Gatekeeping is the judicial task to assure that expert testimony is not only relevant but reliable. Recently, Judge Kaplan once again issued an informative Rezulin opinion.2 This one clarifies the interface in toxic tort cases between general and specific causation and so-called "differential diagnosis." Our prior columns have examined the difficulty in over-crediting a differential diagnosis as a causation reliability godsend.3 After all, while this diagnostic technique certainly has value in clinical medicine, where treatment of the patient presenting symptoms is a temporal priority, i.e., something perhaps has to be done — the causation inquiry in the courtroom is, instead, a search for the truth, not guesswork. As we suggested in a prior article reviewing older case law, let's say a patient presents himself with a set of symptoms, chest pain for example. In order to establish an appropriate course of treatment — sometimes needed right away — the doctor considers all possible causes of chest pain, obtains as much information as is feasible (via an interview, examination and tests, etc.) and then eliminates the possible causes to find the likely one. The process works vitally in clinical practice because time may be of the essence, a choice of treatment is necessary and action has to be taken. If the diagnosis is wrong, that is, if the process of elimination concluded the wrong cause of the symptoms, follow-up on the patient often can disclose that fact. Another diagnosis can be made and the course of the patient's treatment altered. What may be vital practice for much of clinical medicine, however, is not necessarily the best tool for use in the courtroom where inspired guesswork or creative hunches amount to little more than the proverbial "speculation and conjecture" which the law repudiates. The courtroom battle is not over treating the patient, who presents to the treating doctor as a flesh-and-blood being in need of timely assistance, but over the search for the truth, at least that which is more probable than not. In the trial setting, if the expert's differential diagnosis were unreliable and wrong, the jury or court may make the wrong decision on liability with no practical redress in the factual battle of the experts. That the mere right of cross-examination is no solution for it simply confirms the factual battle. Cross-examination does not satisfy the gatekeeping objective which is to keep out unreliable testimony altogether. If a physician considers 15 possible causes of a patient's painful symptoms and wrongfully eliminates five of them, yet the patient recovers, either because the doctor guessed correctly or because the patient's own immune system eventually "cured" the problem, the erroneous part of the expert's process of elimination has limited practical consequence. The physician's inspired hunch or intuitive guess might have been correct. But, if the question at a trial is whether a particular chemical caused a plaintiff's set of symptoms and the expert's differential diagnosis wrongfully has eliminated five out of 15 possible causes, should that testimony be allowed as reliable? Is not the opinion in the category of a mere hunch? Is it not speculative? What if one of the five eliminated causal agents were the real culprit? Has justice been served? Has the search for the truth been satisfied?4 Scrutiny Required Thus, when the clinical diagnostic technique is used in the courtroom, closer scrutiny seems to be called for in order to establish reliability of the causation opinion. One should ask whether the diagnostic method and other underpinnings for the expert's opinion satisfy Daubert's reliability criteria. Is the diagnosis supported by hard science? Merely incanting the magic words "differential diagnosis" does not, and should not, make reliability of the opinion a shoo-in. In In re Rezulin Product Liability Litigation, the decedent's hepatic failure was caused by cirrhosis. Plaintiff attributed this to ingestion of Rezulin. The defendant manufacturer moved for summary judgment challenging plaintiff's ability to prove general causation. Plaintiff countered with a declaration by a board-certified gastroenterologist concluding, with a reasonable degree of medical certainty, that decedent's liver disease was caused by taking Rezulin. Yet, in his deposition, the highly qualified internist could not cite any published studies finding that Rezulin causes cirrhosis or that the drug can exacerbate or accelerate pre-existing liver disease. Judge Kaplan observed that toxic tort causation has two components: general and specific. The former involves demonstrating that a substance is capable of causing a particular injury or condition in the general population. Thus, frequently, claimants try to show, through a review of scientific and medical literature, that a substance can cause a particular disease. Specific causation, on the