At the outset, the plaintiffs bear the "burden of establishing, through expert testimony, 'the applicable standard of care.'" Nwaneri, 931 A.2d at 470 (quoting Travers v. District of Columbia, 672 A.2d 566, 568 (D.C. 1996)). "In the District of Columbia, the applicable standard of care in a medical malpractice action is 'a national standard, not just a local custom.'" Id. (quoting Travers, 672 A.2d at 568).

Therefore, the principal issue for our review is whether, in deciding appellees' motion for judgment, the trial court properly determined that the testimony of appellants' expert was unqualified and insufficient to prove the applicable national standard of care. "In a medical malpractice action, the plaintiff carries the burden of establishing . . . `the applicable standard of care, deviation from that standard, and a causal relationship between the deviation and the injury.'" Nwaneri v. Sandidge, 931 A.2d 466, 470 (D.C. 2007) (quoting Travers v. District of Columbia, 672 A.2d 566, 568 (D.C. 1996)). "Because these issues are `distinctly related to some science, profession, or occupation,' expert testimony is usually required to establish each of the elements, except where the proof is so obvious as to lie within the ken of the average lay juror."

In a medical malpractice action, the plaintiff carries the burden of establishing, through expert testimony, "the applicable standard of care, deviation from that standard, and a causal relationship between the deviation and the injury." Travers v. District of Columbia, 672 A.2d 566, 568 (D.C. 1996). In the District of Columbia, the applicable standard of care in a medical malpractice action is "a national standard, not just a local custom."

To establish proximate cause, “the expert need only state an opinion, based on a reasonable degree of medical certainty, that the defendant's negligence is more likely than anything else to have been the cause (or a cause) of the plaintiff's injuries.” Travers v. District of Columbia, 672 A.2d 566, 573 (D.C.1996); see also Perkins v. Hansen, 79 A.3d 342, 344 (D.C.2013).On appeal, the Hospital disputes this conclusion but does so, in our view, chiefly by overstating the plaintiff's burden of proof. It contends that the judge wrongly “shifted the burden of proof on the issue of causation” to the defense (Br. for Appellant at 16) by not recognizing that “[i]t was incumbent on Mr. Willis to prove that the DVT had not yet become ‘well-established’ by September 10th when [the surgeon] entered the order for SCDs” ( id. at 6; italics added).

"The personal opinion of the testifying expert as to what he or she would do in a particular case, without reference to a standard of care, is insufficient to prove the applicable standard of care." Travers v. District of Columbia, 672 A.2d 566, 568 (D.C. 1996). "[I]t is insufficient for an expert's standard of care testimony to merely recite the words `national standard of care.'" Hawes v. Chua, 769 A.2d 797, 806 (D.C. 2001) (citations omitted).

" Furthermore, she faults the trial court for failing to evaluate the defense expert testimony under the standards announced in Frye or Daubert, supra. Although she recognizes that Frye, supra, "addresses the admissibility of expert testimony" (emphasis supplied in original), she contends that the "[ Frye standard] should be used by a trial court sitting without a jury in evaluating expert testimony." In essence, Dr. Abendschein argues that the educational backgrounds and experience of his experts met the requirements of a national standard of care, as explained in Travers v. District of Columbia, 672 A.2d 566 (D.C. 1996). He maintains that Travers does not require "[r]eference to a published standard, if indeed one exists. . . ."

He must testify to a national standard of care to a reasonable degree of medical certainty, and he — moreover, must state the basis for his opinions. . . . In support of his argument, counsel referenced Travers v. District of Columbia, 672 A.2d 566 (D.C. 1996). The trial judge disagreed, saying:

To similar effect, "[t]he personal opinion of the testifying expert as to what he or she would do in a particular case, without reference to a standard of care, is insufficient to prove the applicable standard of care." Travers v. District of Columbia, 672 A.2d 566, 568 (D.C. 1996). No one doubts that the standard of care in this case is beyond the ken of the average layperson.

"In the District of Columbia, the applicable standard of care in a medical malpractice action is 'a national standard, not just a local custom.'" Nwaneri v. Sandidge, 931 A.2d 466, 470 (D.C. 2007) (quoting Travers v. District of Columbia, 672 A.2d 566, 568 (D.C. 1996)). And "the testifying expert must establish that the relevant standard of care is followed nationally, 'either through reference to a published standard, discussion of the described course of treatment with practitioners outside the District at seminars or conventions, or through presentation of relevant data.'"

As noted already, District of Columbia law governs this case. “In a medical malpractice action, the plaintiff carries the burden of establishing, through expert testimony, ‘the applicable standard of care, deviation from that standard, and a causal relationship between the deviation and the injury.’ ” Nwaneri v. Sandidge, 931 A.2d 466, 470 (D.C.2007) (quoting Travers v. Dist. of Columbia, 672 A.2d 566, 568 (D.C.1996)); seeCárdenas v. Muangman, 998 A.2d 303, 306 (D.C.2010) (“Because these issues are distinctly related to some science, profession, or occupation, expert testimony is usually required to establish each of the elements, except where the proof is so obvious as to lie within the ken of the average lay juror.”) (quoting Washington v. Washington Hosp. Ctr., 579 A.2d 177, 181 (D.C.1990)) (internal quotation marks omitted).