Full opinion text
DENNIS, Circuit Judge: In this negligence case, we are called upon to determine the standards for assessing the reliability of the proffer of a clinical physician’s expert opinion as to the cause of a plaintiffs disease in the light of Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993). We conclude that: (1) the basic principles of the Federal Rules of Evidence recognized by Daubert apply to the admission or exclusion of every type of expert testimony; (2) a trial judge, therefore, must assess every proffer of expert testimony to determine whether it is relevant to the case and reliable under the principles and methodology of the discipline involved; (3) the Supreme Court in Daubert interpreted “scientific knowledge” under Federal Rule of Evidence 702 to mean knowledge obtained and tested by the scientific method, i.e. “hard” or “Newtonian” scientific knowledge; (4) accordingly, the Daubert Court indicated that a trial court should assess the reliability of expert testimony professedly based on “hard” scientific knowledge using several factors, the “Daubert factors,” which are “hard” science methods or techniques; (5) clinical medicine (as opposed to research and laboratory medical science) is not a hard science discipline; its goals, subject matter, conditions of study and well developed methodology are sui generis and quite different from that of hard science and its methodology; (6) consequently, a trial judge assessing the reliability of the proffer of a clinical physician’s expert testimony based on clinical medical knowledge should determine whether it is soundly grounded in the knowledge, principles and methodology of clinical medicine; the “Daubert factors,” which are techniques derived from hard science methodology, are, as a general rule, inappropriate for use in making the reliability assessment of expert clinical medical testimony. The foregoing conclusions are the results of our conscientious efforts to determine the standard for admitting clinical medical testimony under the Federal Rules of Evidence as interpreted by the Supreme Court in Daubert and by this court in Watkins v. Telsmith, Inc., 121 F.3d 984 (5th Cir.1997) and other authorities cited herein. They represent neither a “let it all in” nor a “keep it all out” view. Instead, they reflect the interplay of the basic principles of the Federal Rules of Evidence, viz., the liberal standards of admissibility and relevance of Rules 401 and 402 and the assumption underlying Rules 702 and 703 “that the expert’s opinion will have a rehable basis in the knowledge and experience of his discipline.” Daubert, 509 U.S. at 587, 592, 113 S.Ct. at 2793, 2796. I. Introduction Plaintiffs-appellants, Bob T. Moore and his wife, Susan Moore, filed this suit against the defendants-appellees in Texas state court, alleging that Moore had contracted reactive airways disease as the result of the defendants-appellees’ negligence in causing Moore to be exposed to a mixture of chemical gases on their premises. Defendants-appellees removed the suit to federal court on diversity grounds. Before trial the plaintiffs proffered the testimony of two well credentialed clinical physician experts, Dr. Daniel Jenkins and Dr. Antonio Alvarez, who expressed identical opinions based on clinical medical methodology that Bob T. Moore suffered from reactive airways disease that had been caused by his inhalation of the mixture of chemical gases on defendants-appellees’ premises. Dr. Jenkins based his opinion on his firsthand observations in examining and taking a history from Bob T. Moore, on the results of tests he performed or had performed on Moore, and on facts and data he obtained from other physicians who had previously examined, tested and treated Moore. Dr. Alvarez essentially adopted the facts, data and conclusions developed and compiled by Dr. Jenkins. To confirm his opinion before the proffer, Dr. Jenkins reviewed and considered reports he received of Dr. Alvarez’s subsequent treatment and allergy testing of Bob T. Moore. In response, the defendants-appellees moved to exclude the testimony of Dr. Jenkins and Dr. Alvarez on the grounds that the proffers failed to demonstrate reliable bases for their opinions. The trial court concluded that the proffer of Dr. Jenkins’ testimony demonstrated a reliable basis for his diagnosis of Moore’s reactive airways disease. However, the court excluded Dr. Jenkins’ opinion that Moore’s exposure to the chemicals caused the disease on dual grounds, viz., (1) that under Federal Rule of Evidence 702 the opinion did not have a reliable basis, and (2) that under Federal Rule of Evidence 403 the probative value of the opinion was outweighed by the prejudice that would be caused by Dr. Jenkins’ highly impressive qualifications. The trial court admitted Dr. Alvarez’s opinions as to both diagnosis and cause of disease as evidentiarily reliable, despite the fact that Dr. Alvarez relied heavily on Dr. Jenkins’ opinion and based his own opinion essentially on the same data that had been developed and used by Dr. Jenkins. At the jury trial, Dr. Jenkins’ testimony was limited to his diagnosis of Moore’s disease and did not touch on causation. Dr. Alvarez testified as to both the diagnosis and the cause of the disease. Dr. Alvarez, however, was forced to admit that in forming his opinions he relied heavily on the work and opinions of Dr. Jenkins. Dr. Alvarez was unable to explain possible discrepancies in the data he used that had been compiled by Dr. Jenkins. Counsel for the defendantsappellees in closing argument pointed out that Dr. Alvarez was not as highly qualified as their medical causation expert who testified that Moore’s disease had not been caused by exposure to the mixture of chemicals. The jury answered “No” to an interrogatory asking whether the negligence, if any, of the defendants-appellees had proximately caused the injury in question. The district court entered a take nothing judgment against the plaintiffs. The plaintiffs appealed, assigning as error the trial court’s ruling that excluded Dr. Jenkins’ testimony as to his opinion or inference that Moore’s disease had been caused by his exposure to the chemicals he encountered at the defendantappellees’ facility. II. Daubert’s Illumination and Impact The trial court’s oral ruling excluded Dr. Jenkins’ opinion as to cause of disease under Rules 702 and 403, apparently based on the court’s understanding of the Rules as interpreted and impacted by the Supreme Court’s decision in Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993). Therefore, before analyzing the trial court’s interpretation ,and application of the law to the particular proffer of expert testimony, we will set forth our reading of the essential elements of the pertinent Federal Rules of Evidence that have been illumined and impacted by Daubert. A. Rule 702 Rule 702 provides that: 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 by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise. In admitting expert testimony, Rule 702 requires that two preliminary determinations be made by the trial court. First, the proffered witness must be qualified as an expert by knowledge, skill, experience, training, or education. Second, the proffered expert’s opinion, inference or other testimony must be based on scientific, technical or other specialized knowledge that will assist the trier of fact to understand the evidence or determine a fact in issue. To facilitate discussion, we refer to these as the “qualifications” and “knowledge” components of Rule 702. 