San Francisco v. Wendy's International, Inc.

In this appeal from the Circuit Court of Kanawha County, we are asked to examine an order precluding the plaintiffs below from presenting the testimony of two expert witnesses in a case of food poisoning. The circuit court then went on to grant summary judgment to the defendant, on the basis that the plaintiffs did not have sufficient evidence to support their claim. On appeal, the parties debate whether the two experts — a treating physician and a director of a university food safety program — were qualified to testify and whether their opinions were sufficiently reliable to be admissible under Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993) and Wilt v. Buracker, 191 W.Va. 39, 443 S.E.2d 196 (1993).

After careful review of the record, and of the excellent briefs and arguments by the parties, we find that the circuit court erred in excluding the two experts. As set forth below, we reverse the circuit court’s summary *739judgment order, and remand the case for further proceedings.

I.

Facts & Background

Around noon on May 1, 2002, appellants Clinton and Jessie San Francisco visited a restaurant in Charleston, West Virginia, owned by the appellee, Wendy’s International, Inc. (“Wendy’s”). At the restaurant’s drive-through window, Mr. San Francisco purchased, among other items, a “single”sized hamburger with mustard, onions, pickles and tomato. The appellants then drove off and began eating their meals in the car.

Mr. San Francisco had eaten approximately one-quarter of his hamburger when he noticed that the burger was “red inside and wasn’t done, it was raw,” “tasted funny” and that the texture was “soft.” After this observation, Mr. San Francisco discarded the remainder of the hamburger.

Shortly thereafter, Mr. San Francisco became ill. His stomach began to bother him and he began to sweat profusely. Within one-and-a-half to two hours after eating the hamburger, Mr. San Francisco began experiencing vomiting and diarrhea.

Two days later, after continued pain and discomfort, on May S, 2002, Mr. San Francisco was admitted to Logan General Hospital.1 He remained in the hospital until May 13, 2002.

While at Logan General, Mr. San Francisco was treated by Dr. Peter Gregor, a physician who is board certified in internal medicine and cardiology and is familiar, based on his clinical experience, with a food poisoning diagnosis. Dr. Gregor conducted a work up and analysis of Mr. San Francisco and performed a “differential diagnosis” to determine the cause of his illness. Using this method of diagnosis, during his examination, Dr. Gregor considered and then ruled out other potential causes of Mr. San Francisco’s illness, such as pre-existing gastrointestinal problems, alcohol use, peptic ulcer disease or diverticulitis. After considering Mr. San Francisco’s history and condition — particularly noting that he vomited 1.8 liters of material while in the emergency room, an amount which Dr. Gregor considered substantial — Dr. Gregor concluded to a reasonable degree of medical certainty that Mr. San Francisco was suffering from a foodborne illness caused by the Wendy’s hamburger. As Dr. Gregor later stated in his deposition:

If you ask me, do I think a hamburger at a restaurant with diarrhea, vomiting and fluid loss shortly thereafter was the cause of the hospitalization, I would say yes_It was the hamburger.

On April 19, 2004, Mr. and Mrs. San Francisco filed the instant lawsuit against appellee Wendy’s, alleging that the appellee had caused injury to Mr. San Francisco by selling an “unsafe, unwholesome, or unfit food product.”

During discovery, the appellants identified two experts. The appellants identified Dr. Gregor as an expert who would testify that Mr. San Francisco suffered from a foodborne illness caused by the Wendy’s hamburger. The appellants also identified Ewen Todd, Ph.D., an expert in food safety and toxicology from Michigan State University. Dr. Todd testified in a deposition that although the symptoms of Mr. San Francisco’s illness were most consistent with verotoxin produced by E. coli 0157:H7 bacteria, he became ill too quickly for a typical E. coli infection to have occurred; E. coli bacteria apparently require incubation of three to seven days from ingestion to produce enough verotoxin to induce symptoms. Instead, Dr. Todd was of the opinion that E. coli bacteria was present on the ground beef in the Wendy’s hamburger; that the bacteria had produced vero-toxin; and that the ingestion of the verotoxin in the Wendy’s hamburger had produced the rapid onset of Mr. San Francisco’s symptoms. Dr. Todd’s opinion was based upon a published scientific study which found that four days after E. coli bacteria was added to ground beef, verotoxins formed in the beef.2

*740After the completion of discovery, appellee Wendy’s filed a motion for summary judgment — and subsequently, motions in limine — to exclude the testimony of Dr. Gre-gor and Dr. Todd. The appellee argued that Dr. Gregor was unqualified to render medical testimony on injury and causation, and that neither Dr. Gregor’s opinion nor Dr. Todd’s opinion met the standards of admissibility under Rule 702 of the West Virginia Rules of Evidence, Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993) and Wilt v. Buracker, 191 W.Va. 39, 443 S.E.2d 196 (1993).

In an order dated March 14, 2006, the circuit court excluded the testimony of Dr. Gregor and Dr. Todd, and granted summary judgment to the appellee. The circuit court concluded that under Rule 702, Dr. Gregor was not “qualified as an expert by knowledge, skill, experience, training or education.” Further, the circuit court found that Dr. Todd’s opinion was “unreliable as a matter of law and inadmissible” under Daubert and Wilt. In the absence of the testimony of the two experts, the circuit court found insufficient evidence that Mr. San Francisco suffered from a foodborne illness caused by the Wendy’s hamburger, and therefore granted summary judgment to the appellee.

