# FILED
September 29, 1997 Cecil W. Crowson Appellate Cou rt Clerk IN THE SUPREME COURT OF TENNESSEE AT NASHVILLE

FOR PUBLICA

TION Filed: September 29, 1997 KENNETH McDANIEL, ) ) Plaintiff-Appellee, ) DAVIDSON CIRCUIT ) ) Vs. ) HON. MARIETTA M. SHI PLEY, ) JUDGE ) CSX TRANSPORTATION, INC., ) ) Defendant-Appellant. ) No. 01-S-01-9605-CV-00095

For Appellant: For Appellee: Wayne L. Robbins, Jr. Van Kirk McCombs, II Gareth S. Aden James H. Wettermark GULLETT, SANFORD, BURGE & WETTERMARK, P.C. ROBINSON & MARTIN, PLLC 2300 SouthTrust Tower Nashville, Tennessee 37219 Birmingham, Alabama 35203-3204 Edward H. Stopher BOEHL, STOPHER & GRAVES Suite 2300, Providian Cent er 400 West Market Street Louisville, Kentucky

40202-3346



## O P I N I O N

AFFIRMED. ANDERSON, C. J.-2- We granted this interlocutory appeal to clarify the standards for the admissibility of scientific evidence under Tennessee R ules of Evidence 702 and 703.

The trial court, after a Tenn . R. Evid. 104 pretri al evidentiary hear ing, admitted into evidence the tes timony of plaintiffs’ experts who relied on epidemiological studies to prove that exposure to organic solvents caused a form of brain damage known as toxic encephalopathy. The trial court foun d that this scientific evidence w

ould substantially ass ist the trier of fact and was reliable and trustwort hy.
The Court of Appeals denied an interlocutory appea l. We, however, granted the interlocutory appeal and conclude that Tenne ssee Rules of Evidence 702 and 703 impose a duty upon trial courts to determine whether scient ific evidence will subs

tantially aid the tri er of fact and whether the underly ing facts and data relied on by the ex pert witness indicate

a lack of trustworthine ss. The trial court must f urther determi ne whether the rea soning or metho dology underlying the scientific evidence is sufficiently valid and reliable, and whether it can properly be applied t o the facts at issue.
In making this determinatio n, the trial court should focus on the principles and methodology underlyi ng the science, and not on the c onclusions of experts. The trial court is not required to de termine that t he principles an d methodology employed are generally accepted by the scientific community. The court needs only to determine that the pr inciples and methodology are scientifically v alid and reliable.

When these standa rds are applied in this case, the scientific evidence proffered by the plaintiffs should be ad mitted. Accordingly , we conclude that the1 The particul ar solvent s at issue i n this case ar e: tri chloroethan e, tri chloroethy lene, perchlo roethylene , and m ineral spirits.

2 Epidemiology

is the “study of the distri bution and det erminants of heal th-rel ated state s and events in populations and the application of this study to control of health problems.” Reference Manual on Sci entifi c Evidence , Federal Judi cial Cente r, p. 174 ( 1994)(herei nafter
“ Reference Manual ”). There are two g eneral type s of epide miolog ical studies which ar e used to test a hypothesi s: (1) cohor t studi es and (2) case-cont rol studi es. In a cohor t study , the epi demiologist identi fies a group o

f indi viduals who have been exposed to t he chemical and another group of indivi duals who have not been exposed to the chemical. The epi demiologist chooses two groups as nearly

identi cal as possibl e except for exposur e to the chemical . The inci dence rates of disease of t he exposed and non-exposed gro ups over a peri od of time is then observed. A casecontrol st udy invol

ves persons who either have the di sease (cases) or do not have the di sease (controls ). The c ases a nd con trols are m atched for com parison . A determ ination is m ade as to whethe r the individua ls in the cas e and c ontrol grou ps were expos ed to the c hem ical. -3- trial court did not abuse i ts discretion in denyi ng the defendant’s motion in limi ne which sough t to exclud e the pla intiff s’ expert t estimon y.

