The Supreme Court established in Daubert v. Merrell Dow Pharmaceuticals that scientific testimony must (1) rest on a reliable foundation; and (2) be relevant to the task at hand to be admissible under Federal Rule of Evidence 702. The Court in Daubert provided a non-exhaustive set of factors that trial courts consider when determining whether scientific testimony is reliable. (These factors include whether the witness's “theory or technique ... can be (and has been) tested”; whether it “has been subjected to peer review and publication”; its “known or potential rate of error”; “the existence and maintenance of standards controlling the technique's operation”; and whether it has attracted “[w]idespread acceptance” within a relevant scientific community.)
What if, however, the scientific testimony is broadly reliable but not precise?
The Ninth Circuit addressed this question in United States v. Baker. In relevant part, Baker concerned the admissibility of cell site location information (CSLI). At trial, the government proffered the testimony of a CSLI expert, who explained how information about the cell towers to which the defendant’s phone connected on the evening of a robbery allowed him to “discern the phone's movement toward the [crime scene] before the robbery and away from it afterward.”
However, the expert informed the jury that CSLI showed only that the defendant’s phone moved from one area of Los Angeles to the general area of the crime scene at the approximate time that the crime occurred, and could only identify where a phone was “in a general sense.” Ultimately, the CSLI was admitted over the defendant’s motion to suppress, and the defendant was convicted.
On appeal, the defendant argued that the court abused its discretion by admitting the testimony because neither the court nor the government “appropriately circumscribed the import of the historical cell tower data by explaining that CSLI shows a phone's location within a range rather than pinpointing it exactly.” The Ninth Circuit disagreed, holding that the evidence was admissible because the expert witness adequately informed the jury of the limitations of CSLI and even confirmed those limitations explicitly on cross examination.
Baker provides much-needed guidance for attorneys and courts faced with scientific evidence that might meet the traditional Daubert standard of reliability, but is nonetheless imprecise. Critically, juries must be made aware of the limitations of the evidence; a mere limiting instruction to the jury that it need not credit the evidence would likely be insufficient. Instead, attorneys must elicit testimony as to the imprecision of the evidence. Then, the trier of fact has the information required to give the testimony proper weight and use it to aid in reaching a verdict.
Scientific evidence can be an important bow in an attorney’s quiver. That evidence must be relevant and reliable under the Daubert standard, but it is not strictly necessary that it be definitive or precise. However, the attorney presenting the evidence must be fully aware of its limitations and able to explain those limitations to the trier of fact.