The appellants now appeal the circuit court’s March 14, 2006 order.

II.

Stand,ard, of Review

Our review of a circuit court’s decision to grant a party a summary judgment under Rule 56 of the Rules of Civil Procedure is reviewed de novo. Syllabus Point 1, Painter v. Peavy, 192 W.Va. 189, 451 S.E.2d 755 (1994). Similarly, when we review a circuit court’s decision that turns upon an interpretation of the West Virginia Rules of Evidence, a question of law is presented that is subject to a de novo review. Syllabus Point 1, Gentry v. Mangum, 195 W.Va. 512, 466 S.E.2d 171 (1995).

When considering the propriety of a circuit court’s decision to admit or exclude the testimony of an expert witness, we generally examine the decision for an abuse of discretion. As we stated in Syllabus Point 6 of Helmick v. Potomac Edison Co., 185 W.Va. 269, 406 S.E.2d 700 (1991):

The admissibility of testimony by an expert witness is a matter within the sound discretion of the trial court, and the trial court’s decision will not be reversed unless it is clearly wrong.

See also Syllabus Point 5, Overton v. Fields, 145 W.Va. 797, 117 S.E.2d 598 (1960) (‘Whether a witness is qualified to state an opinion is a matter which rests within the discretion of the trial court and its ruling on that point will not ordinarily be disturbed unless it clearly appears that its discretion has been abused.”)

However, when a circuit court excludes expert testimony as unreliable under the Daubert/Wilt gatekeeper analysis, we will review the circuit court’s method of conducting the analysis de novo. Syllabus Point 3, in part, Gentry v. Mangum, supra. (“Under Daubert ... and Wilt ... the reliability requirement is met only by a finding by the trial court under Rule 104(a) of the West Virginia Rules of Evidence that the scientific or technical theory which is the basis for the test results is indeed ‘scientific, technical, or specialized knowledge.’ The trial court’s determination regarding whether the scientific evidence is properly the subject of scientific, technical, or other specialized knowledge is a question of law that we review de novo ”). See also Norris v. Baxter Healthcare Corp., 397 F.3d 878, 883 (10th Cir.2005) (“We review de novo whether the district court applied the proper standard in determining whether to admit or exclude expert testimony.”).

With these standards in mind, we turn to the parties’ arguments.

III.

Discussion

A.

General Principles under Rule 702

The appellants argue that the circuit court misinterpreted the West Virginia Rules of *741Evidence regarding the admission of expert testimony, resulting in the improper exclusion of the opinions of Dr. Gregor and Dr. Todd about Mr. San Francisco’s injury and its cause. While the admissibility of expert testimony is governed by Rule 702 of the Rules of Evidence, several significant cases interpreting that rule — -namely Wilt v. Buracker, 191 W.Va. 39, 443 S.E.2d 196 (1993) and Gentry v. Mangum, 195 W.Va. 512, 466 S.E.2d 171 (1995) — impose a “gatekeeper” duty upon trial courts to screen scientific expert opinions to ensure they are both relevant to the case and based upon reliable methodologies. Accordingly, the issue in this case is whether the circuit court properly performed its “gatekeeper” function under Rule 702.

“The Rules of Evidence embody a strong and undeniable preference for admitting any evidence which has the potential for assisting the trier of fact.” Kannankeril v. Terminix International, Inc., 128 F.3d 802, 806 (3rd Cir.1997). To assist the trier of fact, Rule 702 of the Rules of Evidence permits opinion testimony by an expert, and states:

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.

“Rule 702 reflects an attempt to liberalize the rules governing the admissibility of expert testimony.” Weisgram v. Marley Co., 169 F.3d 514, 523 (8th Cir.1999). See also Gentry v. Mangum, 195 W.Va. at 520, 466 S.E.2d at 179. (“In Daubert/Wilt, the Frye test was abandoned by the courts, concluding that Frye’s rigid standard was inconsistent with the liberal thrust of the Federal and West Virginia Rules of Evidence.”); Beech Aircraft Corp. v. Rainey, 488 U.S. 153, 169, 109 S.Ct. 439, 102 L.Ed.2d 445 (1988) (highlighting the “ ‘liberal thrust’ of the Federal Rules and their ‘general approach of relaxing the traditional barriers to opinion testimony.’ ”). The rule “is one of admissibility rather than exclusion.” Arcaren v. United States, 929 F.2d 1235, 1239 (8th Cir.1991).

Following in the footsteps of the U.S. 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), we determined in Wilt that trial courts have a gatekeeping function under Rule 702 for determining the admissibility of expert scientific testimony. In Wilt, and later in Gentry, we explained that circuit courts must conduct a two-part inquiry under Rule 702 and ask: (1) is the witness an expert; and, if so, (2) is the expert’s testimony relevant and reliable?

As to the first part of the inquiry, in Syllabus Point 5 of Gentry the Court explained the steps that a trial court should take to determine if an expert is qualified to render an opinion under Rule 702:

In determining who is an expert, a circuit court should conduct a two-step inquiry. First, a circuit court must determine whether the proposed expert (a) meets the minimal educational or experiential qualifications (b) in a field that is relevant to the subject under investigation (c) which will assist the trier of fact. Second, a circuit court must determine that the expert’s area of expertise covers the particular opinion as to which the expert seeks to testify.