BACKGROUND This case involves ei ghty-four (84) cases filed pursuant to the Federal Employers Liability

Act, 45 U.S.C. § 51, et seq ., by employees of the defendant CSX Transportation, Inc. ( “CSXT”), a railroa

d operator, which w

ere consolidated for motions and case management in the Davidson Coun ty Circuit Court. Each plaintiff alleges that he has suffered brain damage due to chronic ex posure to four (4) particular organic solvents 1 while working in the CSXT mechanical shops in Nashville, Tennessee.
The plaintiffs intend to rely upon occupational physicians to show that long-term, low dosage exposure to the solvents has caused a form of brain damage known as toxic encephalopathy, which i s marked by diminished shortterm memory, sleeplessness, depression and anxiety. The plaintiff s’ experts rely upon epidemiological studies, 2 which they contend est ablished the causation between long term expos ure to solvents and damage t o the central nervous system.3 After collec ting the data either using a coho rt or case -control s tudy, epidem iologists typica lly me asu re ris k us ing th e con cep ts of “ relativ e risk ” and /or “o dds ratio.” Coh ort stu dies yield a direct measure of

the risk of

brain damage accordi ng to the pr esence or absence of solvent exp osu re. T his dir ect m eas ure, k now n as t he re lative r isk, is the ra tio of th e incid enc e of b rain damage or “toxic encephal opathy’in the exposed group divi ded by the r ate in t he nonexposed grou p. If the relativ e risk is 1.0 , then there is no a sso ciatio n bet wee n solv ent e xpo sure and b rain damage. A relati

ve risk of 4. 0 indicat

es that t he risk of di sease in the expo sed group is fo ur times higher tha n the risk of diseas e in the une xpose d group

. Reference Manual at 148. By co ntrast, case-controlstudies ut ili ze an odds ratio in calcul ating ri sk. An odds rati o is based on a comparison of the odds of having a di sease when exposed to a suspect ed agent and when not expos ed. Reference Manual at 149. Rel ative r isk and odds rat io are genera lly similar i n most cases
. -4- CSXT sought to exclude the plaintiffs’ experts on the basis that their testimony was wi

thout sufficient scientific suppor t. CSXT contended that the epidemiological studies relied on by the plainti ffs did not consistently establ ish a causal connection with a relative risk or odds ratio that shows a statistically signific ant degre e of relia bility. 3 It concluded, therefore, that the proff ered expert testimony on the issue w ould not “substantially

assist” the trier of fact, a nd that the facts and data underlying the testimony shows a “lack of trustworthiness.”
At a pretrial Tenn. R. Evid. 104 evidentiary hearing, several expert witnesses for the plainti ff and the defendant offered their opinions concerni ng the effect of long-term exposure to low doses of the organic solvents involved in this litigation. The proof indicated that the solvents belong to a fa mily of organic solvents known as chlorinated hydrocarbons, while mineral spirits are generally distilled from petroleum products. The industrial utility of the solvents lies in their ability to dissolv

e grease.
The experts agreed that ther e is no objective diag nostic tool, (such as an MRI, CT Sca n, or X-Ray), that will su pport a di agnosis o f toxic en cephalo pathy, and that no biological mechani sm has been identified that demonstrates how exposure to the solvent s causes the damage. Moreov er, while the exper

ts agreed that acute exposure to high concentrations of the solvents can create dizziness, disorientation, and even unconsciousness, the allegations in this case involve exposure below the level neces sary to render a person unconscious.4 Baker’s report studied among other s, Hanninen (1991 & 1979); Baker (1988) ; Arli enSoberg (1979); Elofsson (19 80); Hane (1977); Bleeker (19 91); Bolla (1990); Parkinson (1990); Maizlsih (1985); and Spurgeon (1992 ). -5- One of the plaintiffs’ experts, Dr. Edward Baker, a physician specializing in occupational medicine with two masters degrees,one in public health and another in epidemiology,testified that he has authored tw enty-six articl es and four textbook chapters on the subject of the ef fects of exposure to solvents. He began studying the effects of sol vent exposure on the centr al nervous system while on the faculty of Har vard University

