Moyer, C.J.
{¶ 1} The question presented in this appeal is whether Evid.R. 702(C) requires a scientifically valid connection between the opinion of an expert witness and the resources relied upon by the expert.
{¶ 2} David E. Valentine was employed by PPG Industries, Inc., from 1969 to 1997, and it is alleged that he was exposed to various toxic chemicals throughout his employment. In 1997, Mr. Valentine was diagnosed with glioblastoma multiforme, a form of brain cancer. As a result of the cancer, Mr. Valentine died in May 1999.
{¶ 3} Mr. Valentine’s widow, Linda Valentine, appellant, filed a claim for death benefits with the Bureau of Workers’ Compensation, alleging that her husband’s exposure to chemicals throughout his employment with PPG Industries caused the development of his cancer and his resulting death. The Industrial Commission denied the claim, and Valentine filed an administrative appeal in the Pickaway County Court of Common Pleas against appellee PPG Industries, Inc., the parent company of appellee PPG Industries Ohio, Inc.
{¶ 4} To establish that she qualified for workers’ compensation benefits, Valentine was required to prove that her husband’s illness was contracted in the course of his employment with PPG Industries. R.C. 4123.01(F); State ex rel. Ohio Bell Tel. Co. v. Krise (1975), 42 Ohio St.2d 247, 254, 71 O.O.2d 226, 327 N.E.2d 756. In an effort to establish that fact, Valentine presented expert testimony from two of her husband’s treating physicians, Dr. Michael E. Miner and Dr. Herbert B. Newton, and from an industrial hygienist, Norman Brusk.
[43]*43{¶ 5} Dr. Miner concluded that, based on a reasonable medical probability, Mr. Valentine’s brain tumor was directly and proximately caused by his exposure to chemical toxins in his workplace and that his death was directly caused by that exposure. Dr. Newton similarly opined that, based on a reasonable medical probability, the development of the tumor and ultimate death were directly and proximately related to Mr. Valentine’s chemical exposure. The doctors based their opinions on the totality of their experience as practitioners, their knowledge of Mr. Valentine’s condition and background, medical and genetic research, animal studies, and epidemiologic studies. Additionally, both doctors considered it significant that a former coworker of Mr. Valentine, Harold McConnaughey Jr., developed glioblastoma multiforme and died within two weeks of Mr. Valentine. Both doctors acknowledged that no chemical is known to cause glioblastoma multiforme and that ionizing radiation, which is not involved in this case, is the only proven cause of the disease.
{¶ 6} Mr. Brusk opined that Mr. Valentine’s employment with PPG Industries placed him at a heightened risk of developing brain cancer. Mr. Brusk based his opinion on his experience as an industrial hygienist, his assessment of Mr. Valentine’s workplace, and epidemiological studies. Mr. Brusk did not render a professional opinion regarding whether any specific chemical, or group of chemicals, is capable of causing glioblastoma multiforme.
{¶ 7} The trial court excluded the expert opinions as unreliable under Evid.R. 702(C). Because the expert testimony was inadmissible, the trial court found that Valentine was unable to establish causation and granted summary judgment for PPG Industries. The Fourth District Court of Appeals affirmed, holding that the trial court did not abuse its discretion when it excluded the expert testimony as unreliable.
{¶ 8} The matter is before this court upon the acceptance of a discretionary appeal.
{¶ 9} The determination of the admissibility of expert testimony is within the discretion of the trial court. Evid.R. 104(A). Such decisions will not be disturbed absent abuse of discretion. Miller v. Bike Athletic Co. (1998), 80 Ohio St.3d 607, 616, 687 N.E.2d 735. “Abuse of discretion” suggests unreasonableness, arbitrariness, or unconscionability. Without those elements, it is not the role of this court to substitute its judgment for that of the trial court. Calderon v. Sharkey (1982), 70 Ohio St.2d 218, 222, 24 O.O.3d 322, 436 N.E.2d 1008.
{¶ 10} Evid.R. 702 provides:
{¶ 11} “A witness may testify as an expert if all of the following apply:
[44]*44{¶ 12} “(A) The witness’ testimony either relates to matters beyond the knowledge or experience possessed by lay persons or dispels a misconception common among lay persons;
{¶ 13} “(B) The witness is qualified as an expert by specialized knowledge, skill, experience, training, or education regarding the subject matter of the testimony;
{¶ 14} “(C) The witness’ testimony is based on reliable scientific, technical, or other specialized information.”
{¶ 15} That the opinions related to matters beyond the knowledge and experience of laypersons is not disputed. See Evid.R. 702(A). Moreover, the credentials and experience of the witnesses clearly qualify them as experts under Evid.R. 702(B). In fact, the experience of Drs. Newton and Miner as Mr. Valentine’s personal physicians makes them uniquely qualified to discuss his health. The sole issue in this case, then, is whether the testimony in question is reliable under Evid.R. 702(C).
{¶ 16} In determining whether the opinion of an expert is reliable under Evid.R. 702(C), a trial court examines whether the expert’s conclusion is based on scientifically valid principles and methods. Miller, 80 Ohio St.3d 607, 687 N.E.2d 735, paragraph one of the syllabus. A court should not focus on whether the expert opinion is correct or whether the testimony satisfies the proponent’s burden of proof at trial. Id. Accordingly, we are not concerned with the substance of the experts’ conclusions; our focus is on how the experts arrived at their conclusions.
{¶ 17} The qualification and reliability requirements of Evid.R. 702 are distinct. Because even a qualified expert is capable of rendering scientifically unreliable testimony, it is imperative for a trial court, as gatekeeper, to examine the principles and methodology that underlie an expert’s opinion. Cf. Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993), 509 U.S. 579, 589, 113 S.Ct. 2786, 125 L.Ed.2d 469 (“under [Fed.R.Evid. 702] the trial judge must ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable”); Gen. Elec. Co. v. Joiner (1997), 522 U.S. 136, 142, 118 S.Ct. 512, 139 L.Ed.2d 508 (discussing the gatekeeping role of the trial judge under Fed.R.Evid. 702). It is that determination that ensures that the testimony will be helpful to the trier of fact.
{¶ 18} Experts often base their opinions on data and research from within their field of study. Evid.R.
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Moyer, C.J.
{¶ 1} The question presented in this appeal is whether Evid.R. 702(C) requires a scientifically valid connection between the opinion of an expert witness and the resources relied upon by the expert.
{¶ 2} David E. Valentine was employed by PPG Industries, Inc., from 1969 to 1997, and it is alleged that he was exposed to various toxic chemicals throughout his employment. In 1997, Mr. Valentine was diagnosed with glioblastoma multiforme, a form of brain cancer. As a result of the cancer, Mr. Valentine died in May 1999.
{¶ 3} Mr. Valentine’s widow, Linda Valentine, appellant, filed a claim for death benefits with the Bureau of Workers’ Compensation, alleging that her husband’s exposure to chemicals throughout his employment with PPG Industries caused the development of his cancer and his resulting death. The Industrial Commission denied the claim, and Valentine filed an administrative appeal in the Pickaway County Court of Common Pleas against appellee PPG Industries, Inc., the parent company of appellee PPG Industries Ohio, Inc.
{¶ 4} To establish that she qualified for workers’ compensation benefits, Valentine was required to prove that her husband’s illness was contracted in the course of his employment with PPG Industries. R.C. 4123.01(F); State ex rel. Ohio Bell Tel. Co. v. Krise (1975), 42 Ohio St.2d 247, 254, 71 O.O.2d 226, 327 N.E.2d 756. In an effort to establish that fact, Valentine presented expert testimony from two of her husband’s treating physicians, Dr. Michael E. Miner and Dr. Herbert B. Newton, and from an industrial hygienist, Norman Brusk.
[43]*43{¶ 5} Dr. Miner concluded that, based on a reasonable medical probability, Mr. Valentine’s brain tumor was directly and proximately caused by his exposure to chemical toxins in his workplace and that his death was directly caused by that exposure. Dr. Newton similarly opined that, based on a reasonable medical probability, the development of the tumor and ultimate death were directly and proximately related to Mr. Valentine’s chemical exposure. The doctors based their opinions on the totality of their experience as practitioners, their knowledge of Mr. Valentine’s condition and background, medical and genetic research, animal studies, and epidemiologic studies. Additionally, both doctors considered it significant that a former coworker of Mr. Valentine, Harold McConnaughey Jr., developed glioblastoma multiforme and died within two weeks of Mr. Valentine. Both doctors acknowledged that no chemical is known to cause glioblastoma multiforme and that ionizing radiation, which is not involved in this case, is the only proven cause of the disease.
