The customary care standard in medical malpractice litigation is generally established through the testimony of physicians who are considered experts in the field relating to the specific malpractice case. In general, expert testimony must establish that it is more probable than not that the defendant’s act of negligence was responsible for the resulting harm. In Daubert v. Merrell Dow Pharmaceuticals Inc., the Supreme Court determined that an expert must rely on more than just their opinion to define customary care standards. The Court held that expert testimonies must satisfy two additional requirements: (1) the evidence presented must be shown to constitute scientific knowledge, and (2) the evidence must be relevant to the case in question.
The role of expert witnesses in defining the customary care standard is controversial. The Supreme Court’s “scientific validity” directive creates a dangerous legal loophole in which expert witnesses may cite to any scientific evidence regardless of custom. Plaintiffs could make a submissible case based on an expert testimony explaining the alternative courses of treatment that were available and were not prescribed. Without explicit standards, the expert can choose any scientifically based treatment with a superior risk to benefit ratio and testify as to why the course chosen by the defendant was unreasonable.
Additionally, agreement between physicians is widely variable when determining which treatment is appropriate. When considering liability events, physician reviewers only achieve moderate levels of agreement on whether an adverse event was due to medical management or the disease process, and low levels of agreement on whether the care in question was negligent. Subsequently, identifying the key “customary” component in the legal standard becomes dubious because physicians cannot reliably identify how other physicians make decisions. In one study, physicians reviewed an abstract that described how a patient presented to the defendant-physician in a medical malpractice case. Only 36% of these physicians could accurately estimate the behavior of other physicians.
Dr. David Eddy wrote,
“When an expert answers a question about a community standard it is extremely unlikely that he or she has any real data on actual practices. It is far more likely that what an expert believes is the practice in a community is what the expert personally believes should be the standard of care. … You don’t have to hire an expert to lie. You can just find one who truly believes the number you want.”
Asking these experts to “help” the jury define the standard of care and determine whether it was met is disingenuous. And the average medical liability case involves no fewer than five expert witnesses.
Professor Michael Green noted:
“The selection process for expert witnesses, forged in the crucible of the adversarial system, tends to produce experts who are polished and persuasive but not necessarily the most committed to accuracy or the most knowledgeable in their field. The experts who testify at trial are unlikely to reflect a random sample of scientific opinion or provide the jury the most accurate assessment of it. … [T]he adversarial system encourages parties to take extreme positions that often are unhelpful to the jury in sorting out the truth.”
In practice, most courts are willing to play only a very limited “gate-keeper” role, rejecting only that evidence that is clearly without scientific basis. As long as the “expert” physician has documented qualifications within his or her area of specialty and the evidence offered is not obviously lacking scientific basis, courts will leave most decisions about strength of evidence and standards of practice up to a jury. Thus, physicians are at the mercy of lay jurors who have little or no medical background beyond what the expert witnesses have told them, and are often sympathetic to those injured by the alleged malpractice.
 Strauss, D., What Does the Medical Profession Mean By “Standard of Care?”, http://jco.ascopubs.org/content/27/32/e192.full#xref-ref-2-1, (last visited February 23, 2015).
 Richard L. Wiener, A Psycholegal and Empirical Approach to the Medical Standard of Care, 69 Neb. L. Rev. 115 (1990).
 Daubert v Merrell Dow Pharmaceuticals, 509 U.S. 579, 589 (1993).
 Id. at 163-170
 Eric J. Thomas et al., The Reliability of Medical Record Review for Estimating Adverse Event Rates, 136 Annals Internal Med. 812 (2002).
 Arthur Hartz et al., Physician Surveys to Assess Customary Care in Medical Malpractice Cases, 17 J. Gen. Internal Med. 546 (2002).
 Medical Guesswork, John Carey, http://www.bloomberg.com/bw/stories/2006-05-28/medical-guesswork, (last visited February 23, 2015).
 See generally Douglas A. Boenning et al., The Pediatrician as Expert Witness: Participation and Reaction to This Activity, 146 AM. J. DISEASES CHILD. 1107 (1992); Samuel R. Gross, Expert Evidence, 1991 WIS. L. REV. 1113, 1113-25, 1130 (1991).
 The Expert Witness in Medical Malpractice Litigation: Through the Looking Glass, James C. Johnston, MD, JD, et al., http://www.bmpllp.com/files/jcn_expert_witness_article_2.pdf, (last visited February 23, 2015).
 James T. Richardson, Bendectin and Birth Defects: The Challenges of Mass Toxic Substances Litigation, by Michael D. Green. University of Pennsylvania Press, 418 Services Drive, Philadelphia, Pa. 19104. 1996, 81 Judicature 86, 87 (1997)
 Does Practicing Evidence-Based Medicine Increase Your Risk of Being Sued?, James Eagan, JD, http://www.academicins.com/articles/Evidence-based_medicine.pdf, (last visited February 23, 2015).