’s School of Public Health. He has summarized epidemiologic al studies conducted since 198 5 and has concluded that “these cross sectiona l studies, viewed in the aggregate, suppor t the view that chronic solvent exposure causes impairment of neurobeh avioral function.” Baker, “A Review

of Recent Research on Health Effects of Human Occupational Exposure to Organic Solvents,” Journal of Occupational Medicine , Vol. 36, No. 10 (Oct. 1994). 4 Baker testified that dose/response and degree of exposure were critical to the causation inquiry.
Another plaintiffs’ expert, Dr. Douglas Linz, also a physician specializing in occupational medicine, has author ed four articles on the effects of expos ure to solvents and has diagnosed patients with chronic encephalopathy. Like Baker, he has performed and review ed the epidemiological studi es on the subject and has concluded that “chronic low dose exposure to solvents can cause chronic encephalopathy.” Dr. Howard Frumkin, a physician with a doctorate in public health, has evaluated patients for solvent exposure, a nd has researched and written on the effects of exposur e on the central nervous s ystem. He testified that a sufficient degree of exposure over a sufficien t amount of time can cause toxic encephalopathy, and that the diagnosis of chronic encephalopathy from low5 The plaint iffs’ fourth exper

t, Dr. Mi chael Kelly, was th e examining physi cian who diagnosed the plaintiffs’ toxic encephalopathy. He described the “differential diagnosis” procedure he used in thi s regard. -6- dose exposure to solvents is generally ac cepted throughout the United St ates and the world. 5

In contrast, Dr. Phili p Edelman testified on behalf of the defendant that although dose response is critical to any tox icology study, “most” in the medical community of toxicologi sts did not accept the causal connection between low dose exposure to solvents and encephalopathy. Edelman, a physician who is board certified in toxic

ology and occupational/env ironmental medicine, criti cized the epidemio logical studies th at the plaintif fs’ experts relied upon for lackin g a good dose/response relationship and for failing to control f or confounding factors such as age, intellig ence, and the use of alcohol. Likew ise, Dr. Joseph McLaughlin, a Ph.D. in e pidemiology, testified th at the epidemiological stud ies on the relation between ex posure to solvents and tox ic encephalopathy failed to account for significant confounding facto rs. Finally, Dr. Robert James, a Ph.D. in pharmacology, testified th at he reviewed forty -five cross sectional

studies and determined that 84 percent supported the hypoth esis and 16 percent did not. He criticized the “pos itive” studies, how ever, for failing to acc

ount for the factors of age, intelligence, ex

perience, and alcohol consumpti on. In James’s opinion, the diagnosis of toxic encephalopathy from exposure to solvents was not generally accepte d in the m edical co mmunity.
After considering the testi mony of the experts and analy zing the pertinent studies, the trial court concluded that the proposed evidence was “grounded in scientific theory,” w

as “generally acce pted in the occupational health community,” and was trustworthy and reliable. Although denying the defendant’s motion to exclude the exper t testimony, the trial c

ourt recognized the need to develop a uniform and consistent body of law and granted the def endant’s6 Cross-sectiona l studi es involv e selecti on of individuals, regardless of exposure or disease stat us. Subjects f or such studi es are chosen eit her at random or vi a probabil ity sampling procedures, which allows for the exam ination of the prevalence of a disease in a representative sample of the popu lation. McCunney, “Epidemiology and Biostatics,” A Prac tical Appro ach to Occupational an d Environmental Medicine (2nd Ed.), ” at 349 . Case reports are n ot epidemiologi cal studi es, but merely reports of indivi duals who have been expose d to an agent and then report

symptoms associated wi th the di sease. Case report s usually

precede the i nstitution of formal epid emiological research, although they can be important i n determining whether an associati on exists bet ween an agent and a di sease or defect. For example, the medical community became aware of the associ ation bet ween the drug, Thalidomide, used by pregnant women as a sedative and bi rth defect s in thei r child ren as a resul t of case repor ts. -7- motion for an interlocutory appeal pursuant to Tenn. R. App. P. 9. Although the Court o f Appeals

denied the inter

locutor y appeal , we gr

anted th e appeal

to clar ify the standards for determining the admissibility of scientific evidence in this jurisdiction. We now affirm the trial court.

SCIENTIFIC LITERATURE We begin our analysis by rev iewing the relev

ant material that was submitted to the trial court and discussed by seve ral of the experts during the evidentiary hearing . In the 1970's, researcher s in certain Scandinavi ancountries, performing epidemiological studies using case report and crosssectional methods, 6 reported that neuropsychi atric symptoms may be i nduced by long-term exposu re to solvents. In 1 979, the Danish physician, Arlien- Soborg, coined the phrase “chronic painters’ syndrome,” i n a study done on seventy house painters. The report conc luded that the majority of the pai nters who had been exposed to organic s olvents, often through a per iod with acute intox

ication symptoms, had gradually developed signs of a chron ic brain syndrome. The symptoms included impaired memory, fatigue, personality change, hea daches, and irritability. Arlien-Soborg, et al., “Chronic Painters’ Syndrome - Chronic Toxic Encephalopathy in House Painters,” Acta. Neurol. Scand , 60:149-156 (1979). Other authors, including plaintiffs’ expert Dr. Edward Baker, have r eported that the Scandinavian studies s upported the hypothesis that t oxic encephalopathy occurs in individual s heavily exposed to solvents over a per iod of months to7 Other s tudies ref erence d by the pa rties supp orting the th eory include Axleso n, et al., 1976; Hanninen, et al. , 1976; Hane, et al. , 1977; Harkonen, et al. , 1977; Knave, et al. , 1978; Mikkelson, 1980; and Gregersen, et al., 1987, among others.

-8- years. See Baker, et al., “The Neurotox icity of Industrial Sol

vents: A Review

of the Literature, “ Am. J. of Indus. Med. , 8:207-217 (1985). 7

As the defendant contends, the Scandinav ian studies have been criticized for failing to prove that the painters’ symptoms w ere related to their occupational exposure to organic s

olvents and for the disappearanc e of evidence of impairment in twenty r

e-examined workers. See Errebo-Knudsen and Olsen, “Organic Solvents and Presenile Dementia (The Painters’ Syndrome): A Cr itical Review of the Danish Literature,” The Sci. of the Total Env’t , 48:45-67(1986); Gade et al., “Chronic Painter’s Syndrome. A Reanalysis of Psychological Test Data in a Group of Diagnosed Cases,” Acta Neurol. Scand ., 77:293-306 (1988).

Some studies have likew ise questioned the Scandinav ian studies. As one report indicates:
Studies outside Scandinavi a, mainly cross-sectional clinical studies, have not supplied convincing evidenc e to support the hypothesis of s olvent exposure ca using irreversible bra in damage . . . . The reason for this discrepancy might lie in differences of study design, incomparab le study populations, ins ufficient adjustm ent for c onfoun ding fact ors, and, perhaps most imp ortantly, differences in disease classification. Rasmussen et al., “Solvent-Induced Chronic Toxic Encephalopathy,” Am. J. Of Indust. Med. , 23:779-792 (1993); see also Willi amson, e t al., “A Pr ospective Cohort Study of the Chronic Effects of Solvent Exposure,” Environmental Res. , 62:256-271 (1993)(“cross sectional studies suffer f rom problems of possible confounding by a range of unknow n factors and also usually from poor estimates of exposure.”). Moreov er, other studies have r eached opposite results. See , e.g. , Spurgeon, et al., “Investigation of Dose Related Neurobehavioral Effe cts in Paintmakers Exposed to Low Levels of Solvents,” Occupational & Environmental-9- Medicine , 51:626-630 (1994)(cross s ectional study of 110 paintmaker s resulted in view that “long

term exposure at or below current compliance lev els does not result in damage to the central nervous system.”).
Despite the criticisms , textbooks and review articles recogniz

e the diagnosis of toxic encephalopathy. For example, in the chapter entitled “Organic Solvents and Related Compounds ” of the Textbook of Clinical Occupa tional and Environmental Medicine , the authors state that “ther e is currently sufficient support for the association of hig h long-term solvent ex posure with long-l asting psycho-organic sy

mptoms to consider this a cli nical reality.” R osenstock and Cullen, at p. 773 (1994).

Interna tional an d nation al governm ental he alth orga nization s also have recognized the synd rome. For example, at the World Health O rganization and Nordic Council of Ministers meeting in Copenhagen, Denmark, in June 1985, it was stated that “[c]li nical, epidemiological and experimental data indica te that long-term occupational ex posure to organic solv

ents may cause adverse effects in the central and the peripher al nervous systems.”

It was recommended that further “clinical, ex

perimental and epidemiologic al studies should be undertaken to gain further insight into the reversibili ty of the neurotoxic effects in duced by the solvents, their health significance and the dose-effe ct, dose-response relationships.” Id . at pp. 32-33.
The National Institute for Occupational Saf ety and Health (“NIOSH”) “Current Intelligenc

e Bulletin 48,“ issued on M arch 31, 1989, makes similar observations and recommends that producers and users inf orm their customers, that trad e associa tions and unions war n their work ers, and t hat prot ective equipment and worker education be used to reduce worker exposure -- at least-10- to concentrations specified i n exposure lists of OSHA and other organizations

. Id . at iii-iv.
Accordingly, as the trial court found, numerous epidemi ological studies support the diagnosis of toxic encephalopathy from exposure to solvents. W hile other reports have criticized the epidemiological studies, the diagnosis is recognized in tex

tbooks and journals, as w ell as by national and w orld health organizations. It i s with this backgr ound that we now turn to the legal principles governing the admiss ibility of scientific evidence.

SCIENTIFIC EVIDENCE Nearly 75 years ago, the test for determining the admissibility of scientific eviden ce was establi shed in the landma rk feder al case of Frye v. United Stat es , 293 F. 1013 (D.C. Cir. 1923). In Frye , which involv ed a polygraph examination, or lie detector, the court said that scientific evidence will be admissible only if it has “gained general acceptance in the particular field in which it belongs.” Id . at 1014. This rule, although foll owed by the vast majo rity of federal and state jurisdictions, incl uding Tennessee, was often cr iticized for being too restrictive of relevant evidence, par

ticularly new or

“cutting edge” sci entific theory, and too vague for uniform application

. See e.g. , Symposium on Science and the Rul es of Evidence , 99 F.R.D. 188 (1983)(and e xtensive authority

discussed therein).

The federal courts embarked on a new and less restrictiv

e course with the decision recently in Daubert v. Merrell Dow Pharmaceuticals , 509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993), by the U. S. Supreme Court where the Court reversed the 9th Circuit and determined that the “general acceptance” test set forth in Frye was superseded by Fed . R. Evid. 702: If scientific, technical, or other specialized know ledge will assis

t the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill,-11- experience, training , or education, may testify thereto in the form of an opinion or otherwise. According to the Court, Rule 702 requires a deter mination as to “whether the expert is proposing to testify regarding scientific knowledg e that will assist the trier of fact to understand or determine a fa ct in issue.” Daubert , 509 U.S. at 592, 113 S.Ct. at 2796. This determi nation requires the tri al court to consider “whether the reasoning or methodology underlying the testimony is scientifically valid and of whether the r easoning or methodology properly can be applied t o the facts in issue.” Id . In analyzing scientific validity or reliability, the trial court must focus on “principles and methodology, and not on the conclusions they generate.” Id ., 509 U.S. at 595, 113 S.Ct. at 2797.
A partial list of factors the Supreme Court deemed relevant to the inquiry included whether the theor y or technique has been t ested, whether it has been subject to peer review

or publication, whether there is a known or pot ential rate of error, and whether, as formerly required under Frye , it is generally accepted in the relevant scientific field. Id ., 509 U.S. at 593-94, 113 S.Ct. at 2796-2798. On remand, the Ninth Circuit Court of Appeals also considered whether the expert proposes to testify about res earch conducted independent of liti gation or whether the expert had formulated an opini on for the express purpose of tes tifying. Daubert v. Merrell Dow Pharmaceuticals, Inc. , 43 F.3d 1311, 1317 (9th Cir.)(“Daubert II”

), cert. denied , 116 S.Ct. 189, 133 L.Ed.2d 126 (1995).

Daubert ’s influence was felt in Joiner v. General Elec tric Co. , 78 F.3d 524, 530 (11th Cir. 1996), cert

. granted 117 S.Ct. 1243, 137 L.Ed.2d 325 (1997)

. There, the trial court rul ed that the plaintiff could not present expert testimony that his exposure to poly chlorinated biphenyls had caused lung cancer and granted the defendant’s motion for summar y judgment. On appeal, the E leventh Circuit, applying Daubert , emphasized:-12- In analyzing the admi ssibility of expert testimony, it is impor

tant for trial cou rts to kee p in mind t he separ ate fun ctions of judge and jury, and the i ntent of Daubert to loosen the st rictur es of Frye and make it easier to present leg itimate conflicting vi ews of experts for the jury’s considerati on.
The court stressed the trial court’s role was a narrow one: This gatekeeping role i s simply to guard the jury from considering as proof pure speculation present ed in the guise of legiti mate scientifically-based expert opinion. It is not intended to turn judges into jurors or surrogate scientists. Thus, the gatekeeping responsibility of the tr

ial courts is not to w

eigh or choose between conflicting scientific opinions, or to analyze and study the science in question in order to reac h its own scientific c

onclusions from the material in the field. Rather, it is to assure that ex pert’s opinions are based on relevant sci entific methods, processes, and dat a, and not on mere speculation, and that th ey apply to the facts in i ssue
. Id . at 530 (emphasis added). After app lying the Daubert inquiry and analy zing the principles and methodolog y underlying the pl aintiff’s scientific evidenc e, the Eleventh Circuit Cou rt of Appeals held that the trial court erred in excl uding the evidence.
Although the fed eral cour ts have de cided a ne w and less re strictive direction was appropr

iate, state courts are sti ll wrestling w ith the choice between Frye and Daubert . For example, in a case involving the exact same parties, issues, and experts as the present case, a Florida state circuit court, appl ied the Frye test, which was r

etained in that jurisdiction by the Florida Supr eme Court, and concluded that the epidemiolog ical studies were i nconsistent and that the criticisms of these studies - that the plaintiffs had f ailed to show the evidence was “generally

accepted” in the relev ant scientific community - were valid and, therefore, ruled that the evi dence was inadmissible. See Roy Lee Berry v . CSX Transportation, Inc. , No. 92-2167 (filed April 28, 1995).
On the other hand, in a federal case involving the exact same parties, issues, and experts as the subject case, the federal dis trict court for the8 Of c ours e, sc ientific evide nce also m ust b e rele vant b efor e it is ad mis sible. As s tated in Tenn. R. Evid. Rule 401, “[ r]elev ant evidence means evidence having any tendency t

o make the existence of any fact that is of consequence to the determinati on of the action more probable or less pro bable tha n it would be without the evidenc e.” -13- Southern District of Georg ia applied Daubert , and concluded that the evidence was admissible. The dist rict court found that the epidemiol ogical studies supported the plaintiff’s claim that exposure can cause impai rment, and found that the studies and results were scientifically valid and reliable not

withstanding the criticisms by oppo

sing experts and repor

ts. The court rejected the defendant’s claim that the plaintiffs must show causation with a relative risk or odds ratio of 2.0 or greater

. See Bob Allen, et al. v. CSX Transportation, Inc. , (S.D. Ga., filed Sept. 10, 1996).

THE TENNESSEE STANDARD After examining the basic legal principles governing the admissibi lity of scientific evidence and the change in direction by the federal courts, we tur n to Tennes see to cla rify our st andard o f admiss ibility.
In general, questions regarding the admissibility, qualifications, relevancy and competency of expert testi mony are left to the discreti on of the trial court. State v. Ballard , 855 S.W.2d 557, 56 2 (Tenn. 1993). The trial court’s ruling in this regard may only

be overturned if the discr etion is arbitrarily

exercised or abused. Id . The specific rules of evide nce that govern the iss ue of admissibility of scientific proof in Tennessee are Tenn. R. Evid. 702 and 703. 8 The former provides: If scientific, technical, or other specialized knowledge will substantially assist

the trier of fact to understand the evidence or to determine a fact in issue, a w itness qualified as an ex pert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwi se.
And Tenn. R. Evid. 703 states:-14- The facts or data in the particul ar case upon which an ex pert bases an opinio n or infe rence ma y be those perceived by or made known to the expert at or before the he aring. If of a type reasonabl y relied upon by experts in the pa rticular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence. The court shall disallow testimony in the form of an opinion or inference if the underl ying facts or data indicate lack of trustworthiness. The plaintiffs contend that the expert testimony in this case is reliable and that it will substantially assist the j ury on the issue of causation . The defendant argues that irrespective of Frye or Daubert , there must be adherence to the strict requirements contained in the language of the rules and also a reaso nable standard for proving causation. It contends that the plaintif fs’ scientific evidence is unreliable and must be ex cluded. The defendant argues that an epidemiological study

must show a relativ

e risk of greater than 2.0, which several courts have said means that a disease more likely than not was caused by the specific agent or event. See Daubert v. Merrell Dow Pharmaceuticals, Inc. , 43 F.3d 1311 (9th Cir. 1995), cert

