In Expert Witnesses and Reports, Manuel Lopez and David Chaumette of Shook, Hardy & Bacon L.L.P. write on when the expert testimony does not fit the case:
The expert testimony must also “fit” the facts of the case. That is, the expert must testify about scientific theories that have a direct impact the case at hand. One interesting case-where the Court of Appeals rejected a challenge to an expert based on lack of “fit”-was the decision in Gigliobianco v. State, 179 S.W.3d 136, 141-42 (Tex. App.-San Antonio 2005) aff’d, 210 S.W.3d 637 (Tex. Crim. App. 2006). Gigliobianco involved an allegation of drunk driving. The state submitted breath test results that the police took some time after the arrest. The Defendant objected that the results should have been excluded under Rule 702 “in the absence of retrograde extrapolation proving his alcohol content at the time he drove.” Id. at 141. Without such an analysis, he argued, “the State’s expert’s testimony did not ‘fit’ the facts of the case because the expert did not know … his alcohol content when he drove.” Id. The Court acknowledged the “fit” requirement: “Expert testimony must be sufficiently tied to the facts to meet the simple requirement that it be helpful to the jury.” Id. at 142 (citations omitted). But the Court still found that the evidence was relevant and admissible. Id. (“the intoxilyzer test results and the expert testimony were properly admitted because ‘they are pieces in the evidentiary puzzle for the jury to consider in determining whether [defendant] was intoxicated at the time he drove.'”