lames Nucor for not explaining how these ambiguities would affect Plaintiffs' statistical accuracy. Maj. op. at 22. That burden was not Nucor's. Cf. Cooper v. Smith & Nephew, Inc., 259 F.3d 194, 199 (4th Cir. 2001) (noting that the "proponent of the testimony" bears the burden of proving that it is reliable). Rec