1. Qualifications An expert must have scientific, technical or other specialized knowledge, and a witness may be qualified as an expert by reason of knowledge, skill, experience, training or education. Fed.R.Evid. 702; Christophersen v. Allied-Signal Corp., 939 F.2d 1106, 1110 (5th Cir.1991)(ere banc). Rule 702, according to the Advisory Committee Note, permits expert testimony not only by experts carrying formal credentials such as university degrees and professional memberships but also by so-called skilled witnesses, whose experiences permit them to testify with authority on a given topic. Id. The areas of inquiry that expert testimony may address are similarly broad, including scientific and technical questions as well as any other areas of specialized knowledge. Id. The question of whether the witness is sufficiently qualified as an expert is a matter to be decided by the court pursuant to Rule 104(a). United States v. Normile, 587 F.2d 784 (5th Cir.1978); Loftin & Woodard, Inc. v. United States, 577 F.2d 1206 (5th Cir.1978). In making this inquiry, the trial court has wide discretion in determining the qualifications of a witness as an expert with respect to a particular subject. Hamling v. United States, 418 U.S. 87, 108, 94 S.Ct. 2887, 2902, 41 L.Ed.2d 590 (1974), reh’g denied, 419 U.S. 885, 95 S.Ct. 157, 42 L.Ed.2d 129 (1974); Robert v. Conti Carriers & Terminals, Inc. 692 F.2d 22 (5th Cir.1982). In Daubert, the question of an expert’s qualification under Rule 702 was not raised. The court stated that the experts were well or impressively credentialed. Daubert, 509 U.S. at 582-583, 113 S.Ct. at 2791-92. Accordingly, Daubert does not affect the foregoing principles pertaining to qualifications. 2. Knowledge In Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993), the Supreme Court was called upon to determine the standard for admitting expert scientific testimony in a federal trial. Id. at 582, 113 S.Ct. at 2791. The court had granted certiorari in light of sharp divisions among courts applying and rejecting the test of Frye v. United States, 54 App.D.C. 46, 47, 293 F. 1013, 1014 (D.C.Cir.1923) that expert opinion based on a scientific technique is inadmissible unless the technique is “generally accepted” as reliable in the relevant scientific community. Daubert, 509 U.S. at 585, 113 S.Ct. at 2792. The court held that the Frye “general acceptance” test had been displaced by the Federal Rules of Evidence, observing that: Rule 702 specifically governing expert testimony does not establish “general acceptance” as an absolute prerequisite to admissibility; the drafting history of the rule does not indicate an intention to incorporate such a standard; and a rigid “general acceptance” standard would be at odds with the liberal thrust of the Federal Rules and their general approach of relaxing the traditional barriers to opinion testimony. Id. at 588-589, 113 S.Ct. at 2794-2795. The Supreme Court also held that the Federal Rules require the trial judge to ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable. Id. at 589, 113 S.Ct. at 2794. Citing Rule 702 as the primary locus of this obligation, the court decided that the trial judge, when faced with a proffer of expert scientific testimony, must determine pursuant to Rule 104(a) whether the expert is proposing to testify to (1) scientific knowledge that (2) will assist the trier of fact to understand or determine a fact in issue. The court explained that this entails a preliminary assessment of whether the underlying reasoning of the scientific testimony is soundly grounded in scientific knowledge and methodology and can be relevantly applied to the facts in issue. Id. at 592, 113 S.Ct. at 2796. a. Hard Scientific Knowledge Speaking specifically of “scientific knowledge,” the Court stated that the adjective “ ‘scientific’ implies a grounding in the methods and procedures of science.” Id. The Court elaborated: “‘Science is not an encyclopedic body of knowledge about the universe. Instead, it represents a process for proposing and refining theoretical explanations about the world that are subject to further testing and refinement____’ But, in order to qualify as ‘scientific knowledge,’ an inference or assertion must be derived by the scientific method. Proposed testimony must be supported by appropriate validation — i.e., ‘good grounds,’ based on what is known. In short, the requirement that an expert’s testimony pertain to ‘scientific knowledge’ establishes a standard of evidentiary reliability.” Id. quoting from Brief for American Association for the Advancement of Science et al. as Amici Curiae 7-8. (Parentheses omitted; emphasis in original). Thus, the Daubert Court defined “scientific knowledge” in terms of “hard science” or “Newtonian science” i.e., knowledge obtained and tested through “the scientific method,” of which Sir Issac Newton was the leading exponent. See Edward J. Imwinkelried, The Next Step After Daubert, Developing A Similarly Epistemological Approach To Ensuring The Reliability of Nonscientific Expert Testimony, 15 Cardozo L.Rev. 2271, 2276-2277 (1994)(citing 5 The Encyclopedia of Philosophy 490-491 (Paul Edwards ed., 1967)); Jennifer Laser, Comment, Inconsistent Gatekeeping in Federal Courts: Application of Daubert v. Merrell Dow Pharmaceuticals, Inc. to Nonscientific Expert Testimony, 30 Loy. L.A.L.Rev. 1379, 1404 (1997); United States v. Hall, -F.Supp. -, - (C.D.Ill.1997); United States v. Starzecpyzel, 880 F.Supp. 1027, 1039 (S.D.N.Y.1995). The methodology of hard or Newtonian science is what distinguishes it from other fields of human inquiry. See Michael D. Green, Expert Witnesses and Sufficiency of Evidence in Toxic Substances Litigation: The Legacy of Agent Orange and Bendectin Litigation, 86 Nw.U.L.Rev. 643, 645 (1992). “Scientific methodology today is based on generating hypotheses and testing them to see if they can be falsified.... Theoretically, therefore, hypotheses are not affirmatively proved, only falsified. Of course, if a hypothesis repeatedly withstands falsification, one may tend to accept it even if conditionally true.” Id. at 645-646 (citing Karl R. Popper, The Logic of Scientific Discovery (1965); David L. Faigman, To Have and Have Not: Assessing the Value of Social Science to the Law as Science and Policy, 38 Emory L.J. 1005,1015-17(1989); Interdisciplinary Panel on Carcinogenicity, Criteria for Evidence of Chemical Carcinogenicity, 225 Sci. 682, 683 (1984)). b. Knowledge Outside the Realm of Hard Science In Daubert the Supreme Court noted that, although Rule 702 also applies to “technical, or other specialized knowledge,” its discussion was “limited to the scientific context because that is the nature of the expertise offered here.” Id. at 590 n. 8, 113 S.Ct. at 2795 n. 8. Nevertheless, we conclude that, except where it is • self-evident that the court’s remarks specifically apply only to “scientific knowledge,” that the general principles of Rule 702 recognized by the decision are applicable to other species of expert testimony. Moreover, in Watkins v. Telsmith, 121 F.3d 984, 991 (5th Cir.1997), another panel of this court recently concluded that “whether an expert’s testimony is based on ‘scientific, technical or other specialized knowledge,’ Daubert and Rule 702 demand that the district court evaluate the methods, analysis, and principles relied upon in reaching the opinion.” The Daubert court began by stating that “[w]e interpret the legislatively-enacted Federal Rules of Evidence as we would any statute.” Id. at 587, 113 S.Ct. at 2793(citing Beech Aircraft Corp. v. Rainey, 488 U.S. 153, 163, 109 S.Ct. 439, 446, 102 L.Ed.2d 445 (1988))(“Because the Federal Rules of Evidence are a legislative enactment, courts turn to the ‘traditional tools of statutory construction in order to construe their provisions.’ ”) Accordingly, a court must not be guided by a single sentence or member of a sentence, but look to the provisions of the whole law, and to its object and policy. United States Nat. Bank of Or. v. Independent Ins. Agents of America, 508 U.S. 439, 455, 113 S.Ct. 2173, 2182, 124 L.Ed.2d 402 (1993)(citing United States v. Heirs of Boisdore, 49 U.S. (8 How.) 113, 122, 12 L.Ed. 1009 (1849)). A statutory text consists of words living a communal existence, the meaning of each word informing the others and all taking their purport from their context. Id. at 454, 113 S.Ct. at 2182 (citing NLRB v. Federbush, Co., 121 F.2d 954, 957 (2nd Cir.1941)(L.Hand, J.)). The maxim noscitur a sociis, that a word is known by the company it keeps, is often used to avoid giving one word a scope inconsistent with its companions and thus giving “ ‘unintended breadth to the Acts of Congress.’” Gustafson v. Alloyd Co., 513 U.S. 561, 575, 115 S.Ct. 1061, 1069, 131 L.Ed.2d 1 (1995)(citing and quoting Jarecki v. G.D. Searle & Co., 367 U.S. 303, 307, 81 S.Ct. 1579, 1582, 6 L.Ed.2d 859 (1961)). Consequently, the requirements that Daubert found to be inherent in Rule 702, viz., that the trial judge must ensure that the expert’s evidence is not only relevant, but reliable, must be applicable to “technical, or other specialized knowledge,” as well as to scientific testimony. Otherwise, Rule 702 would not place limits on the admissibility of non-scientific expert testimony comparable to those it imposes on purportedly scientific evidence. Moreover, the Daubert opinion at several points clearly implies that it is drawing on principles of the Federal Rules that are generally applicable to all types of expert testimony. The court stated that “Rule 702 ... clearly contemplates some degree of regulation of the subjects and theories about which an expert may testify.” Daubert, 509 U.S. at 589, 113 S.Ct. at 2794. Further, the court observed that the premise for the relaxation of the usual requirement of firsthand knowledge when any type of qualified expert testifies is “an assumption that the expert’s opinion will have a reliable basis in the knowledge and experience of his discipline.” Id. at 592, 113 S.Ct. at 2796 Thus, Daubert plainly indicates that the trial judge, when faced with the proffer of expert testimony in any field of study, must determine whether the reasoning or methodology underlying the testimony is valid under the principles of the discipline involved. Id.; See American College of Trial Lawyers, Standards And Procedures For Determining The Admissibility Of Expert Evidence After Daubert, 157 F.R.D. 571, 578 (1994). c. Reliability: The expert’s opinion or inference must be grounded in the methodology of his discipline. The Daubert court read Rule 702 to provide that “ ‘[i]f scientific technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue’ ” an expert “ ‘may testify thereto.’” Daubert, 509 U.S. at 589, 113 S.Ct. at 2794 (emphasis by Court deleted). “Knowledge” in this context “ ‘applies to any body of known facts or to any body of ideas inferred from such facts or accepted as truths on good grounds.’ ” Id. at 590, 113 S.Ct. at 2795(quoting Webster’s Third New International Dictionary 1252 (1986)). In Daubert, the Court indicated that, (1) “scientific knowledge” within Rule 702 means principles, theories, techniques or inferences derived by the scientific method or by a body of sound scientific methods; and (2) that the proffered expert’s opinion, inference, or testimony based on scientific knowledge, in order to have evidentiary reliability or trustworthiness, must be derived or inferred by the same methods. Id. at 590 n. 9, 113 S.Ct. at 2795; See also the court’s “general observations” on principal scientific methods. Id. at 593-594, 113 S.Ct. at 2796-2797. By the same token, we conclude that, under Rule 702, an opinion based on other technical or specialized knowledge, must be grounded in the principles, methods and procedures of the particular field of knowledge involved. Every discipline employs a body of methods, rules, and postulates, i.e., methodology, both in its ordinary functions and in developing and adopting new concepts, techniques, and analogues. Therefore, the “knowledge” of each discipline, under Rule 702, is both its principles and methodology and the theories, techniques or inferences produced through its methodology. Thus, the proffered opinion of any expert in a field of knowledge, in order to be evidentiarily reliable, must either be based soundly on the current knowledge, principles and methodology of the expert’s discipline or be soundly inferred or derived therefrom. As the American College of Trial Lawyers’ report concludes, “[WJhether the testimony concerns economic principles, accounting standards, property valuation or other nonseientifie subjects, it should be evaluated by reference to the ‘knowledge and experience’ of that particular field. To that extent, Daubert ought to be regarded as universally applicable to expert evidence.” American College of Trial Lawyers, Standards and Procedures for Determining the Admissibility of Expert Evidence after Daubert, 157 F.R.D. 571, 579 (1994). For the same reasons, this court recently held in Watkins v. Telsmith, Inc., 121 F.3d 984 (5th Cir.1997) that the application of Daubert in determining the admissibility of expert testimony is not limited to “scientific knowledge” or “novel” scientific evidence. Id. at 989-991. Moreover, in Watkins, this court concluded that: [Wjhether an expert’s testimony is based on “scientific, technical or other specialized knowledge,” Daubert and Rule 702 demand that the district court evaluate the methods, analysis, and principles relied upon in reaching the opinion. The court should ensure that the opinion comports with applicable professional standards outside the courtroom and that it “will have a reliable basis in the knowledge and experience of [the] discipline.” Id. at 991(quoting Daubert, 509 U.S. at 592, 113 S.Ct. at 2796.) (also citing and quoting Cummins v. Lyle Indus., 93 F.3d 362, 366-371 (7th Cir.1996)(Rule 702 demands that experts “adhere to the same standards of intellectual rigor that are demanded in their professional work.” Id. at 369)(citing Rosen v. Ciba-Geigy Corp., 78 F.3d 316, 318 (7th Cir.1996))); See also Tyus v. Urban Search Management, 102 F.3d 256, 263 (7th Cir.1996)(“Social science testimony ... must be tested to be sure that the person possesses genuine expertise in a field and that her court testimony ‘adheres to the same standards of intellectual rigor that are demanded in [her] professional work.’ ”)(quoting Braun v. Lorillard Inc., 84 F.3d 230, 234 (7th Cir.1996)). d. Relevance: The opinion or inference must be relevant to the case. Rule 702 further requires that the evidence or testimony “assist the trier of fact to understand the evidence or to determine a fact in issue.” This condition goes primarily to relevance. Daubert, 509 U.S. at 590, 113 S.Ct. at 2795. “‘Expert testimony which does not relate to any issue in the case is not relevant and, ergo, non-helpful.’ 3 Weinstein & Berger ¶ 702[02], p. 702-18. See also United States v. Downing, 753 F.2d 1224, 1242 (3d Cir.1985)(‘An additional consideration under Rule 702—and another aspect of relevancy—-is whether expert testimony proffered in the case is sufficiently tied to the facts of the case that it will aid the jury in resolving a factual dispute’). ” Id. at 591, 113 S.Ct. at 2795. “The study of the phases of the moon, for example, may provide valid scientific ‘knowledge’ about whether a certain night was dark, and if darkness is a fact in issue, the knowledge will assist the trier of fact. However (absent creditable grounds supporting such a link), evidence that the moon was full on a certain night will not assist the trier of fact in determining whether an individual was unusually likely to have behaved irrationally on that night.” Id. e. The trial judge is the gatekeeper. Accordingly, when faced with a proffer of a qualified expert’s testimony to scientific, technical or other specialized knowledge, the trial judge must determine at the outset, pursuant to Rule 104(a), whether the proffered opinion or inference is soundly grounded in the methodology of the expert’s discipline and whether that opinion or inference is relevant to a fact in issue or to an understanding of the evidence. Cf. Daubert, 509 U.S. at 589-592, 113 S.Ct. at 2794-2796. The Court emphasized that the trial judge’s inquiry under Rule 702 is a flexible one. Different approaches may be permissible, but the focus must be on the principles and methodology upon which the expert’s opinion is based, not on the merits of the expert’s conclusion. Id. at 594-595 n. 12, 113 S.Ct. at 2797-2798. “Vigorous 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.” Id. at 596, 113 S.Ct. at 2798 (citing Rock v. Arkansas, 483 U.S. 44, 61, 107 S.Ct. 2704, 2714, 97 L.Ed.2d 37 (1987)). “Additionally, in the event the trial court concludes that the scintilla of evidence presented supporting a position is insufficient to allow a reasonable juror to conclude that the position more likely than not is true, the court remains free to direct a judgment, Fed. Rule Civ. Proc. 50(a), and likewise to grant summary judgment, Fed. Rule Civ. Proc. 56.” Id. (citing cf., e.g., Turpin v. Merrell Dow Pharmaceuticals, Inc., 959 F.2d 1349 (6th Cir.), cert. denied, 506 U.S. 826, 113 S.Ct. 84, 121 L.Ed.2d 47 (1992); Brock v. Merrell Dow Pharmaceuticals, Inc., 874 F.2d 307 (5th Cir.1989), modified, 884 F.2d 166 (5th Cir.1989), cert. denied, 494 U.S. 1046, 110 S.Ct. 1511, 108 L.Ed.2d 646 (1990)). f. The Daubert “factors” are hard scientific methods that generally are inappropriate for the reliability assessment of clinical medical testimony. After declaring that evidentiary reliability of an expert’s scientific opinion depends on whether it is soundly grounded in the the scientific method, the Daubert Court identified several individual methods or techniques within the body of hard or Newtonian scientific methodology as appropriate for trial judges’ use in testing the methodology-relatedness of particular hard scientific opinion proffers. Daubert, 509 U.S. at 593, 113 S.Ct. at 2796. These hard scientific methods, now sometimes called “Daubert factors,” are empirical testing, peer review and publication, known or potential rate of error, the existence and maintenance of operational standards, and acceptance within a relevant scientific community. Id. at 593-94, 113 S.Ct. at 2796-2797. Because the objectives, functions, subject matter and methodology of hard science vary significantly from those of the discipline of clinical medicine, as distinguished from research or laboratory medicine, the hard science techniques or methods that became the “Daubert factors” generally are not appropriate for assessing the evidentiary reliability of a proffer of expert clinical medical testimony. First, the goals of the disciplines of clinical medicine and hard or Newtonian science are different. In hard science, the usual motive is inquiring: to gain a new understanding of some mechanism of nature. Alvan R. Feinstein, Clinical Judgment 22 (1967) [hereinafter Feinstein]. In contrast, the care and treatment of the individual patient is the ultimate, specific act that characterizes a clinical physician. Id. at 27; Pellegrino and Thomasma, For The Patient’s Good 71 (1988); Pellegrino and Thomasma, A Philosophical Basis of Medical Practice 120 (1981)(“[T]he whole process is ordained to a specific practical end — a right action for a particular patient — and ... this end must modulate each step leading to it in important ways.”). The clinical physician, therefore, must take account of the immediacy of the problem confronting her for she bears an essential relationship to each patient. Additionally, she has many human values to consider — ethics, compassion, and must have a willingness to take responsibility in the face of the unknown. Edmond A. Murphy, The Logic of Medicine 6 (1976)[hereinafter Murphy], The pursuit of these different goals of hard science and clinical medicine serves to shape the distinct objectives of the scientific experiment and the clinical treatment of a patient: In clinical treatment, the main motives are remedial, or prophylactic: to change what nature has done or to prevent what it may do. In laboratory work, the premise is innovative: the goal is to test a new hypothesis or a new procedure. In ordinary clinical treatment, the premise is repetitive: the goal is to reproduce (or surpass) the best results of experiments conducted before in similar circumstances. A clinician chooses treatment in a new situation by reviewing what was done and what happened in previous situations that resembled the one at hand; he then selects whatever mode of treatment had the most successful outcome in the past. Id. at 22. In ordinary clinical treatment, the purpose is not to gain new knowledge but to repeat a success of the past. Id. at 23. Second, the subject matter and conditions of study are different. “In laboratory work, the experimental material is an intact animal, a part of a person or of an animal, or an inanimate system; in clinical treatment, the material is an intact human being.” Id. at 22. The hard scientist initiates the experiment at a time of his own convenience and chooses the material usually without regard to its desire or consent for participation. Id. In clinical medicine, the patient initiates the treatment, choosing the time, place, duration, and clinician. Id. “The physician is not studying the properties of chemical compounds in a test tube; he cannot postpone dealing with cancer in a patient for fifty years because he hopes by then to have a much clearer insight into the nature of the disorder.” Id. Finally, clinical medicine and hard science have markedly different methodologies. A clinician observes at least three types of data for each patient who undergoes treatment: A disease