7: Expert witnesses Flashcards
Reasonable reliance
An expert’s opinion may be based on facts and data that the expert has personally observed or about which the expert has been made aware.
When such facts and data are not admissible, the opinion itself may nevertheless be admissible if experts in the particular field would reasonably rely on those kinds of facts and data in forming an opinion on the subject.
Reliability
An expert opinion need only be:
(i) based on sufficient facts or data, and
(ii) the result of reasonably relied-upon methods or principles
(iii) reliably applied to the facts in the case.
Mental state of a criminal defendant
An expert may not state an opinion about whether a criminal defendant had the requisite mental state of any element of the crime charged or of a defense. That determination lies in the province of the trier of fact.
Underlying data
An expert may state an opinion and give the reasons for the opinion without first testifying as to the underlying facts or data.
Admissibility of expert testimony
Before an expert witness may testify, the court must first determine that the subject matter of the witness’s testimony:
(i) is scientific, technical, or other specialized knowledge, which focuses on the reliability of the testimony; and
(ii) will help the trier of fact understand the evidence or determine a fact in issue—i.e., that the testimony is relevant.
Impeachment
A party can challenge the credibility of an expert witness on cross-examination by attacking the adequacy of the expert’s knowledge, both with respect to:
- their general knowledge in their field of expertise; and
- their specific knowledge of the facts underlying their testimony.
An expert is subject to cross-examination on her experience and knowledge even after being qualified as an expert.
Demonstrations and experiments
A court may allow demonstrations and experiments to be performed in the courtroom, but they may be excluded if they will result in an undue waste of time or confusion of the issues.