. denied , 116 S.Ct. 189, 133 L.Ed.2d 126 (1995); Deluca v. Merrell Dow Pharmaceuticals, Inc. , 791 F.Supp. 1042 (D.N.J. 1992), aff’d , 6 F.3d 778 (3rd Cir. 1993). As discussed herein, the factor is certainly relevant but we rej ect the contention that it shoul d be adopted as matter of law.
Although the advisory

comments to Rule 702 indicate tha t Tennessee has followed the Frye test in analyzing the admissibility of scientific evidence, one commentator, recognizing the similarity betw

een Tennessee Rule 702 and Federal Rule Evid. 702,has raised the question of w hether the Frye test of “general acceptance” shou ld be abolished in Tennessee. N.Cohen, S. Sheppeard, and D. Paine, Tennessee Law of Evidence , § 401.20 at 124, n. 233.9 The trial judge ident ified four diff erent standar

ds used by Tennessee court s to determine admissibility of scientifi c evidence: (1) “Scientifically acceptable and accurate for its purpose.” State v. Johnson, 717 S.W.2d 298 (Tenn. Crim. App. 1986) ; (2) “Four -prong thresh old test involv ing whether the witn ess is an expert ; whether t he subject matter is proper; whether the subject matter conforms to a general ly-accept ed theory;and whether th e probativ e value of t he witness’ testimony outweighs its prejudicial effect.” State v. Schimpf , 782 S.W.2d 186 (Tenn. Crim. App. 1989); (3) “ Frye or Tenn. R. Evid. 702 and 703 .” State v. Ha rris , 866 S.W.2d 583 (Tenn. Crim. App . 1992); and (4) “Analysis under several tests” State v. Myers , 1992 WL 297626 (Tenn. Crim. App . 1992). -15- Indeed, as the tr

ial cou rt in th is case

noted, t here is

some evidence o

f a departure from the strict adher ence to the Frye test by courts in thi s State. 9
In our view, determining the standard for the admissibility of scientific evidence requires an analysis of the unique lan guage found in Rules 702 and 703 of the Tennessee Rules of Evidence. For instance, Tenn. R. Ev id. 702 requires that the scientific evidence “substantiallyassist the trier of fact,” w hile its federal counterpart requir es only that the evidenc e “assist the trier of fact.” Fed. R. Evid. 702. This dis

tinction indicates that the probative force of the testimony must be stronger before it i s admitted in Tennessee. See , e.g. , Weinstein, Rule 702 of the Federal Rules of Evi dence is Sound; It Should Not Be Amended , 138 F.R.D. 631, 636 (1991).
Similarly, Tenn. R. Ev

id. 703 states that “[t]he cour t shall disallow testimony in the form of an opinion o r inference if the underlyi ng facts or data indicate lack of trustw

orthiness.” There is no s imilar restriction i n the federal rule. Fed. R. Evid. 703. Thus, as one write r has observed, “th e additional la nguage . . . [in the Tennessee rule] i s obviously desig ned to encourage trial cour ts to take a more active role in evaluating the reasonableness of the expert’s reliance upon the particular basis for his or her testimony.”

R. Banks, Some Comparisons Between the New Tennessee Rules of Evidence and the Federal Rules of Evidence, Part II , 20 Mem.S.U. L. Rev. 499, 559 (1990). In sum, even though the facts and data need not be admis sible, they must be rev iewed and found to be trustworthy by the trial court.-16- Based on the foregoing analy sis, we conclude that Tennes see’s adoption of Rules 702 and 703 in 1991 as part of the Rules of Evidence supersede the general accepta nce test

of Frye . In Tennessee, under the recent r ules, a trial court must determine whether the evidence will

