judgment.

       Where a trial court excludes “evidence essential to maintain a cause of action, the

propriety of summary judgment depends, as here, entirely on the evidentiary ruling.”

Allen v. Pennsylvania Engineering Corp., 

, 196 (5th Cir. 1996).

Thus, we focus on the district court’s evidentiary ruling, which we review for an abuse of

discretion. General Electric v. Joiner, 

, 519 (1997). Once we determine the

propriety of the district court’s decision to exclude evidence, we must then determine

whether the district court correctly granted summary judgment in Defendant’s favor. This

we review de novo. Aramburu v. The Boeing Co., 

, 1402 (10th Cir. 1997).




                                              4
                                              II.

       Federal Rule of Evidence 702 allows the parties to present scientific testimony

through a qualified expert where such evidence “will assist the trier of fact to understand

the evidence or to determine a fact in issue.” In Daubert v. Merrell Dow Pharmaceuticals,

Inc., 

(1993), the Supreme Court defined the role of the trial judge in

admitting scientific testimony under Rule 702. Describing the trial judge’s role as that of

a “gatekeeper,” the Court listed several non-exclusive factors which it deemed relevant in

deciding whether to admit expert scientific testimony. 

n.7, 593-94. First, the

Court stated that the subject of the expert’s testimony must be based on scientific

knowledge. 

Scientific knowledge, the court explained “implies a grounding in

the methods and procedures of science” which must be based on actual knowledge and

not “subjective belief or unsupported speculation.” 

words, “an inference or

assertion must be derived by the scientific method . . . [and] must be supported by

appropriate validation – ie. ‘good grounds,’ based on what is known.” 

also

suggested that the trial court should consider a theory’s susceptibility to testing and

whether the theory has been subjected to such testing. 

       The Court next noted that a trial court may consider whether the theory has been

subjected to peer review. 

dispositive, subjecting a theory to the scrutiny

of the scientific community may help validate an otherwise infirm theory by decreasing

the likelihood that substantive flaws in the methodology exist. 

The Court


                                              5
also noted the importance of any known or potential rate of error associated with the

theory and the maintenance and existence of any standards controlling the technique’s

operation. 

Finally, the Court advised that a theory’s level of acceptance in the

scientific community may have some bearing on admissibility. 

can be an important factor in ruling particular evidence admissible, and a

known technique which has been able to attract only minimal support within the

community may properly be viewed with skepticism.” 

omitted).

       The court also noted that the proposed expert testimony must be sufficiently tied to

the facts of the case. 

The court described this aspect of the district court’s

inquiry as one of “fit.” 

not always obvious, and scientific validity for one

purpose is not necessarily scientific validity for other, unrelated purposes.” 

       It is well established that a plaintiff in a toxic tort case must prove that he or she

was exposed to and injured by a harmful substance manufactured by the defendant.

Wright v. Willamette Industries, Inc., 

, 1106 (8th Cir. 1996); Wintz By And

Through Wintz v. Northrup Corp., 

, 515 (7th Cir. 1997); Allen v.

Pennsylvania Engineering Corp., 

, 199 (5th Cir. 1996). In order to carry this

burden, a plaintiff must demonstrate “the levels of exposure that are hazardous to human

beings generally as well as the plaintiff’s actual level of exposure to the defendant’s toxic


                                               6
substance before he or she may recover.” 

. Although the district

court, in this case, did not focus on Mitchell’s level of exposure to Defendant’s

chemicals, our review of the record suggests that the information relied upon by

Plaintiffs’ experts with respect to Mitchell’s level of exposure was “so sadly lacking as to

be mere guesswork.” See 

.

       The record demonstrates that Plaintiffs attempted to establish Mitchell’s level of

exposure in two ways. First, Plaintiffs attempted to establish Mitchell’s level of exposure

through his own statements describing the number and length of visits he made to the

“flammable room.” Second, Plaintiffs attempted to set the level of exposure through

Steve Herron, an industrial hygienist, who after studying material safety data sheets and

pictures showing some chemical spillage, opined that Mitchell’s exposure to Defendant’s

products caused him to develop chronic mylogenous leukemia. These attempts fall short.

       While Mitchell’s testimony could be relevant to proving that the “flammable

room” contained chemicals, it does not clarify the level of chemicals to which Mitchell

was exposed. Similarly, the materials relied upon by Herron are not relevant in

determining level of exposure. It makes little sense to argue that a scientist can look at

pictures and a list of chemicals contained in a room and arrive at a level of exposure.

Moreover, Herron himself testified that there was no occupational exposure data.

       We believe a plaintiff must prove level of the exposure using techniques subject to

objective, independent validation in the scientific community. See Moore v. Ashland


                                              7
Chemical, Inc., 

, 276 (5th Cir. 1998) (en banc). At a minimum, the expert

testimony should include a description of the method used to arrive at the level of

exposure and scientific data supporting the determination. The expert’s assurance that the

methodology and supporting data is reliable will not suffice. 

of the harmful level of exposure to a chemical plus knowledge that plaintiff was exposed

to such quantities are minimal facts necessary to sustain the plaintiff’s burden in a toxic

tort case.” 