{¶ 6} Mr. Brusk opined that Mr. Valentine’s employment with PPG Industries placed him at a heightened risk of developing brain cancer. Mr. Brusk based his opinion on his experience as an industrial hygienist, his assessment of Mr. Valentine’s workplace, and epidemiological studies. Mr. Brusk did not render a professional opinion regarding whether any specific chemical, or group of chemicals, is capable of causing glioblastoma multiforme.
{¶ 7} The trial court excluded the expert opinions as unreliable under Evid.R. 702(C). Because the expert testimony was inadmissible, the trial court found that Valentine was unable to establish causation and granted summary judgment for PPG Industries. The Fourth District Court of Appeals affirmed, holding that the trial court did not abuse its discretion when it excluded the expert testimony as unreliable.
{¶ 8} The matter is before this court upon the acceptance of a discretionary appeal.
{¶ 9} The determination of the admissibility of expert testimony is within the discretion of the trial court. Evid.R. 104(A). Such decisions will not be disturbed absent abuse of discretion. Miller v. Bike Athletic Co. (1998), 80 Ohio St.3d 607, 616, 687 N.E.2d 735. “Abuse of discretion” suggests unreasonableness, arbitrariness, or unconscionability. Without those elements, it is not the role of this court to substitute its judgment for that of the trial court. Calderon v. Sharkey (1982), 70 Ohio St.2d 218, 222, 24 O.O.3d 322, 436 N.E.2d 1008.
{¶ 10} Evid.R. 702 provides:
{¶ 11} “A witness may testify as an expert if all of the following apply:
[44]*44{¶ 12} “(A) The witness’ testimony either relates to matters beyond the knowledge or experience possessed by lay persons or dispels a misconception common among lay persons;
{¶ 13} “(B) The witness is qualified as an expert by specialized knowledge, skill, experience, training, or education regarding the subject matter of the testimony;
{¶ 14} “(C) The witness’ testimony is based on reliable scientific, technical, or other specialized information.”
{¶ 15} That the opinions related to matters beyond the knowledge and experience of laypersons is not disputed. See Evid.R. 702(A). Moreover, the credentials and experience of the witnesses clearly qualify them as experts under Evid.R. 702(B). In fact, the experience of Drs. Newton and Miner as Mr. Valentine’s personal physicians makes them uniquely qualified to discuss his health. The sole issue in this case, then, is whether the testimony in question is reliable under Evid.R. 702(C).
{¶ 16} In determining whether the opinion of an expert is reliable under Evid.R. 702(C), a trial court examines whether the expert’s conclusion is based on scientifically valid principles and methods. Miller, 80 Ohio St.3d 607, 687 N.E.2d 735, paragraph one of the syllabus. A court should not focus on whether the expert opinion is correct or whether the testimony satisfies the proponent’s burden of proof at trial. Id. Accordingly, we are not concerned with the substance of the experts’ conclusions; our focus is on how the experts arrived at their conclusions.
{¶ 17} The qualification and reliability requirements of Evid.R. 702 are distinct. Because even a qualified expert is capable of rendering scientifically unreliable testimony, it is imperative for a trial court, as gatekeeper, to examine the principles and methodology that underlie an expert’s opinion. Cf. Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993), 509 U.S. 579, 589, 113 S.Ct. 2786, 125 L.Ed.2d 469 (“under [Fed.R.Evid. 702] the trial judge must ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable”); Gen. Elec. Co. v. Joiner (1997), 522 U.S. 136, 142, 118 S.Ct. 512, 139 L.Ed.2d 508 (discussing the gatekeeping role of the trial judge under Fed.R.Evid. 702). It is that determination that ensures that the testimony will be helpful to the trier of fact.
{¶ 18} Experts often base their opinions on data and research from within their field of study. Evid.R. 702(C) requires not only that those underlying resources are scientifically valid, but also that they support the opinion. Although scientists certainly may draw inferences from a body of work, trial courts must ensure that any such extrapolation accords with scientific principles and methods. In this respect, we find persuasive Gen. Elec. Co. v. Joiner. In Joiner, the United [45]*45States Supreme Court, in discussing the reliability requirements of Fed.R.Evid. 702, stated, “A court may conclude that there is simply too great an analytical gap between the data and the opinion proffered.” Gen. Elec. Co. v. Joiner, 522 U.S. at 146, 118 S.Ct. 512, 139 L.Ed.2d 508. Because expert opinion based on nebulous methodology is unhelpful to the trier of fact, it has no place in courts of law.