other hand, addresses the question whether a substance caused a particular individual's injury, i.e., was a given exposure of the substance the cause of plaintiff's disease? A claimant must establish both causation components to prevail. Obviously, reliable expert proofs usually will be critical on these issues. The court reviewed the now-familiar Daubert criteria of expert reliability and found that the gastroenterologist's testimony "fell far short."5 The expert's basis for his opinion "was the generalization that he had seen unspecified studies that, in his view, supported the proposition that Rezulin causes liver failure and death." But here it was undisputed that the deadly liver failure was caused by cirrhosis. Yet, no studies or other proof was offered to suggest that cirrhosis could be caused or exacerbated by the drug. Specific Causation Plaintiff suggested that the expert had relied on his review of the decedent's medical records and, therefore, the opinion was admissible. Judge Kaplan, somewhat generously, construed this argument as a claim of admissibility because the opinion resulted from a differential diagnosis. The basics of this methodology were reviewed. It is a "patient-specific process" in which physicians try to identify "the most likely cause of a set of signs and symptoms from a list of possible causes." The physician first "rules in" all scientifically plausible causes of plaintiff's injury. Then he or she "rules out" the least plausible causes until the most likely cause remains. A fundamental assumption of this method is that the final, suspected cause "must actually be capable of causing the injury." In other words, the expert must "rule in" the suspected remaining cause as well as "rule out" the other possibilities.6 Judge Kaplan clarified, however, that differential diagnosis "does not 'speak to the issue of general causation. [It] assumes that general causation has been prove[d] for the list of possible causes' that it rules in and out in coming to a conclusion."7 The court acknowledged that a Connecticut district judge in the Perkins case8 seems to have concluded that "[d]ifferential diagnosis is a reliable basis to prove general causation in this circuit," relying principally on the U.S. Court of Appeals for the Second Circuit's McCullock decision in 1995.9 But a review of McCullock does not bear that out. The circuit there "merely registered its approval of the expert's reliance on a variety of sources to arrive at an opinion as to both general and specific causation." It is not at all clear that the McCullock court regarded differential diagnosis as probative of general causation. In any event, the trial judge retains discretion to reject an expert's general causation opinion based on an unreliable differential diagnosis. The Rezulin case illustrates the "fundamental problem" with differential diagnosis (even assuming the expert in fact had relied on it). The doctor simply did not offer any reliable basis for concluding that Rezulin is capable of causing the cirrhosis that caused the liver failure that resulted in the death. "In other words, the doctor offered no reliable ground upon which the drug may be "ruled in" as a plausible cause of the cirrhosis. Although the expert's qualifications and good faith were not in question and, possibly, time and medical research will prove him right, nevertheless Daubert requires much more: the opinion must rest on sufficient facts and data; and it must be the product of reliable principles and methods properly applied to the facts of the case. None of these admissibility criteria were satisfied. Accordingly, the motion for summary judgment was granted. 'Floating Wheel' Case Unreliable causation testimony can doom not only toxic tort claims but also mechanical design or manufacturing defect cases. A decision issued by the Texas Supreme Court only on Dec. 31 illustrates this well in a hard-fought automobile products liability case spanning two trials and multiple appeals. The new decision is Volkswagen of America Inc. v. Ramirez,10 a case in which this writer and others in his office represented the automotive defendant. The Texas High Court opinions are informative even to counsel outside the Lone Star State for they employ quintessential Daubert analysis. Further, some colorfully instructive language by Justice Nathan L. Hecht is added in a concurring opinion. The facts in a nutshell were as follows. A 1996 Volkswagen was bumped by a Camaro heading in the same direction. The driver of the Volkswagen lost control, immediately crossed the median and collided nearly head-on with a Ford Mustang in the opposing roadway. Occupants of the Mustang were injured and killed. Their representatives sued alleging that the left rear wheel of the Volkswagen disengaged due to defects and caused loss of control. The wheel assembly, however, was found completely detached from the car's