“Rule 702 permits a circuit court to qualify an expert by virtue of education or experience or by some combination of these attributes .... [W]e have stated clearly that a broad range of knowledge, skills, and training qualify an expert as such, and rejected any notion of imposing overly rigorous requirements of expertise.” Gentry, 195 W.Va. at 524-25, 466 S.E.2d at 183-84.

Second, if the expert is qualified, the analysis turns to whether the expert’s proffered opinion is relevant and reliable. In Wilt, this Court adopted a standard similar to that established by the United States Supreme Court in Daubert. The Wilt Court stated, in Syllabus Point 2, that:

In analyzing the admissibility of expert testimony under Rule 702 of the West Virginia Rules of Evidence, the trial court’s initial inquiry must consider whether the testimony is based on an assertion or inference derived from the scientific *742methodology. Moreover, the testimony must be relevant to a fact at issue. Further assessment should then be made in regard to the expert testimony’s reliability by considering its underlying scientific methodology and reasoning. This includes an assessment of (a) whether the scientific theory and its conclusion can be and have been tested; (b) whether the scientific theory has been subjected to peer review and publication; (c) whether the scientific theory’s actual or potential rate of error is known; and (d) whether the scientific theory is generally accepted within the scientific community.

We later expounded upon our holding in Wilt in Syllabus Point 4 of Gentry, where we explained:

When scientific evidence is proffered, a circuit court in its “gatekeeper” role under Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993), and Wilt v. Buracker, 191 W.Va. 39, 443 S.E.2d 196 (1993), cert denied, 511 U.S. 1129, 114 S.Ct. 2137, 128 L.Ed.2d 867 (1994), must engage in a two-part analysis in regard to the expert testimony. First, the circuit court must determine whether the expert testimony reflects scientific knowledge, whether the findings are derived by scientific method, and whether the work product amounts to good science. Second, the circuit court must ensure that the scientific testimony is relevant to the task at hand.

As noted above, Daubert and Wilt provide several factors a trial court can apply to assess the reliability of expert testimony: whether the scientific theoiy and its conclusion can be or have been tested; whether the scientific theoiy has been subjected to peer review and publication; whether the scientific theory’s actual or potential rate of error is known; and whether the scientific theory is generally accepted within the scientific community. Syllabus Point 2, Wilt.

These factors are by no means a definitive checklist or test of reliability. Other courts have developed additional factors, such as whether the scientific theory “was developed for litigation or naturally flowed from the expert’s research; whether the proposed expert ruled out other alternative explanations; and whether the proposed expert sufficiently connected the proposed testimony with the facts of the case.” Lauzon v. Senco Products, Inc., 270 F.3d 681, 687 (8th Cir.2001) (citations omitted). Sometimes, a theory first appears in court because of “(a) the inability to publish in a peer review journal because of industry control, (b) the testimony is not novel and therefore of little publication interest, [or] (c) the topic is of little general interest.” Larry E. Coben, Crashworthiness Litigation, § 24:4 [1998]. A court may treat an expert’s qualifications as circumstantial evidence that he or she has used a scientifically valid methodology or mode of reasoning in drawing his or her conclusions. Ambrosini v. Labarraque, 101 F.3d 129, 140 (D.C.Cir.1996). In sum, regardless of what other factors a court considers, an expert’s opinion is still reliable and admissible if “the expert explains precisely how the conclusions were reached and points to an objective source to show that his or her conclusions are based on a scientific method used by at least a minority of scientists in the field.” Coben, Crashworthiness Litigation,3

When assessing the reliability of an expert’s opinion, a trial court’s role as a “gatekeeper” is to determine whether the reasoning or methodology underlying the testimony is scientifically valid. “Evaluating the reliability of scientific methodologies and data does not generally involve assessing the truthfulness of the expert witnesses!.]” Gentry, 195 W.Va. at 519, 466 S.E.2d at 178, quoting in part, In re Paoli R.R. Yard PCB *743Litigation, 35 F.3d 717, 749 (3rd Cir.1994). Instead, under DaubeH/Wilt and Gentry a trial court

conducts an inquiry into the validity of the underlying science, looldng at the soundness of the principles or theories and the reliability of the process or method as applied to the ease. The problem is not to decide whether the proffered evidence is right, but whether the science is valid enough to be reliable.

Gentry, 195 W.Va. at 523, 466 S.E.2d at 182. Put simply, a trial court acting as a gatekeeper should take care to not invade the province of the jury, whose job it is to decide issues of credibility and persuasiveness, and to determine the weight that should be given to the expert’s opinion.

The instant case raises a problem, one that was alluded to by the Court in Gentry, and that is when and how challenges to the reliability of an expert’s testimony are brought under Rule 702 and Daubert/Wilt. Gentry, 195 W.Va. at 522, 466 S.E.2d at 181. Appel-lee Wendy’s sought the exclusion of the testimony of the appellants’ two experts in a motion for summary judgment filed after the close of discovery, but later reiterated its position verbatim in motions in limine filed on the eve of trial. The circuit court heard argument from the parties on both sets of motions in a pretrial hearing, and entered a written order that excluded the testimony of both experts and granted summary judgment to the appellee the same day.