. Absent supporting scientific data, Mitchell’s estimates

and Herron’s conclusions are little more than guesswork. Guesses, even if educated, are

insufficient to prove the level of exposure in a toxic tort case. See 

(unsupported speculation and subjective belief insufficient to meet Fed. R. Evid.

702's reliability requirement).

                                             B.

       Under Daubert, proposed expert testimony must be supported by “appropriate

validation – ie., ‘good grounds,’ based on what is 

. The plaintiff

need not prove that the expert is undisputably correct or that the expert’s theory is

“generally accepted” in the scientific community. 

. Instead, the

plaintiff must show that the method employed by the expert in reaching the conclusion is

scientifically sound and that the opinion is based on facts which sufficiently satisfy Rule

702's reliability requirements. E.g., In re Paoli R.R. Yard PCB Litig., 

, 744

(3d Cir. 1994).


                                              8
       The physicians called by Plaintiffs testified that exposure to Defendant’s chemicals

caused Mitchell to develop chronic mylogenous leukemia. The physicians supported their

conclusions with various published works indicating a link between exposure to benzene

and certain types of leukemia. The physicians, however, had no information suggesting

that Mitchell was ever exposed to benzene.1 To compensate for this, the experts rendered

their opinions as follows: (1) Defendant’s products are chemically similar to benzene; (2)

because Defendant’s products and benzene are chemically similar, they should affect the

body in similar ways; (3) benzene exposure causes certain types of leukemia; (4) because

benzene exposure causes other types of leukemia, it is logical that it could cause chronic

mylogenous leukemia as well; (5) therefore, Mitchell’s exposure to Defendant’s products

caused him to develop chronic mylogenous leukemia. The district court found that the

doctors’ opinions lacked sufficient scientific validation to withstand the strictures of

Daubert.2

       1
          Although none of their experts delivered opinions based on the notion that
Mitchell was exposed to benzene, Plaintiffs vigorously argue that Mitchell was indeed
exposed to the chemical. In making this leap from exposure to chemicals whose material
safety data sheets do not list benzene as an ingredient to actual benzene exposure,
Plaintiffs offered the testimony of Steve Herron. Herron testified from “general
knowledge” that the chemicals in Defendant’s products are benzene derivatives. He
stated that during the distillation process in which benzene is removed from the
chemicals, that some benzene remains in the chemical. Herron neither named nor
produced any material supporting this theory. Moreover, he could not predict with any
certainty the amount of benzene left behind during the distillation process; a fact
undoubtedly important to determining Mitchell’s level of exposure.
       2
        Herron also testified regarding causation. He stated: “in my opinion, exposure
of Mr. Mitchell [to] high concentrations of these chemicals . . . probably more than not

                                              9
       In analyzing the experts’ opinions, we begin by noting that the record contains

some testimony about the similarities between benzene and Defendant’s products.

Missing from this evidence is additional testimony explaining exactly what these

similarities are and how the similarities cause the human body to respond to Defendant’s

chemicals in a manner similar to benzene. Nor does the literature Plaintiffs presented

support the notion that chemicals similar to benzene will affect the body in a manner

similar enough to cause the same response as benzene. We recognize that “[t]rained

experts commonly extrapolate from existing data. But nothing . . . requires a district court

to admit opinion evidence which is connected to existing data only by the ipse dixit of the

expert. A court may conclude that there is simply too great an analytical gap between the

data and the opinion proffered.”   

.

       Under Daubert, “any step that renders the analysis unreliable . . . renders the

expert’s testimony inadmissible. This is true whether the step completely changes a

reliable methodology or merely misapplies that methodology.” In re R.R. Paoli R.R. Yard

PCB Litigation, 

, 745 (3d Cir. 1994). Without scientific data supporting their

conclusions that chemicals similar to benzene cause the same problems as benzene, the




could have caused . . . [him] to develop cancer . . . .” Considering his testimony that no
exposure data existed and the fact that he failed to support his opinion with evidence of
the methods he used and the scientific data supporting his conclusion, the district court
correctly excluded his testimony.

                                             10
analytical gap in the experts’ testimony is simply too wide for the opinions to establish

causation. The district court reached this conclusion and did not abuse its discretion in

doing so.

                                              C.

       Assuming arguendo that exposure to Defendant’s products cause the same

problems as exposure to benzene, Plaintiffs’ attempt to link Mitchell’s chronic

mylogenous leukemia and his exposure to Defendant’s chemicals still fails. At the

Daubert hearing, Plaintiffs’ experts produced articles supporting their opinion that

exposure to benzene and certain types of leukemia are causally related. Some of the

literature suggested that there could be a connection between chronic mylogenous

leukemia and benzene exposure. Each of these articles, however, notes that the data

necessary to reach a conclusion on the issue is inadequate.