stub axle, positioned directly under the left rear wheel well. This did not square with plaintiff's theory of a separated wheel back on the original roadway. Defendant contended that the wheel detached as a consequence of the accident. The first trial resulted in a defense verdict. The trial judge, however, granted a new trial specifying no reasons other than "in the interests of justice," apparently a nonreviewable determination under Texas law.11 The second trial resulted in a plaintiff's verdict followed by defendant's appeal. Plaintiff's experts were an accident reconstructionist and a metallurgist. The latter claimed various metallurgical defects caused the wheel to separate. Given the position of rest of the detached wheel, plaintiff's reconstructionist had to opine that the wheel disengaged on the roadway but stayed tucked underneath as the car entered and fishtailed across the grass and concrete median at 50 to 60 mph and during the collision. This "floating wheel" theory was rationalized by reliance on the "laws of physics." None of the justices were fooled. After typical Daubert analysis, the court found the purported "laws of physics" explanation insufficient. There was no objective scientific analysis, only the expert's subjective interpretation of the facts. The opinion was deemed unreliable and constituted no evidence of causation. The metallurgist's snippet of causation testimony, conclusory on its face, could not fill the gap in proof. First, the metallurgist had relied on the reconstructionist's unreliable analysis. Second, he could not explain the "crucial question" — how the floating wheel stayed in the wheel well throughout the high-speed movement of the car and its collision with the Mustang. The court held 6-2 that judgment should be entered for defendant. Two justices dissented asserting that the metallurgist's testimony was sufficient to warrant a new trial. Justice Hecht, who joined fully in the court's opinion, added a brief response to the dissent. While the metallurgist spoke of microscopic thread tearings with loose nuts, false brinell marks and metal fragments with temperature inconsistencies, there was only one thing to connect his observations with his conclusions and that was "his own say-so." No Wool Over Laymen's Eyes The validity of his conclusions could not be measured by objective tests, only by his personal credibility. But, said Justice Hecht, "we require more of an expert witness, lest a very convincing charlatan in a lab jacket pull the wool over laymen's eyes." A claim will not stand or fall on the mere ipse dixit of a credentialed witness. "It is not enough that an expert seem credible. He must show that his views have the support of established objective observations or a well-considered consensus of at least a substantial segment of the scientific, technical or specialized community to which he belongs." This expert did neither. To make his point emphatically, Justice Hecht offered the following memorable thoughts: The dissenting Justices would surely never allow me to testify that I have degrees from distinguished universities, that I have long been interested in aberrant behavior, that I have access to an electron microscope, that I have studied the dissenting Justices' DNA, and that they are, sad truth to tell, extraterrestrials. Even if all of the premises were true (some are not), my colleagues in dissent would have a powerful argument that the only bridge between my credentials, experience, and observations on one side, and my opinions on the other, is my own veracity, which is not enough. Such opinions cannot rest on mere belief convincingly expressed. They provide no support for a proposition over which other experts like myself may disagree, leaving the matter for a jury to decide. Such opinions are no legal evidence at all. Moreover, disregarding unreliable expert opinions is not reweighing the evidence: One cannot reweigh evidence that weighs zero. Michael Hoenig is a member of Herzfeld & Rubin Endnotes:________________________________________________________________________________________________________ 1. Hoenig, " 'Gatekeeping' of Experts: The New 'Compurgators,' " The New York Law Journal, July 12, 2004, p. 3. 2. In Re Rezulin Product Liability Litigation (MDL No. 1348), NYLJ, Dec. 17, 2003, p. 28 (SDNY 2004). 3. Hoenig, " 'Gatekeeping' And Differential Diagnosis," NYLJ, Dec. 11, 2000, p. 3. 4. Id. 5. Rezulin Litigation, supra n. 2, NYLJ, Dec. 17, 2004, at p. 28, col. 2. 6. Id. 7. Id. (quoting and citing abundant case law). 8. Perkins v. Origin Medsystems, Inc., 299 FSupp2d 45, 57 (D. Conn. 2004). 9. McCullock v. H.B. Fuller Co., 61 F3d 1038 (2d Cir. 1995). 10. No. 02-0557 (Texas Sup. Ct. Dec. 31, 2004). 11. See In re Volkswagen of America, Inc., 22 S.W. 3d 462 (Tex. 2000) (dissent to denial of petition for writ of mandamus). |
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