Evidence Foundations 8 - Lay and Expert Witness Testimony

Things and documents offered as evidence must be authenticated.
The person offering the evidence must prove its authenticity (e.g., "This is the contract signed by the party").
Authentication is usually done through witness testimony.

Witnesses are presumed competent unless proven otherwise.
Federal court requirements for witness competency:
- Personal knowledge of the facts they're testifying about.
- An oath to tell the truth.

Lay witness: A regular person, not an expert.
Lay witnesses generally cannot give opinion testimony; they must stick to the facts.
The Trier of fact draws conclusions based on facts presented.
Exception: Lay witnesses can give opinions if:
- The opinion is rationally based on the witness's perception.
- The opinion is helpful to the trier of fact.
- The opinion is not based on scientific, technical, or specialized knowledge.
- Rationale: Avoids a flat ban on opinion testimony, acknowledging some opinions are inherently factual.

General appearance, condition, or emotion of a person (e.g., "David looked tired").
Matters of sense recognition (e.g., "He smelled like flaming hot Cheetos").
Voice or handwriting recognition (e.g., identifying handwriting in a letter).
All examples based on personal observation and provide unique insights.

Permitted: A lay witness testifies that David looked ill after eating salami roses.
Not Permitted: A lay witness testifies the salami roses were contaminated with E. coli; this requires expert testimony.

Experts can give opinions, even without direct personal knowledge of the incident.
Expert witnesses are often paid.
Expert testimony is allowed when scientific, technical, or specialized knowledge helps the trier of fact.
The testimony must pass rules ensuring relevance and reliability.

Trial court acts as gatekeeper for scientific evidence, reviewing it in a pretrial hearing (Daubert Hearing) outside the presence of the jury.
Ensures that juries are not swayed by "quackery or charlatanism."

Would the scientific, technical, or specialized knowledge help the fact finder?
Is the expert qualified based on knowledge, skill, experience, training, or education?
Is the testimony based on sufficient facts or data?
Did the expert use reliable principles and methods?
Were those principles and methods reliably applied to the facts of the case?

Qualified Expert: Includes those with knowledge, skill, or experience.
- Example: A dog walker with 10 years of experience can give an opinion on walking French Poodles.
Sufficient Facts or Data: Can be from the expert's personal observation or facts made known to the expert at or before trial.
- Facts supplied to the expert outside the courtroom must be of a type reasonably relied upon by experts in the field.
Reliability of Principles and Methods: The court reviews:
- Whether the theory or technique has been tested.
- Whether it has been subjected to peer review and publication.
- The known or potential rate of error.
- Whether it's generally accepted by experts in the same field.
Standard of Proof: All factors must be proven by a preponderance of the evidence.
- If proven, the jury hears the expert testimony;
- If not, the judge excludes the testimony.

Experts can give an opinion on the ultimate issue in a case.
- Example: A brain surgeon can testify that another brain surgeon failed to use reasonable care.

In criminal cases where the defendant's mental state is an element of the crime or defense (e.g., insanity plea), the expert cannot give an opinion on the defendant's mental state.