In Gentry, the Court suggested that DaubeH/Wilt challenges to scientific evidence should be rare, and said that “most scientific validity issues will be resolved under judicial notice pursuant to Rule 201.” Id. However, when challenges need to be made, the Gentry Court indicated that motions in limine are likely the best vehicle, because “the best time to review and resolve scientific issues is at the pretrial level.” 195 W.Va. at 521, 466 S.E.2d at 180. In making a motion in limine, the initial burden of production rests on the opponent of the expert’s opinion. 195 W.Va. at 522, 466 S.E.2d at 181.

DaubeH/Wilt challenges can play a role during the summary judgment phase of civil litigation. However, the few courts addressing the issue have concluded that the Dau-bert gatekeeping regime is of limited utility in the context of a summary judgment motion, and have held that the better practice is to permit the parties a hearing to defend the admissibility of an expert’s proffered opinion. As one court stated:

The fact that DaubeH can be used in connection with summary judgment motions does not mean that it should be used profligately. A trial setting normally will provide the best operating environment for the triage which DaubeH demands. Voir dire is an extremely helpful device in evaluating proffered expert testimony ... and this device is not readily available in the course of summary judgment proceedings. Moreover, given the complex factual inquiry required by Daubert, courts will be hard-pressed in all but the most clearcut cases to gauge the reliability of expert proof on a truncated record. Because the summary judgment process does not conform well to the discipline that DaubeH imposes, the DaubeH regime should be employed only with great care and circumspection at the summary judgment stage.

We conclude, therefore, that at the junction where Daubert intersects with summary judgment practice, Daubert is accessible, but courts must be cautious — except when defects are obvious on the face of a proffer — not to exclude debatable scientific evidence without affording the proponent of the evidence adequate opportunity to defend its admissibility.

Cortés-Irizarry v. Corporación Insular de Seguros, 111 F.3d 184, 188 (1st Cir.1997). Like the instant case, in Padillas v. Stork-Gamco, Inc., 186 F.3d 412 (3rd Cir.1999), the appellate court reviewed an order by a'trial court that excluded a plaintiffs expert report under Daubert and then granted summary judgment to a defendant. The Padillas court found the trial court’s failure to hold a hearing to review the DaubeH issue was an abuse of discretion, stating:

We have long stressed the importance of in limine hearings under Rule 104(a) in making the reliability determination required under Rule 702 and DaubeH. See *744United States v. Downing, 753 F.2d 1224, 1241 (3d Cir.1985) (“It would appear that the most efficient procedure that the district court can use in maldng the reliability determination is an in limine hearing.”). In In re Paoli Railroad Yard PCB Litigation, 916 F.2d 829 (3d Cir.1990), we reversed a summary judgment for defendants because the district court, in excluding expert evidence under Rule 703, had failed to “provide [ ] the plaintiffs with sufficient process for defending their evidentiary submissions.” Id. at 854. We explained:

The adversarial process upon which our legal system is based assumes that a fact finder will give the parties an adequate opportunity to be heard; if it does not, it cannot find facts reliably. Thus, the detailed factual record requirement, firmly entrenched in our jurisprudence, requires adequate process at the eviden-tiary stage, particularly when a summary judgment may flow from it.

Id. (citations omitted). We reiterated our Paoli holding in Hines v. Consolidated Rail Corp., 926 F.2d 262, 272 (3d Cir.1991) (“A detailed factual record is required at the evidentiary stage, particularly when a summary judgment may result.”). And in In re Paoli Railroad Yard PCB Litigation, 35 F.3d 717 (3d Cir.1994), we declared:

Given the “liberal thrust” of the federal rules it is particularly important that the side trying to defend the admission of evidence be given an adequate chance to do so.

Id. at 739 (citation omitted); see also Margaret A. Berger, Procedural Paradigms for Applying the Daubert Test, 78 Minn. L.Rev. 1345, 1365 (1994) (reviewing admissibility of expert testimony in light of the “liberal thrust” of the Federal Rules of Evidence).

186 F.3d at 417.

Although courts considering the question have found that in limine hearings are generally recommended prior to maldng a Dwnbert-type determination, they are not required. “The only legal requirement is that the parties ‘have an adequate opportunity to be heard’ before the district court makes its decision.” Group Health Plan, Inc. v. Philip Morris USA, Inc., 344 F.3d 753, 761 n. 3 (8th Cir.2003). But by holding a hearing focused exclusively on the expert’s proffered opinion, both the trial court and this Court on appellate review will be fully informed. As the Mississippi Supreme Court recently stated,

Prior to any Daubeti determination or other decision regarding the proffer of expert evidence, the parties must be afforded the opportunity to be heard. We generally recommend that the trial court conduct an in limine hearing specifically on the subject, as this procedure will result in full briefing and argument by the par-ties regarding the proposed expert testimony. This will not only assist the trial court in its function as evidentiary gatekeeper; it will provide a fuller record for an appellate court should the parties contest the eviden-tiary ruling. While an in limine hearing may not be necessary in all cases, it does provide the most efficient manner of addressing the issue in many cases.

Smith ex rel. Smith v. Clement, — So.2d -, -, 2007 WL 2874937, *3 (Miss. Oct.4, 2007).

We therefore hold that because the summary judgment process does not conform well to the discipline and analysis that Daubert and Wilt impose, the Daubert/Wilt regime should be employed only with great care and circumspection at the summary judgment stage. Courts must be cautious— except when defects are obvious on the face of a proffered expert opinion — not to exclude debatable scientific evidence without affording the proponent of the evidence adequate opportunity to defend its admissibility. Given the plain language of the West Virginia Rules of Evidence, the side trying to defend the admission of expert evidence must be given an adequate chance to do so.

With these guidelines in mind, we turn now to the specific arguments of the parties concerning the proffered expert opinions of Dr. Gregor and Dr. Todd.

*745B.

The Testimony of Dr. Gregor

The appellants argue that the circuit court abused its discretion in excluding Dr. Gregor’s testimony, because (1) Dr. Gregor is qualified as an expert to render an opinion on the identity and cause of appellant Mr. San Francisco’s illness, and (2) Dr. Gregor’s opinion is reliable under Daubert/Wilt.

As to Dr. Gregor’s qualifications as an expert, the appellants assert that Dr. Gregor is a physician board-certified in internal medicine with a sub-specialty in cardiovascular disease. During his time in practice from 1979 until 2002 (some twenty-three years), Dr. Gregor treated numerous gastrointestinal conditions, including diagnosing and treating multiple patients suffering from foodborne illnesses. The appellants point out that the Gentry Court stated that “once an expert passes the minimal threshold, further credentials affect the weight of the testimony not its admissibility." 195 W.Va. at 523 n. 14, 466 S.E.2d at 182 n. 14. The appellants therefore argue that because Dr. Gregor is qualified to diagnose patient illnesses (including foodborne illnesses), diagnose the cause of those illnesses, and then treat patients in a hospital setting, he is similarly qualified to render an opinion on the diagnosis and cause of an illness in a courtroom.

The appellee, however, argues that Dr. Gregor does not have a specialization in gas-troenterology or epidemiology. Further, Dr. Gregor had never testified in court regarding foodborne illnesses prior to this case, had never conducted research or studies on the topic, and had never worked in the fields of epidemiology or public health. The appellee cites to Dr. Gregor’s own deposition testimony, where he admitted that medical experts in other fields would be better qualified to render an opinion:

A. ... And I’m not an expert in the etiology of foodborne illness, nor do I claim to be one today.

Q. Okay. Would you then defer to the opinions of a qualified gastroenterologist or infectious disease expert on those issues regarding etiology?

A. As regards to organism?

Q. Right. Organism or causation.

A. Yes.

The appellee argues that, while Dr. Gregor is highly qualified as a board certified cardiologist, he is not a gastroenterologist, infectious disease physician, public health physician, or epidemiologist — all of which are medical fields that deal specifically with foodborne illnesses. Accordingly, the appellee asserts that the circuit court was fairly persuaded that Dr. Gregor did not possess the necessary threshold of expertise to testify, and properly was within its discretion in excluding Dr. Gregor’s testimony.

After careful consideration, we reject the appellee’s position because it is directly contrary to Rule 702 and our holding in Gentry. Rule 702 states that a broad range of knowledge, skills, and training qualify an expert as such, and Gentry made clear that we have rejected any notion of imposing overly rigorous requirements of expertise. In Gentry, the Court expressed the concern that there is no “best expert” rule, and “[n]either a degree nor a title is essential, and a person with knowledge or' skill borne of practical experience may qualify as an expert.” 195 W.Va. at 525 and n. 18, 466 S.E.2d at 184 and n. 18. Therefore, “[b]ecause of the ‘liberal thrust’ of the rules pertaining to experts, circuit courts should err on the side of admissibility.” Id.

The Gentry Court stated plainly that [disputes as to the strength of an expert’s credentials ... go to weight and not to the admissibility of their testimony. 195 W.Va. at 527, 466 S.E.2d at 186, citing Daubert, 509 U.S. at 594, 113 S.Ct. 2786 (“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.”). See also Syllabus Point 3, Walker v. Sharma, 221 W.Va. 559, 655 S.E.2d 775 (2007) (“[IJssues that arise as to the physician’s personal use of a specific technique or procedure to which he or she seeks to offer expert testimony go only to the weight to be attached to that testimony and not to its admissibility.”)

As a physician board-certified in internal medicine, with several decades of ex*746perience diagnosing and treating patients with foodborne illnesses, Dr. Gregor meets the minimal educational or experiential qualifications in a field that is relevant to the subject under investigation which will assist the trier of fact. A broad range of knowledge, skills and training qualify Dr. Gregor to offer his opinion regarding the diagnosis and cause of Mr. San Francisco’s illness. Furthermore, Dr. Gregor’s area of expertise covers the particular opinion as to which he seeks to testify. While a physician with a specialization in gastroenterology or epidemiology might, as the appellee wishes, be better qualified to render an opinion on behalf of the appellants, Gentry and Rule 702 do not impose such “overly rigorous requirements of expertise.” Gentry, 195 W.Va. at 524-25, 466 S.E.2d at 183-84. “While the court may rule that a certain subject of inquiry requires that a member of a given profession, such as a doctor, an engineer, or a chemist, be called, usually a specialist in a particular branch within the profession will not be required.” 195 W.Va. at 526, 466 S.E.2d at 185, quoting Charles McCormick, Evidence ¶ 14 at 29 (1954).

Accordingly, we conclude that the circuit eoui't erred in excluding Dr. Gregor’s testimony on the basis that Dr. Gregor was not qualified to offer expert testimony under Rule 702.

Once an expert is deemed qualified, the trial court must address whether the methodology underlying the expert’s conclusion is reliable. The appellants argue that Dr. Gregor’s opinion is reliable under the DaubeH/Wilt analysis, and that the circuit court erred when it excluded the opinion.

