Also known as: scientific evidences
Written by attorneys · grounded in primary & secondary sources — see below
Evidence derived from scientific methods or expert analysis that a court evaluates for relevance and reliability before admission. Reliability turns on whether the underlying theory or technique has been tested, subjected to peer review, shown to have a known error rate, governed by standards, and generally accepted in the field.
Scott Summers sued a chemical manufacturer after developing a rare blood disorder. He offered an expert who linked the disorder to the plant's emissions based on animal studies and a proposed cellular mechanism. The district court examined whether the expert's leap from high-dose animal data to human therapeutic exposure satisfied reliability standards and excluded the testimony when the gap proved too wide.
Sofia Stern sued a tire company after a blowout caused her car to crash. She offered an engineer who concluded the tire was defective based on visual inspection and experience. The court applied the same reliability inquiry used for scientific evidence and excluded the opinion when the methodology lacked testing or peer review.
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Steven Silva sued manufacturers after developing lung cancer he attributed to workplace PCB exposure. His experts relied on animal studies and structure-activity analysis to claim promotion of cancer. The district court found an analytical gap between the data and the specific causation opinion and excluded the testimony.
Simon Stern was convicted after the prosecutor commented on his silence. The state argued any error was harmless because other evidence, including forensic lab results, was overwhelming. The court assessed whether the scientific evidence alone could sustain the verdict beyond a reasonable doubt.
Samantha Stone faced a death sentence for a crime committed at age seventeen. She introduced brain-imaging studies showing incomplete prefrontal development in adolescents. The court weighed whether this scientific evidence established a categorical bar on capital punishment for juveniles.
Selena Singh was identified in a show-up after a robbery. She sought to introduce expert testimony on the unreliability of cross-racial identifications under stress. The court considered whether the scientific research on eyewitness memory met reliability thresholds for admission.
Federal Rule of Evidence 702 requires the trial judge to act as gatekeeper and ensure the testimony is both relevant and reliable. Reliability is assessed flexibly by considering whether the theory has been tested, peer-reviewed, shown to have a known error rate, controlled by standards, and generally accepted.
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Appellate courts review the ruling for abuse of discretion. The deferential standard applies even when the exclusion leads to summary judgment and even in technically complex toxic-tort cases.
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Due process requires disclosure of material favorable evidence regardless of whether the defense requests it and regardless of the prosecutor's intent. Lab results supporting an accidental-contamination theory are material when they could reasonably affect the verdict.
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…(9th Cir.1992). The standard for admissibility of expert testimony in this circuit at the time was the so-called Frye test: Scientific evidence was admissible if it was based on a scientific technique generally accepted as reliable within the scientific community. Frye v. United States , 293 F. 1013, 1014 (D.C.Cir.1923).[^maj-2]…