substantially assis

t the trier of fact to determine a fact in issue and whether the facts and data underl ying the evidence indicate a lack of trustworthiness. The rules together necessarily require a determination as to the scientific vali dity or reliabili ty of the evidence. Simply put, unless the scientific evidence is valid, it will not substantially assist the trier of fact, nor wil l its underlying facts and data appear to be trustw orthy, but there is no requirement i n the rule that it be genera lly accepted.
Although we do not expr essly adopt Daubert , the non-exclusive list of factors to determine reliabil ity are useful in apply ing our Rules 702 and 703. A Tennessee trial court may c onsider in determining r eliability: (1) whether scientific evidence has been tested and the methodology w ith which it has been tested; (2) whether the e vidence has been subjected to peer review or publication; (3) wheth er a potential rate of error is known; (4) wh ether, as formerl y required b y Frye , the evidence is generally accepted in the scientific community; and (5) wheth er the expert’s resear ch in the field has been conducted independent of litigati on.
Although the trial court must analyze the scien ce and not merely the qualifications, demeanor or c onclusions of experts, the c ourt need not weigh or choose between two leg itimate but conflicting scientific views. The c ourt instead must assure itself that the opinions are based on relevant scient ific methods, processes, and data, and not upon an ex pert’s mere speculation. See , e.g. , Joiner , 78 F.3d at 530. The trial court should keep in mind that the prelim inary question under Tenn. R. Evid. 104 is one of admissibility of the evidence. Once the evidence is admitted, it will thereafter be tes ted with the crucible of vigorous-17- cross-exa minatio n and cou ntervaili ng proof . After th at occurs , a defe ndant ma y, of course, challenge the sufficienc y of the evidence by mov ing for a directed verdict at the appropri ate times. See Tenn. R. Civ. P. 50. Y et it is important to emphasize that the weig ht to be given to stated s cientific theories, and the resolution of legitimate but competing scientific views, are matters appropriately entrusted to the trier of fact. See Joiner , 78 F.3d at 534-35 (Birch, J., concurring).
We recognize that the burden placed on tr ial courts to analyz

e and to screen novel scientific

evidence is a signi

ficant one. No framework ex ists that provides for simple and pr actical application in ev ery case; the complexi

ty and divers ity of potentia l scientific ev idence i s simply too v

ast for t he appli cation o f a single test. See Developments in the Law -- Confronting the New Challenges of Scientific Evidence , 108 Harv. L. Rev. 1481, 1513-1516 (1995). Nonetheless, the preliminary questions must be addressed by the trial court, see , Tenn. R. Evid. 104, and they must be addressed within the framew ork of rules 702 and 703.

APPLICATION OF STA NDARD The trial co urt correc

tly foresaw

the trend aw

ay from Frye and also used the factors set forth in Daubert as a framework for analys is. As it observed, the scientific theory that ex posure to solvents may cause toxic encephalopathy has been tested frequently over a period of 25 years. Because no precise diagnostic device or biologic

al mechanism can isolate the cau sal factor, the relevant t ests have been epidemiological studies. The experts in this case testified at leng th about the field of epidemiology and the use of cohort and case-contr ol studies. The experts agreed that epi demiological studies hav e been used to test the hypothesis that exposur e to solvents causes encepha lopathy and that numerous studies support a causal r elationship. These studies hav e been reviewed,-18- reconstructed, published i n leading journals in the field, and subjected to peer review. Althoug h the “positive” studi es have been criticiz ed for failing to account for confounding factors, the diagnos is is recognized in medical textbooks and journals as well as by several national and world health organizations. We also observe that the research in this area, including that of several of the plaintif fs’ experts, was conducte

d independently of this liti gation.
Accordingly, we agree with the trial court’s finding that the evidence will substantially assist the jury to understand the evidence and to determine a f act in issue. We also agree with the tri al court’s conclusion that the methodology and principles underlyi ng the scientific evid ence are sufficiently trust worthy and reliable to be presented to th e trier of fact. The trial cour t is not required to determine whether it ag rees with the evidenc e and should not substitute its view for the trier of fact. It should al low the jury to con sider legitimate but confli cting views about the scie ntific proof. Provided the ev idence is scientifically

valid, criticisms of it and opposi ng views may be elicited on cross exa mination and/or established in the defendant’s cas e. That is the essence of the law suit.

CONCLUSION We have conc

luded th at the scientifi c evide nce proff ered by the plai ntiffs satisfies the requirements of Tenn. R. Evid. 702 and 70 3, and that the trial court did not abuse its discreti on in admitting it into ev idence. The trial court’s order denying the defendant’s motion in limine is therefore a ffirmed and this case is remanded to the trial court for further proceedings. Costs of the appeal are assessed against the defendant.

________________________________ E. RILEY ANDERSON, CHIEF JUSTICE-19- Concur: Drowota, Reid, Birch and Holder, JJ.