The appellants assert that Dr. Gregor’s opinion was farmed through a scientific method called “differential diagnosis.” “Differential diagnosis involves ‘the determination of which one of two or more diseases or conditions a patient is suffering from, by systematically comparing and contrasting their clinical findings.’ ” McClain v. Metabolife Intern., Inc., 401 F.3d 1233, 1252 (11th Cir.2005) (quoting Borland’s Illustrated Medical Dictionary 240 (Douglas M. Anderson et al. ed., 29th Ed.2000)). “Differential diagnosis, or differential etiology, is a standard scientific technique of identifying the cause of a medical problem by eliminating the likely causes until the most probable one is isolated.” Westberry v. Gislaved Gummi AB, 178 F.3d 257, 262 (4th Cir.1999).

The appellants indicate that Dr. Gregor was on staff at Logan General Hospital on May 3, 2002, and treated Mr. San Francisco in the hospital’s emergency room. Dr. Gre-gor noted his patient’s symptoms, particularly noting that Mr. San Francisco vomited 1.8 liters while in the emergency room. After considering his patient’s symptoms and history, Dr. Gregor ruled out various likely causes for the illness after finding no pre-existing gastrointestinal problems, no alcohol use, no peptic ulcer disease and no history of diverticulitis. Dr. Gregor conducted a clinical examination of Mr. San Francisco, reviewed his medical history, his recent travel history, and his food intake history. Taking all of these factors together, Dr. Gregor eliminated various likely causes and concluded that the most probable cause of Mr. San Francisco’s problem was a foodborne illness caused by the allegedly undercooked Wendy’s hamburger. Wfaen asked why he chose the undercooked hamburger as the cause of plaintiffs illness as opposed to other possibilities, Dr. Gregor explained “[i]t’s the highest probability of a series of possibilities.”

The appellee responds by arguing that Dr. Gregor’s opinion is still unreliable and inadmissible. While Dr. Gregor might be trained in the process of deducing a disease based on a set of symptoms and laboratory tests, the appellee argues that Dr. Gregor was essentially speculating about the cause of Mr. San Francisco’s illness. The appellee suggests in its brief, as a factual matter, that there are “more obvious culprits of Mr. San Francisco’s illness” in the foods that Mr. San Francisco ate4 and in the people that Mr. San *747Francisco visited5 in the week preceding his eating of the Wendy’s hamburger. But in answer to the appellants’ legal position, the appellee essentially argues that a differential diagnosis of a particular illness does not necessarily result in a relevant and reliable opinion of the cause of the illness. “The ability to diagnose medical conditions is not remotely the same, however, as the ability to deduce, delineate, and describe, in a scientifically reliable manner, the causes of those medical conditions.” Wynacht v. Beckman Instruments, Inc., 113 F.Supp.2d 1205, 1209 (E.D.Tenn.2000).

In general terms, physicians routinely rely upon differential diagnosis for establishing causation. The overwhelming majority of courts that have addressed the issue have held that a medical opinion on causation based upon a reliable differential diagnosis is sufficiently valid to satisfy the reliability prong of the Rule 702 inquiry. “Most circuits have held that a reliable differential diagnosis satisfies Daubert and provides a valid foundation for admitting an expert opinion. The circuits reason that a differential diagnosis is a tested methodology, has been subjected to peer review/publication, does not frequently lead to incorrect results, and is generally accepted in the medical community.” Turner v. Iowa Fire Equip. Co., 229 F.3d 1202, 1208 (8th Cir.2000).6 In accord, Heller v. Shaw Indus., Inc., 167 F.3d 146, 154-55 (3rd Cir.1999) (noting “that differential diagnosis ‘consists of a testable hypothesis,’ has been peer reviewed, contains standards for controlling its operation, is generally accepted, and is used outside of the judicial context.”).

Even with all the advances of medical science, the practice of medicine remains an art. A properly conducted and explained differential diagnosis is not “junk science.” If a differential diagnosis provides a sufficient basis on which to prescribe medical treatment with potential life-or-death consequences, it should be considered reliable enough to assist a fact finder in understanding certain evidence or determining certain fact issues.

Coastal Tankships, U.S.A., Inc. v. Anderson, 87 S.W.3d 591, 604-05 (Tex.App.2002).

However, while most courts recognize the methodology of differential diagnosis as a scientifically valid way of determining causation, the same courts also warn that opinions based on differential diagnosis must be analyzed on a case-by-case basis, ensuring that the expert’s application of the technique is reliable and proper in each case. As the Eleventh Circuit Court of Appeals explained:

[A]n expert does not establish the reliability of his techniques or the validity of his conclusions simply by claiming that he performed a differential diagnosis on the patient. ... “No one doubts the utility of medical histories in general or the process *748by which doctors rule out some known causes of disease in order to finalize a diagnosis. But such general rules must ... be applied fact-specifically in each case.”

McClain v. Metabolife Int’l, Inc., 401 F.3d at 1253 (quoting Black v. Food Lion, Inc., 171 F.3d 308, 314 (5th Cir.1999)); see also In re Paoli, 35 F.3d at 758 (Differential diagnosis “is a method that involves assessing causation with respect to a particular individual. As a result, the steps a doctor has to take to make that (differential) diagnosis reliable are likely to vary from case to case[.]”)