in morphologic, chemical, microbiologie, physiologic, or other impersonal terms; the host in whom the disease occurs and his environmental background, including his personal properties (such as age, race, sex, and education) and external surroundings (such as geographic location, occupation, and financial and social status) before the disease began; and the illness that occurs in the interaction between the disease and its environmental host, consisting of clinical phenomena: the host’s subjective sensations, or “symptoms,” and “signs,” which are findings discerned objectively during the physical examination. Feinstein, at 24-25. Using these data, the clinician determines a present diagnosis (which gives the disease a name and tells what is wrong), a past etiology and pathogenesis (or how it got that way), and a future prognosis and therapy (or what to do about it). Id. at 25. Some of the data used by the clinician can often be obtained by examining the patient’s fluids, cells, tissues, excreta, roentgenograms, graphic tracings, and other derivative substances. The patient’s personal environmental data can often be elicited by nurses, secretaries, social workers, or other interviewers. But the history-taking, physical examination, and the determination of symptoms and signs can properly be done only by a doctor skilled in the clinical procedures described above. Id. “Moreover, the [clinical physician’s] capacity to make judgments in cases of a kind which he has never seen before must depend ultimately on a cultivated capacity to see equivalences between quite disparate things, that is, on analogy.” Murphy, at 9. In sum, hard or Newtonian scientific knowledge does not comprehend all subjects that theoretically might be subjected to its methodology. It is knowledge of a particular and limited kind, gathered or tested by a particular and characteristic method. T.H. Savory, The Language of Science (1953). Although clinical medicine utilizes parts of some hard sciences, clinical medicine and many of its subsidiary fields are not hard sciences. The purposes, criteria, values and methods of hard or Newtonian science and clinical medicine are far from identical. Fred A. Mettler, The Medical Sourcebook xxxiv (1959). Consequently, the Daubert factors, which are hard scientific methods selected from the body of hard scientific knowledge and methodology generally are not appropriate for use in assessing the relevance and reliability of clinical medical testimony. Instead, the trial court as gatekeeper should determine whether the doctor’s proposed testimony as a clinical physician is soundly grounded in the principles and methodology of his field of clinical medicine. B. Rule 703 Rule 703 provides that: The facts or data in the particular ease upon which an expert bases an opinion or inference may be those perceived by or made known to the expert at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence. Prior to Daubert, this court took the position that, before admitting expert testimony, a trial court, as part of or in addition to its preliminary inquiry under Rule 703, must apply the Frye test, i.e., the court must determine that the witness used a well-founded methodology or mode of reasoning sufficiently established to have gained general acceptance in the particular field in which it belongs. Christophersen v. Allied-Signal Corp., 939 F.2d 1106, 1110, 1111, 1115 (5th Cir.1991). In Daubert, however, the Supreme Court held that the Frye “general acceptance” test was displaced by the adoption of the Federal Rules of Evidence. Daubert, 509 U.S. at 588-589, 113 S.Ct. at 2793-2794. The court stated that the “general acceptance” test is at odds with the “liberal thrust” of the Federal Rules of Evidence and their “general approach of relaxing the traditional barriers to ‘opinion’ testimony,” and concluded that Frye is “incompatible with the Federal Rules of Evidence [and] should not be applied in federal trials.” Id. Therefore, any requirement that the trial court apply the Frye “general acceptance” test in determining the admissibility of expert testimony under the Federal Rules of Evidence is no longer tenable in light of the Supreme Court’s decision in Daubert that the test should not be applied in federal trials. Accordingly, we now read the Federal Rules of Evidence, including Rule 703, without the influence of a Frye-focal lens. Under rale 703, a qualified expert may apply his relevant and reliably grounded knowledge and expertise to facts and data in the particular case in order to form and express a pertinent opinion or inference. The facts or data may be derived from (1) the first hand observation of facts, data, or opinions perceived by the witness before trial, (2) the facts, data or opinions presented at trial (as by the familiar hypothetical question or by having the expert attend the trial and hear the testimony establishing the facts, data, and opinions relied on), or (3) facts, data or opinions presented to the expert outside of court other than by his own direct perception. Fed.R.Evid. 703 advisory committee’s note. If they are of a type reasonably relied upon by experts in the field, such facts, data or opinions presented to the expert out of court need not be admitted or even admissible in evidence. United States v. Harper, 802 F.2d 115, 121 (5th Cir.1986). The rale is designed to bring the judicial practice into line with the practice of experts themselves when not in court. United States v. Williams, 447 F.2d 1285, 1290 (5th Cir.1971), cert. denied, 405 U.S. 954, 92 S.Ct. 1168, 31 L.Ed.2d 231 (1972), reh’g denied, 405 U.S. 1048, 92 S.Ct. 1308, 31 L.Ed.2d 591 (1972). The Advisory Committee Note accompanying Rule 703, in part, states: Thus a physician in his own practice bases his diagnosis on information from numerous sources and of considerable variety, including statements by patients and relatives, reports and opinions from nurses, technicians and other doctors, hospital records, and X rays. Most of them are admissible in evidence, but only with the expenditure of substantial time in producing and examining various authenticating witnesses. 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. See also United States v. Burrell, 505 F.2d 904 (5th Cir.1974); United States v. Williams, 447 2d. at 1290. The question of whether facts, data or opinions not admitted in evidence are of a type reasonably relied upon is a preliminary one for the court. Bauman v. Centex Corp., 611 F.2d 1115 (5th Cir.1980); United States v. Lawson, 653 F.2d 299 (7th Cir.1981), cert. denied, 454 U.S. 1150, 102 S.Ct. 1017, 71 L.Ed.2d 305 (1982); Michael H. Graham, Handbook of Federal Evidence § 703.1 (4th Ed.1996). Although only the terms “facts or data” appear in Rule 703, an opinion not in evidence, even if not admissible, may also form the basis of an expert’s opinion if reasonably relied upon by experts in the particular field. See Graham, at p. 109-110, n. 18 (citing the Advisory Committee Note to Rule 703). In determining the preliminary question of whether reliance by the expert is reasonable, the party calling the witness must satisfy the court, both that such facts, data or opinions are of the type customarily relied upon by experts in the field and that such reliance is reasonable. See Christophersen v. Allied-Signal, Corp., 939 F.2d 1106, 1113-1114 (5th Cir.1991) (en banc); Bryan v. John Bean Div. of FMC Corp. 566 F.2d 541, 544-47 (5th Cir.1978). But see Peteet v. Dow Chemical Co. 868 F.2d 1428, 1432 (5th Cir.1989), cert. denied, 493 U.S. 935, 110 S.Ct. 328, 107 L.Ed.2d 318 (1989) (in making the 703 determination, “the trial court should defer to the expert’s opinion of what data they find reasonably reliable.”); See also, 3 Weinstein’s Evidence ¶ 703[03] at 703-17(1981). Daubert’s description of the trial judge’s duty as gatekeeper under Rule 702 sheds light on her duty in this capacity under Rule 703 and the relationship between these duties. The trial judge’s duty under Rule 702 is to determine whether the expert is qualified; whether his proffered opinion is grounded in the methodology of his discipline, i.e., the body of principles, methods, rules and postulates of his field of expertise; and whether his opinion is relevant to the case. In Daubert, the Supreme Court stated that a judge assessing a proffer must also pay attention to Rule 703, which “provides that expert opinions based on otherwise inadmissible hearsay are to be admitted only if the facts or data are. ‘of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject.’” Daubert, 509 U.S. at 595, 113 S.Ct. at 2797. Accordingly, the trial judge as gatekeeper has a duty under Rule 703 to determine whether such facts and data not admitted in evidence are of the type customarily relied upon by experts in the field and whether such reliance is reasonable. Therefore, it may be inferred that the duties of a judicial gatekeeper in assessing an expert opinion under Rules 702 and 703 are roughly similar to those of an appellate court in reviewing the combined legal and factual decisions of a trial judge. This is because the expert and the trial judge perform similar functions in applying specialized knowledge to facts to reach a conclusion or decision about an issue in a case. Consequently, the appellate court and the gatekeeper also perform similar functions in reviewing the work of the trial court and the expert to determine whether their conclusions are soundly grounded in the correct principles of knowledge and are based on properly and reasonably found facts and data. C. Rule 403 Rule 403 provides that: Although relevant, evidence may be excluded if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues, or misleading the jury, or by considerations of undue delay, waste of time, or needless presentation of cumulative evidence. The Supreme Court in Daubert admonished that a judge performing her gatekeeping duties under Rule 702 should also be mindful of other applicable rules, including Rule 403. Daubert, 509 U.S. at 595, 113 S.Ct. at 2797. The court stated that “Rule 403 permits the exclusion of relevant evidence ‘if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues, or misleading the jury...Id. The court quoted Judge Weinstein as explaining: “ ‘Expert evidence can be both powerful and quite misleading because of the difficulty in evaluating it. Because of this risk, the judge in weighing possible prejudice against probative force under Rule 403 of the present rules exercises more control over experts than over lay witnesses.’ Weinstein, 138 F.R.D., at 632.” 509 U.S. at 595, 113 S.Ct. at 2797. As Rule 403 favors the admissibility of relevant evidence, such evidence is to be excluded only if its probative value is substantially outweighed by the danger of unfair prejudice. United States v. Davis, 639 F.2d 239, 244 (5th Cir.1981); See 22 Wright & Graham, Federal Practice and Procedure: Evidence § 5221. Moreover, Rule 403 is an extraordinary remedy to be used sparingly because it permits the trial court to exclude otherwise relevant evidence. E.g., United States v. Thevis, 665 F.2d 616, 633, (5th Cir. Unit B), cert. denied, 456 U.S. 1008, 102 S.Ct. 2300, 73 L.Ed.2d 1303 (1982). There must be a danger of unfair prejudice, not merely the danger of prejudice inherent in any relevant evidence; and its probative value must be substantially outweighed by that danger. As this court stated in United States v. McRae, 593 F.2d 700, 707 (5th Cir.), cert denied, 444 U.S. 862, 100 S.Ct. 128, 62 L.Ed.2d 83 (1979): Relevant evidence is inherently prejudicial; but it is only unfair prejudice, substantially outweighing probative values, which permits exclusion of relevant matter under Rule 403. Unless trials are to be conducted on scenarios, on unreal factors tailored and sanitized for the occasion, the application of Rule 403 must be cautious and sparing. Its major function is limited to excluding matter of scant or cumulative probative force, dragged in by the heels for the sake of its prejudicial effect. As to such, Rule 403 is meant to relax the iron rule of relevance, to permit the trial judge to preserve the fairness of the proceedings by exclusion despite its relevance. It is not designed to permit the court to“ ‘even out’ the weight of the evidence, to mitigate a crime, or to make a contest where there is little or none.”(emphasis in original) “Virtually all evidence is prejudicial or it isn’t material. The prejudice must be ‘unfair.’ ” Dollar v. Long Mfg. N.C., Inc., 561 F.2d 613, 618 (5th Cir.1977), cert. denied, 435 U.S. 996, 98 S.Ct. 1648, 56 L.Ed.2d 85 (1978). The Advisory Committee Note on Rule 403 provides that “[u]nfair prejudice within this context means an undue tendency to suggest decision on an improper basis, commonly, though not necessarily, an emotional one.” For example, evidence may be unfairly prejudicial because it appeals to the jury’s sympathies, arouses its sense of horror, provokes its instinct to punish, triggers other mainsprings of human action, or may cause a jury to base its decision on something other than the established propositions of the case. 3 Weinstein & Berger ¶403[03] 403-37 to 403-40 (citing authorities including United States v. Bowers, 660 F.2d 527 (5th Cir.1981); United States v. Osum, 943 F.2d 1394, 1404 (5th Cir.1991); United States v. Kang, 934 F.2d 621, 628 (5th Cir.1991)). In addition, evidence may threaten “confusion of the issues, or misleading the jury” when “the probability that the proof and the answering evidence that it provokes may create a side issue that will unduly distract the jury from the main issues.” McCormick, McCormick On Evidence § 185(West 2d ed.1972); See Ford v. Sharp, 758 F.2d 1018 (5th Cir.1985). III. Background Facts On April 23, 1990, Bob T. Moore, a delivery truck driver for Consolidated Freight-ways, Inc., a motor freight company, delivered a shipment of solvents containing mixed chemicals to Ashland Chemical, Inc. Bart Graves, Ashland’s plant manager was on the loading dock when Moore arrived. When the back door of the trailer opened, chemical gases were escaping from two leaking drums. Graves notified Dow Corning Corporation, the manufacturer and shipper of the chemical solvents, of the spill and requested clean up instructions. At Graves’ request, Dow Corning faxed him a copy of the Material Safety Data Sheet (“MSDS”) regarding the spilled chemical solvents. The MSDS notified Graves of the nature of the chemical contents in the solvents and the health problems associated with exposure to the chemical mixture’s vapors. Significantly, the MSDS stated that the solvents contained a blend of chemicals, including toluene, naphtha, and propylene glycol methyl