{¶ 19} Valentine asserts that this conclusion invades the province of the jury. This argument demonstrates a fundamental misunderstanding of the purpose and operation of Evid.R. 702. A decision not to admit expert evidence under Evid.R. 702 does not invade the province of the jury. Instead, such a decision prevents the jury from considering information that would not assist in rendering a verdict founded on reliable expert evidence.
{¶ 20} Valentine also asks us to impose an affirmative duty on a trial court to acquaint itself with the scientific literature that underlies an expert’s opinion. The abuse-of-discretion standard, which applies to admissibility determinations, already targets the potential problem that this proposal attempts to avoid. To the extent that doing so is necessary to avoid making an unreasonable, arbitrary, or unconscionable decision, a trial court is obliged to apprise itself of the details of proffered evidence. There is no indication that the trial court failed to do so in this case.
{¶ 21} The trial court concluded that the proffered opinions were not based on reliable scientific methodology, finding that the underlying conclusion of the experts’ opinions (i.e., that the chemicals to which Mr. Valentine was exposed are capable of causing glioblastoma multiforme) was not scientifically reliable. None of the experts’ opinions cited any studies showing a causal connection between chemical exposure and glioblastoma multiforme. The epidemiological studies did not involve persons in the same industry in which Valentine worked and did not identify a particular chemical or group of chemicals that cause glioblastoma multiforme. Similarly, the animal studies cited did not indicate that brain tumors develop across species. Moreover, the fact that a number of the chemicals to which Mr. Valentine was exposed have been classified as carcinogens does not establish that they are capable, individually or collectively, of causing glioblastoma multiforme. To arrive at their opinions, the experts were required to extrapolate from the conclusions of the underlying materials. The trial court did not abuse its discretion in finding that the experts did not adequately explain the scientific basis for doing so.
{¶ 22} The experts relied heavily on differential diagnosis to reach their conclusions. “Differential diagnosis” describes the process of isolating the cause of a patient’s symptoms through the systematic elimination of all potential causes. See Hardyman v. Norfolk & W. Ry. Co. (C.A.6, 2001), 243 F.3d 255, 260, quoting [46]*46Federal Judicial Center, Reference Manual on Scientific Evidence (1994) 214. Although differential diagnosis is a standard scientific method for determining causation, see Westberry v. Gislaved Gummi AB (C.A.4, 1999), 178 F.3d 257, 262, its use is appropriate only when considering potential causes that are scientifically known. For example, in Westberry, the plaintiff alleged that breathing airborne talc caused aggravation of a preexisting sinus condition. Because the parties did not dispute that inhalation of high levels of talc causes irritation in mucous membranes, differential diagnosis was a valid method to establish causation. Id. at 264-265. In contrast, Drs. Newton and Miner were unable to establish that any of the chemicals to which Mr. Valentine was exposed are capable of causing glioblastoma multiforme. Accordingly, differential diagnosis is not a reliable method for determining legal causation in this case.
{¶ 23} Although the experts are highly qualified, their experience, by itself, does not establish the legal reliability of their opinions as applied to the facts of this case. Nor does the contemporaneous death of Mr. Valentine’s coworker, Harold McConnaughey, demonstrate reliability. “When an unusual event follows closely on the heels of another unusual event, the ordinary person infers a causal relation * * *. But lay speculations on medical causality, however plausible, are a perilous basis for inferring causality.” Rosen v. Ciba-Geigy Corp. (C.A.7, 1996), 78 F.3d 316, 318. “[T]he courtroom is not the place for scientific guesswork, even of the inspired sort. Law lags science; it does not lead it.” Id. at 319. Expert opinion based on unscientific principles and methodology is unhelpful to the trier of fact and has no place in courts of law. Accordingly, the trial court did not abuse its discretion when it excluded the expert testimony proffered by Valentine.
Judgment affirmed.
O’Connor, O’Donnell and Lanzinger, JJ., concur.
Resnick, Pfeifer and Lundberg Stratton, JJ., dissent.