Thus, an expert’s use of differential diagnosis is reliable and valid only if the expert applied the technique in a manner which is also reliable. “A reliable differential diagnosis typically, though not invariably, is performed after physical examinations, the taking of medical histories, and the review of clinical tests, including laboratory tests, and generally is accomplished by determining the possible causes for the patient’s symptoms and then eliminating each of these potential causes until reaching one that cannot be ruled out or determining which of those that cannot be excluded is the most likely.” Westberry, 178 F.3d at 262 (citation and internal quotation marks omitted).

The elements of a differential diagnosis may consist of the performance of physical examinations, the taking of medical histories, and the review of clinical tests, including laboratory tests. A doctor does not have to employ all of these techniques in order for the doctor’s diagnosis to be reliable. A differential diagnosis may be reliable with less than all the types of information set out above....

Depending on the medical condition at issue and on the clinical information already available, a physician may reach a reliable differential diagnosis without himself performing a physical examination, particularly if there are other examination results available. In fact, it is perfectly acceptable, in arriving at a diagnosis, for a physician to rely on examinations and tests performed by other medical practitioners.

Kannankeril v. Terminix Intern., Inc., 128 F.3d at 807. See also In re Paoli, 35 F.3d at 762 (“[Evaluation of the patient’s medical records is a reliable method of concluding that a patient is ill even in the absence of a physical examination.”) “A differential diagnosis that fails to take serious account of other potential causes may be so lacking that it cannot provide a reliable basis for an opinion on causation. However, a medical expert’s causation conclusion [based on a differential diagnosis] should not be excluded because he or she has failed to rule out every possible cause of a plaintiffs illness. The alternative causes suggested by a defendant affect the weight that the jury should give the expert’s testimony and not the admissibility of that testimony.” Westberry, 178 F.3d at 265 (citation and internal quotation marks omitted).

Differential diagnosis is not a scientific method which lends itself to establishing a direct link between an activity and an illness or injury. Instead, it is a method by which a physician “considers all relevant potential causes and then eliminates alternative causes....” Federal Judicial Center, Reference Manual on Scientific Evidence 214 (1994). It is a process of elimination based upon a study limited to an evaluation of the patient alone.

We therefore conclude that a medical opinion based upon a properly performed differential diagnosis is sufficiently valid to satisfy the reliability prong of the Rule 702 inquiry under Daubert/Wilt. A differential diagnosis is a tested methodology, has been subjected to peer review/publication, does not frequently lead to incorrect results, and is generally accepted in the medical community. Opinions based on differential diagnosis must be analyzed on a case-by-case basis, ensuring that the medical expert’s application of the technique is reliable and proper in each case.

When Dr. Gregor was questioned regarding his opinion as to causation, and why he chose the undercooked hamburger as the cause of the appellant’s illness as opposed to other possibilities, Dr. Gregor explained that “[i]t’s the highest probability of a series of possibilities.” Appellee Wendy’s argues that Dr. Gregor’s differential diagnosis was unre*749liable because he failed to definitively rule out all other potential causes for Mr. San Francisco’s illness. However, we believe that the alternative causes suggested by the appellee affect the weight that the jury should give the expert’s testimony, and not the admissibility of that testimony. See, e.g., McCulloch v. H.B. Fuller Co., 61 F.3d 1038, 1044 (2nd Cir.1995) (recognizing that perceived faults in a doctor’s differential diagnosis are matters for cross-examination that do not affect admissibility); In re Paoli R.R. Yard PCB Litig., 35 F.3d at 764-65 (recognizing that failure to account for all possible causes does not render expert opinion based on differential diagnosis inadmissible; only if the expert utterly fails to consider alternative causes or fails to explain why the opinion remains sound in light of alternative causes suggested by the opposing party is the expert’s opinion unreliable for failure to account for all potential causes).

We therefore conclude that, under a Dau-bert/Wilt analysis, Dr. Gregor’s differential diagnosis of the cause of Mr. San Francisco’s illness is reliable and admissible.

C.

The Admissibility of Dr. Todd’s Testimony

The appellants next argue that the circuit court erred in excluding the testimony of their food safety expert, Dr. Todd, on the basis that his theory was unreliable. Dr. Todd indicated that Mr. San Francisco’s rapid illness was consistent with eating preformed verotoxin produced by E. coli 0157:H7 bacteria in the undercooked Wendy’s hamburger. The circuit court excluded Dr. Todd’s opinion based upon the appellee’s argument that there has, to date, been limited publication or peer review on this subject, and that none of the medical tests performed on Mr. San Francisco at Logan General Hospital — several days after eating the hamburger — found verotoxin or E. coli bacteria.

The appellants argue that Dr. Todd’s theory is logical and is supported by published literature. Based upon Mr. San Francisco’s symptoms, Dr. Todd concluded to a reasonable degree of probability that the cause of Mr. San Francisco’s illness was from preformed verotoxin produced by E. coli in ground beef. To support this, Dr. Todd cited to a study in a journal which found that E. coli sitting in uncooked ground beef can produce verotoxin. Furthermore, the appellants point to Dr. Todd’s wealth of knowledge on the subject of food safety; the record contains Dr. Todd’s cumculivm vitae, which extends for some 77 single-spaced pages.7

The appellees respond that Dr. Todd’s conclusions are not reliable under a Daubert/Wilt analysis. The appellees concede that, in Daubert, Wilt and Gentry, trial judges were admonished that the focus of their reliability analysis must be “solely on principles and methodology, not on the conclusions they generate.” Daubert, 509 U.S. at 595, 113 S.Ct. 2786. See Syllabus Point 2, Wilt (a trial court’s inquiry must assess an expert’s conclusion “by considering its underlying scientific methodology and reasoning.”); Gentry, 195 W.Va. at 523, 466 S.E.2d at 182 (“The problem is not to decide whether the proffered evidence is right, but whether the science is valid enough to be reliable.”).