ether. It warned that inhalation of their vapors could result in injury to the blood, liver, lungs, kidneys, and nervous system. To prevent such injuries, the MSDS cautioned that, in the event of a spill, respiratory protection equipment should be worn unless there is adequate ventilation, or the level of contaminants was below a specified level. Moore was not shown or informed of the contents of the MSDS. Moore’s rig consisted of a diesel tractor and a 28 foot enclosed trailer. Ventilation in the trailer was limited. Moore told Graves that he wanted to return to Consolidated Freightways and have other employees clean it out. Graves told Moore, however, that the bill of lading would not be signed until after the spill in the trailer was cleaned up. Moore telephoned his supervisor who told Moore to comply with Ashland’s demands regarding the spill clean up. Graves directed Moore to clean up the trailer by placing absorbent material on the chemicals, sweeping them up, and disposing of them in “over-packs” to be placed in the leaking drums. During the clean up, Moore informed Graves of his recent recovery from pneumonia and requested the use of a respirator to which Graves had access. Graves refused, despite his knowledge of the lack of ventilation in the trailer. Graves also failed to measure the amount of contaminants in the trailer, although he had access to a meter provided by Ashland for this purpose. The clean up job took between 45 minutes and an hour. Within an hour or so after cleaning up the spill, Moore began to suffer dizziness, watery eyes, and difficulty in breathing. When he returned to Consolidated Freightways, Moore informed his supervisor that he was sick and he was sent to the company doctor. The next day, Moore saw his family physician, who treated him for two to three weeks. Moore then placed himself under the care of Dr. Simi, a pulmonary specialist. Dr. Simi prescribed' medication for Moore and released him to work. Moore returned to work during June 1990, but terminated his employment a few weeks later because of his respiratory difficulties. On June 26, 1990 and subsequently, Moore was seen by Dr. Daniel Jenkins, a pulmonary, environmental and internal medicine specialist. After seeing Moore three times in June, July and August 1990, Dr. Jenkins diagnosed Moore’s condition as reactive airways dysfunction syndrome (“RADS”). On November 29, 1990, Moore was seen by Dr. Antonio Alvarez, a pulmonary and internal medicine specialist, who became his treating physician. Dr. Alvarez confirmed and adopted Dr. Jenkins’ diagnosis and treated Moore for his disease up to and during the trial. By this time, Moore’s condition had deteriorated, he was still unable to work, and he was forced to carry a container of oxygen at all times. IV. Moore’s Proffers of Expert Clinical Medical Testimony The plaintiffs set out to prove that Moore’s personal injury, viz., his reactive airways disease, was proximately caused by his exposure to the mixture of chemicals he encountered at Ashland’s premises. Moore’s case depended on expert testimony that his disease was reactive airways disease and that it had been caused by his exposure to the chemicals at Ashland. The plaintiffs proffered the opinions and inferences of Dr. Daniel E. Jenkins and Dr. B. Antonio Alvarez based on their clinical medical knowledge and facts and data in this particular ease for these purposes. A. Dr. Jenkins Dr. Jenkins received his medical degree from the University of Texas in 1940. He received medical training at the University of Michigan Hospital as an intern, resident in medicine, resident in Tuberculosis and Chest Disease, and resident in Allergy in 1940-1945. The American Board of Internal Medicine certified him in 1947. Between 1943 and 1947 he served as Instructor and Chief Resident in Medicine and as Assistant Professor of Medicine and Physician in charge of the Tuberculosis and Chest Unit, University of Michigan Medical School. From 1947 to 1991 he served as Assistant Professor, Associate Professor, and Professor of Medicine at Baylor College of Medicine, Houston, Texas. From 1947 to 1974 he was Chief, Pulmonary Disease Section, Baylor College of Medicine. From 1975 to 1991 he was Chief, Environmental Medicine, Baylor College of Medicine. In 1991, he went into practice with The Respiratory Consultants of Houston, consisting mostly of a group of physicians that he had trained. He is either Attending Physician or Consultant in Medicine or Pulmonary Medicine at eight Hospitals in Houston, Texas. Additionally, Dr. Jenkins is a member of sixteen national, state and local medical organizations and has served as president or chairman of a section for three of them. In formulating his opinion, Dr. Jenkins personally took a detailed medical history from Moore, performed a thorough physical examination, personally observed him three times, performed or supervised a series of tests on Moore including pulmonary function tests, a bronchial challenge test, a bronchodilator test, a spirometry test, a plethysmographic test, a lung volume determination, an intrapul gas distribution test, a diffusion test, an arterial bloods test, a mechanics test, X-rays, and laboratory tests, reviewed the medical records and reports of Dr. Alvarez and Dr. Simi, including a report of the bronchial dilator test by Dr. Simi two or three weeks after the accident that showed severe airways obstruction and a report of an allergy test performed by Dr. Alvarez — among some fifteen reports of examinations and tests by him — that ruled out allergic or immunologic disease and confirmed reactive airways disease as the proper diagnosis of Moore’s illness, reviewed the material safety data sheet “MSDS” prepared by Dow Corning, and consulted a medical treatise, Carl Zenz, Occupational Medicine: Principles and Practical Application (2d ed.1988) and other medical literature. In his proffered testimony, Dr. Jenkins explained that reactive airways disease, also known as reactive airways dysfunction syndrome (RADS), is recognized in the field of clinical medical knowledge as a disorder consisting of a reactive obstruction of air passageways in the bronchial trees and the lower respiratory tract, producing labored breathing, wheezing, shortness of breath, coughing and the raising of phlegm. Dr. Jenkins’ testimony as to the nature and symptoms of reactive airways disease was accepted as accurate by the parties and other experts on both sides: In the history taken by Dr. Jenkins, Moore reported that he had been in comparatively good health until about one hour after his exposure to the chemical gases at Ashland when he began to experience these types of symptoms. In his physical examinations and tests of Moore, Dr. Jenkins observed symptoms and signs of reactive airways disease. Dr. Jenkins stated that the objective medical tests performed by him and the several doctors who had seen Moore after his exposure indicated conclusively that Moore was not malingering. Dr. Jenkins offered his opinion that Moore suffered from reactive airways disease that had been caused by Moore’s exposure to gases emanating from a spill of blended chemicals which Moore had cleaned up without a respirator. He testified that the manufacturer’s material safety data sheet stated that the principal substances contained in the mixture of chemicals