       Plaintiffs’ did present literature and testimony demonstrating some connection

between benzene exposure and acute mylogenous leukemia. Recognizing the difference

between acute mylogenous leukemia and chronic mylogenous leukemia, Plaintiffs’ then

elicited testimony from their experts to bridge the gap between the two types of leukemia.

The experts so testified, but in doing so failed to provide sufficient support for their

opinions.

       Some of Plaintiffs’ experts pointed to a sentence in an article they presented which

referenced a study finding some relationship between benzene and toluene and chronic


                                              11
mylogenous leukemia.3 Plaintiffs’ experts did not examine the study and did not produce

the study at the Daubert hearing. Furthermore, the article mentioning the study criticized

the study for failing to distinguish between benzene and toluene and for failing to provide

an estimate of dose-response. The district court determined that no “scientist would

attach weight to a study that he did not carefully examine and consider.” Therefore, it

gave no credence to the study. We believe it is crucial for experts to examine the studies

upon which they rely in forming a medical opinion. By examining the studies, the expert

may review the methodology employed by the scientist conducting the study and ensure

the quality of the assumptions and data on which the study relies. Such examination is

particularly important in cases, such as this one, where the article referencing the study

actually criticizes it.

       “Under the regime of Daubert . . . a district judge asked to admit scientific

evidence must determine whether the evidence is genuinely scientific, as distinct from

being unscientific speculation offered by a genuine scientist.” Rosen v. Ciba-Geigy

Corp., 

, 318 (7th Cir. 1996) (internal quotation omitted). Plaintiffs’ experts



       3
          Plaintiffs place a sizeable amount of weight on the fact that toluene is classified
as a carcinogen in the state of California. This reliance is largely misplaced. The
methodology employed by a government agency “results from the preventive perspective
that the agencies adopt in order to reduce public exposure to harmful substances. The
agencies’ threshold of proof is reasonably lower than that appropriate in tort law, which
traditionally makes more particularized inquiries into cause and effect and requires a
plaintiff to prove that it is more likely than not that another individual has caused him or
her harm.” 

(internal quotation omitted).

                                             12
appear on the record before us to be “genuine scientists.” Unfortunately, the analytical

gaps in their opinions are too broad for their testimony to endure under the strictures of

Daubert and Rule 702. The district court recognized this gap and did not abuse its

discretion by finding that the expert’s opinions were not reliable.

                                              D.

       We also find persuasive an additional ground on which the district court relied in

excluding two of Plaintiffs’ experts. Under Daubert, the “subject of an expert’s testimony

must be ‘scientific . . . knowledge’. The adjective scientific implies a grounding in the

methods and procedures of science.” 

. “Scientific method

today is based on generating hypotheses and testing them to see if they can be

falsified . . . .” 

The district court found that Drs. Van Veldhuizen and Milner

reached their ultimate conclusions before studying the available literature. “[This type of

action] turns scientific analysis on its head. Instead of reasoning known facts to reach a

conclusion, the experts here reasoned from an end result in order to hypothesize what

needed to be known but what was not.” Sorensen By And Through Dunbar v. Shaklee

, 649 (8th Cir. 1994). “[S]cientists whose conviction about the

ultimate conclusion of their research is so firm that they are willing to aver under oath

that it is correct prior to performing the necessary validating tests [may] properly be

viewed by the district court as lacking the objectivity that is the hallmark of the scientific

method.” Clarr v. Burlington Northern Railway Co., 

, 503 (9th Cir. 1994).


                                              13
We believe that the district court was properly concerned with the methods employed by

these two doctors and, therefore, did not abuse its discretion by discounting the testimony.

                                              E.

       We further note that several of the Supreme Court’s non-dispositive factors

support the district court’s decision. First, the opinions prepared by Plaintiffs’ experts

were not published and subjected to peer review. By failing to subject their opinions to

peer review, the experts missed the opportunity to have other scientists review their work

and warn them of possible flaws in their methodology. Second, the record lacks evidence

showing how the experts’ conclusions may be tested and the applicable rate of error.

Finally, the theories espoused by Plaintiffs’ experts are not generally accepted within the

scientific community.

                                             IV.

       In a meticulous memorandum and order, the district court thoroughly applied the

test set forth in Daubert and excluded Plaintiffs’ expert witnesses. For the foregoing

reasons, we believe the district court did not abuse its discretion by determining that

Plaintiffs’ proffered expert testimony was inadmissible. We further conclude that without

the benefit of their experts, Plaintiffs cannot prove causation. Accordingly, the district

court correctly granted Defendant’s motion for summary judgment.

       The district court’s judgment is AFFIRMED.




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