One or more of its variants appears in the vast majority of expert reports and transcripts for expert testimony on medical causation: “reasonable degree of medical/scientific certainty/probability.” Sometimes, it is attached as a seeming exclamation point at the end of direct testimony of an expert at trial with an exchange like “Were all of your opinions here held to a reasonable degree of medical certainty?” and “Yes, they certainly were.” What does “reasonable degree of medical certainty” mean? Does it mean something different than “reasonable degree of medical probability”? If “certainty” means 100% and “probable” means more than 50%, then why are the words “reasonable degree” included in these phrases? We leave the surveys and exposition of research dating to the 1907 Esso v. Teric case to Bexis and will simply offer that most experts, lawyers, and judges use these phrases reflexively, without pondering their meaning. Clearly, “reasonable degree of medical certainty” plays some role in distinguishing guesswork from something on which a jury can place weight when deciding cases. These words also come from substantive law and operate independent of the familiar procedural requirements of things like Fed. R. Evid. 401-403 & 701-03 and Daubert. Independence means that expert opinion on medical causation could pass the “certainty” requirement and still not be sufficiently probative and reliable to be admitted, which happens all the time. The flip side is rarer, where expert testimony that passes Daubert
might still fail because it is not sufficiently certain for state law.
Rare defines the situation in Valido-Shade v. Wyeth LLC, MDL No. 1203, Civ. No. 12-20003 (E.D. Pa. Nov. 3, 2014), slip op., in a number of respects. The case is part of the diet drug litigation, which is heading toward its third decade, a rarity among single target litigations. The injury claimed is pulmonary arterial hypertension, which occurs rarely in the general population–at least actual PAH does. The particular plaintiff claimed to have been diagnosed with PAH in 2010 after using the drugs in 1996 and 1997. Although not really explained in the opinion, the reference to “such a long latency period” means that the plaintiff was apparently asymptomatic for the vast majority of the 13 years from last use to diagnosis. If she had been otherwise, given the ruling in Mingus v. Wyeth, MDL 1203, No. 04-23744, 2006 WL 1050289, *3 (E.D.Pa. Apr. 20 2006), then the plaintiff may have been...