Still, the appellees contend that “nothing in the Rules [of Evidence] appears to have been intended to permit experts to speculate in fashions unsupported by ... the uncontroverted evidence.” Gentry, 195 W.Va. at 527, 466 S.E.2d at 186 (citation omitted). The appellees assert that Dr. Todd’s opinion is based on assumptions which are speculative and are not supported by the record. For instance, the appellees point out that there are no laboratory results identifying the foodborne organism that caused Mr. San Francisco’s illness. Further, while Dr. Todd’s opinion is based upon a study indicating that meat containing E. coli bacteria can — after four days at a temperature of 98.6 — develop verotoxins, the appellee points out that Dr. Todd presumed in forming his *750opinion that the Wendy’s hamburger was handled under “abusive” manufacturing conditions. In other words, the appellee contends that Dr. Todd speculated that the meat in the Wendy’s hamburger was mishandled,8 and speculated that the meat contained E. coli bacteria, when there is no direct evidence in the record to support that position.

The appellants counter the appellee’s position by arguing that, in proving a food poisoning lawsuit, positive proof by scientific testing is not required. Instead, the appellants argue that “[i]n the absence of direct evidence of the defectiveness of the food, recovery could be supported by circumstantial evidence if every other reasonable hypothesis as to the cause of the plaintiffs illness could be excluded.” Castleberry’s Food Co. v. Smith, 205 Ga.App. 859, 424 S.E.2d 33 (1992). We agree.

To begin, this Court has never required “positive proof by scientific testing to establish a factual basis for medical diagnosis and opinion.” Bussey v. E.S.C. Restaurants, Inc., 270 Va. 531, 537, 620 S.E.2d 764, 767 (2005). Dr. Gregor testified, in his deposition, that Logan General Hospital — a rural hospital — had limited laboratory facilities to test for foodborne illnesses, and that it was not standard medical practice to retain bodily fluids for later testing. As the Bussey court indicated, “food poisoning is a ‘fairly common illness’ for which scientific testing would not be cost effective, and the ‘emphasis is on the last meal before the event.’ ” Id.

The circuit court based its decision to exclude Dr. Todd’s testimony, in large part, upon the fact that his conclusion had not been tested, and that his theory had not been subjected to peer review and publication. Syllabus Point 2, Wilt. However, these factors listed in Wilt are by no means a definitive checklist or test of reliability.. Our review of the record indicates that Dr. Todd sufficiently connected the proposed testimony with the facts of the case. Because food poisoning is a fairly common illness, we see nothing novel in Dr. Todd’s theory that would warrant great interest in its publication. Further, a court may treat an expert’s qualifications as circumstantial evidence that he or she has used a scientifically valid methodology or mode of reasoning in drawing his or her conclusions. Ambrosini v. Labarraque, 101 F.3d 129, 140 (D.C.Cir.1996). Dr. Todd’s extensive background in food safety circumstantially suggests he used a valid methodology in drawing his conclusions. Simply put, we believe that Dr. Todd’s opinion is admissible because he explained precisely how the conclusions were reached, and pointed to an objective source to show that his conclusions were based on a scientific method used by at least a minority of scientists in the field.

We believe that the conflict between the positions taken by the parties regarding Dr. Todd’s conclusions did not render his testimony unreliable, but instead created a jury issue regarding the weight to be given to the testimony. Accordingly, we find that the circuit court erred in excluding Dr. Todd’s testimony.

D.

Order Granting Summary Judgment

Finally, the appellants contend that the circuit court erred in granting summary judgment to the appellees, after excluding both of the appellant’s causation witnesses.

“A motion for summary judgment should be granted only when it is clear that there is no genuine issue of fact to be tried and inquiry concerning the facts is not desirable to clarify the application of the law.” Syllabus Point 3, Aetna Casualty & Surety Co. v. Federal Insurance Co., of New York, 148 W.Va. 160, 133 S.E.2d 770 (1963). “Summary judgment is appropriate where the record taken as a whole could not lead a rational trier of fact to find for the nonmoving party, such as where the nonmoving party has failed to make a sufficient showing on an essential element of the case that it has the burden to prove.” Syllabus Point 4, *751Painter v. Peavy, 192 W.Va. 189, 451 S.E.2d 755 (1994).

The cireuit court granted summary judgment on the basis that the appellants had no evidence of causation, that is, no evidence that the Wendy’s hamburger was the cause of Mr. San Francisco’s illness. Having found that the circuit court erred in excluding both of the appellants’ causation experts, we now find that the appellants made a sufficient showing on an essential element of the case that they had the burden to prove. Accordingly, because it now appears from the record that genuine issues of fact exist to be tried, we find that the circuit court erred in granting summary judgment.

IV.

Conclusion

The circuit court’s order of March 14, 2006 is reversed, and the case is remanded for further proceedings.

Reversed and Remanded.