The evidence is sufficient to establish proximate cause if the expert states 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. Robinson v. Group Health Ass'n, 691 A.2d 1147, 1150 (D.C. 1997) (internal brackets and quotation marks omitted) (citing in part W. PAGE KEETON, et al., PROSSER AND KEETON ON THE LAW OF TORTS 41, at 269 (5th ed. 1984), for the principle that the plaintiff "must introduce evidence which affords a reasonable basis for the conclusion that it is more likely than not that the conduct of the defendant was a cause in fact"). The "more likely than not" standard is firmly embedded in our law. See Talley v. Varma, 689 A.2d 547, 553 (D.C. 1997); Lasley v. Georgetown Univ., supra note 4, 688 A.2d at 1387; Travers v. District of Columbia, 672 A.2d 566, 570 (D.C. 1996); Carmichael v. Carmichael, 597 A.2d 1326, 1330-31 (D.C. 1991); Psychiatric Inst. of Washington v. Allen, 509 A.2d 619, 624 (D.C. 1986); Gordon v. Neviaser, 478 A.2d 292, 296 (D.C. 1984). and see Twyman v. Johnson, 655 A.2d 850, 852-54 & n.5 (D.C. 1995); District of Columbia v. Freeman, 477 A.2d 713, 716 & n.9 (D.C. 1984) (both applying the "more likely than not" test of causation outside the medical malpractice context). Illustrating application of this principle is our decision in Talley v. Varma, supra, in which the plaintiff sued her physician for near-total loss of her sense of taste after he had treated her with radiation to remove thyroid tissue that remained following previous surgery to remove her cancerous thyroid gland. "Medical testimony as to the mere possibility of a causal relation," we stated, "is not sufficient." Id. (internal citation marks omitted), quoting Sponaugle v. Pre-Term, Inc., 411 A.2d 366, 368 (D.C. 1980), and citing Quick v. Thurston, 110 U.S. App. D.C. 169, 172, 290 F.2d 360, 363 (1961) (testimony that "there were two possible theories as to source of [plaintiff's] infection," one entailing negligence and the other not, was insufficient to create a jury issue on proximate causation).