Evidence: Whether evidence is sufficiently reliable to admit under OEC 702 requires an expert to explain what his or her expertise is, how the information is gathered, how the information is used in reaching his or her conclusion, and what scientific basis supports each step of that process.

Defendant was convicted of second-degree assault, third-degree assault, and first-degree criminal mistreatment for injuries his girlfriend’s young son sustained while in Defendant’s care. The State’s expert physician testified that the child was abused, and that Defendant was the perpetrator. The Court of Appeals affirmed the convictions, and the Supreme Court granted Defendant’s petition for review. Defendant contended that the trial court erred in admitting testimony from the State’s expert physician, identifying Defendant as the perpetrator. The Supreme Court held that this evidence was not admissible under OEC 702 because the physician did not establish that she was an expert at identifying perpetrators of abuse, nor did she explain how any of the injuries alone indicated that Defendant caused them. Defendant argued that the child’s aunt caused the skull fracture, which was the only injury that qualified as creating a “substantial likelihood of death,” required for second-degree assault. The physician’s inadmissible testimony dealt with the heart of Defendant’s factual theory of the case. The Court also found that the physician’s inadmissible testimony could have influenced the other convictions and held that this error was not harmless because it was likely to influence the verdict. Reversed and remanded.