that Moore breathed were toluene, naphtha, and propylene glycol methyl ether, and that all of these have irritating properties. He further stated that any chemical with irritating properties can cause reactive airways disease in a person who is capable of responding in that way. Dr. Jenkins also stated that toluene, one of the chemicals to which Moore was exposed, is similar to the chemical nature of other properties upon which there have been written articles on reactive airways disease. Dr. Jenkins testified that, based on the history given by Moore that a substantial amount of the mixed chemical solvent had leaked onto the truck-trailer floor from two 55 gallon drums while the cargo was enclosed and en route, he roughly estimated that Moore had been exposed to 200 parts per million or higher of the chemical vapors. Dr. Jenkins also testified that Moore informed him that neither Ashland nor anyone else had taken air samples with mechanical devices at the time of Moore’s exposure. Although Dr. Jenkins acknowledged that he could not recall having seen a patient who had been exposed to the same chemicals under the same circumstances, he testified that he had examined and evaluated over one hundred other patients who had been exposed to chemicals under various circumstances. During Dr. Jenkins’ deposition, the interrogating lawyers and the doctor sometimes referred to the mixed chemical spillage as “toluene,” which was in fact just one of its many ingredients. But a fair reading of the deposition as a whole clearly indicates that when the lawyers and Dr. Jenkins used the word “toluene” they intended to refer to the chemical mixture containing toluene and simply called the solvent mixture “toluene” for the sake of convenience. Dr. Jenkins’ proffered testimony was that, based on his education, knowledge, training, and experience, personal examination of Moore, personal taking of Moore’s history, supervision and study of his own tests on Moore, review and study of other doctors’ reports, tests and opinions, study of a medical treatise and numerous medical literature articles, he concluded that Moore’s exposure to the mixture of chemical gases contained in the solvent to which he was exposed caused his disease, because any chemical with irritating properties can cause reactive airways disease, and each of the chemicals in the solvent mixture had irritating properties. B. Dr. Alvarez Dr. Alvarez testified that he was born in Mexico and came to the United States in 1964 for internship and residency in internal medicine, followed by two years of fellowship in pulmonary at the Baylor College of Medicine in Houston. Dr. Daniel E. Jenkins was one of Dr. Alvarez’s professors at the Baylor College of Medicine. Dr. Alvarez had practiced in Houston since 1973 and was on the active staff of three, and courtesy staff of one, Houston area hospitals. At the proffer stage, Dr. Alvarez, offered his opinion based on clinical medical knowledge as an internist and pulmonary specialist, enhanced by his experience in having seen fifty to sixty patients injured from exposure to chemicals, and on the facts and data contained in the medical history taken by Dr. Jenkins, the X-rays and numerous medical tests performed by Dr. Jenkins, a sinus X-ray, an allergy or RAST test performed by Dr. Alvarez tending to rule out allergies as the cause of the illness, numerous physical examinations and observations of Moore, and the manufacturer’s material data sheet pertaining to the chemicals to which Moore was exposed. Applying his knowledge, education, training and experience to these facts and data, but admittedly relying heavily on Dr. Jenkins’ work and opinion, Dr. Alvarez expressed his opinion that Moore suffered from reactive airways disease that had been caused by his inhalation of chemical gases while he was cleaning up the chemical spillage at Ashland. When asked whether he relied heavily on the evaluation and documentation provided from Dr. Jenkins, Dr. Alvarez replied “very much.” In addition, he testified that he had not seen the history and evaluations of Dr. Warren Simi first hand. Dr. Alvarez was asked how important it was to know the duration of an exposure, the amount of chemical present, the dimensions of the area or enclosure, the ventilation, and the temperature: In response, Dr. Alvarez indicated that if such data were available it would be very important, but, he explained, it is always very difficult for a medical doctor, who must make decisions as to causation and diagnosis in treating patients accidentally exposed to chemicals or other toxic substances, to obtain exact or mechanically measured data on these issues because of the very fact that the injury always results from an accident and not a controlled experiment. C. Dr. Jenkins’ opinion as to causation was soundly grounded in traditional clinical medical knowledge, principles and methodology. Dr. Jenkins, a specialist in pulmonary and environmental disease, based his opinion on principles, theories, methodology and techniques, which are well accepted within his discipline. In summary, the proffered testimony of Dr. Jenkins reflects that he: 1) Examined Moore personally: Dr. Jenkins saw Moore on three occasions, between June 26, and August 1, 1990. On each occasion the doctor personally observed the patient. The doctor performed a thorough physical examination of Moore. (Personal observation has always been an adequate basis for an expert’s opinion, and indeed has been called “ ‘the most desirable of all bases.’ ” 3 Weinstein ¶ 703[01], 703-7; Rheingold, The Basis of Medical Testimony, 15 Vand.L.Rev. 473, 489 (1962)). ■ 2) Personally took a detailed medical history from Moore: Dr. Jenkins personally took Moore’s history involving his health and the accident in an interview of approximately one and one-half hours. (“Reliance on patient statements to render a medical opinion is usually justified as trustworthy because patients have a strong incentive to tell their treating physician the truth — the desire to recover.” In re Agent Orange Product Liability Litigation, 611 F.Supp. 1223, 1246 (E.D.N.Y.1985); Rheingold, supra at 495; Ferebee v. Chevron Chemical Co., 736 F.2d 1529, 1535 (D.C.Cir.1984)(especially when corroborated by medical records, physical examination, and medical tests); See O’Gee v. Dobbs Houses, Inc., 570 F.2d 1084 (2d Cir.1978); Birdsell v. United States, 346 F.2d 775, 780 (5th Cir.1965); Rheingold, supra at 488.) 3) Used Differential Diagnosis and Etiology: In his determination of the cause and nature of the disease, Dr. Jenkins performed or supervised a series of tests on Moore. He studied, compared and synthesized the results so as to eliminate all possibilities but the most likely diagnosis and cause of the disorder. The gamut of tests performed on Moore included pulmonary function tests, a bronchial challenge test, a bronchodilator test, an allergy test, X-rays, and laboratory tests. Dr. Jenkins and Dr. Alvarez testified that it would have been impossible for Moore to fake RAD signs on the objective tests. See Birdsell v. United States, 346 F.2d 775, 779-780 (5th Cir.1965) (“[T]he physician making a diagnosis must necessarily rely on many observations and tests performed by others and recorded by them; records sufficient for diagnosis in the hospital ought to be enough for opinio