Lay & Expert Opinion (Rules 701-705 / Daubert)
Evidence · Lesson 08
Lay & Expert Opinion (Rules 701-705 / Daubert)
這一課問的是：本意見是否得以一般或專家證言採用？
ActorActObjectStandardConsequence
Issue · what this lesson is really about
Is the opinion admissible as lay or expert testimony?
這一課問的是：本意見是否得以一般或專家證言採用？
Trigger words & phrases that should flag this issue:
expertopinionscientificultimate issuespecialized
Core Terminology · 7 must-know
Tap a card to flip and reveal the meaning.
Rule 701
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Lay opinion: rationally based on perception + helpful.
701 一般意見。
Rule 702
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Expert testimony if specialized knowledge will help and reliable.
702 專家證言。
Daubert
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Reliability factors: tested, peer review, error rate, general acceptance.
Daubert 可靠性。
Frye
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Older test: general acceptance in field.
Frye 舊測試。
Rule 703
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Expert may rely on inadmissible data if reasonable in field.
703 依賴。
Rule 704
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Opinion on ultimate issue generally not objectionable.
704 終局議題。
Rule 705
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Expert may give opinion without disclosing underlying data.
705 不必先揭。
Rule Sentence · the workhorse
Lay opinion under Rule 701 requires the opinion to be rationally based on the witness's perception and helpful to the trier of fact; expert opinion under Rule 702 requires specialized knowledge that will help the trier and is reliable under the Daubert factors.
Sentence Anatomy · 5 roles, 5 colors
Every rule sentence breaks into five visual roles.
Actor 行為人witness證人
Act 行為offering opinion提出意見
Object 對象fact at issue系爭事實
Standard 法律標準701 (lay) or 702 (expert) + Daubert701 / 702 + Daubert
Consequence 後果admitted or excluded採用或排除
Casebook Snapshot · a real American case
Daubert v. Merrell Dow Pharmaceuticals
Holding. Rule 702 imposes a special obligation on the trial judge to ensure that scientific testimony is not only relevant but reliable. The judge serves as a gatekeeper, considering factors such as whether the theory has been tested, peer-reviewed, has a known error rate, and is generally accepted in the relevant scientific community.
Why it matters. Daubert replaced Frye's pure general-acceptance test with a flexible reliability inquiry — and made trial judges the gatekeepers.
Daubert：法官為閘門人；可靠性以多因素判斷。
Common Mistakes · what trips students
✗ Frye 仍為聯邦標準。
✓ Daubert replaced Frye in federal courts.
Daubert 取代 Frye。
✗ lay opinion 不能就 ultimate issue 發表。
✓ Rule 704 generally allows it.
704 通常允許。
Mini IRAC · build the Application
Issue. Should the court admit Dr. X's expert testimony, based on a new biomechanics theory not yet peer-reviewed, on the cause of a back injury?
Rule. Under Rule 702 and Daubert, expert testimony must be based on reliable principles and methods; the trial judge serves as gatekeeper.
Application (model). Dr. X's theory has not been tested, peer-reviewed, or generally accepted in biomechanics. Because Daubert requires the trial judge to assess reliability through factors like testing, peer review, error rate, and general acceptance, the fact that Dr. X's theory fails all four indicia and remains untested means the methodology lacks the minimum indicia of reliability required by Rule 702.
Pick the right element for each blank:
g1.
g2.
g3.
Conclusion. Therefore, the court should exclude Dr. X's testimony.
MBE Check · multiple choice
W, a non-expert eyewitness, testifies, "The car was going about 50 miles per hour." D objects on Rule 701. Admissible?
Practice Drill · tap to build the rule
Drop the chips here in correct order:
Tap chips to add → tap chips in the target to remove: