From Wikipedia, the free encyclopedia

Evidence
Part of the common law series
Types of evidence
Testimony · Documentary evidence
Physical evidence · Digital evidence
Exculpatory evidence · Scientific evidence
Demonstrative evidence · Real evidence
Eyewitness identification · DNA · Lies
Relevance
Burden of proof · Laying a foundation
Subsequent remedial measure
Character evidence · Habit evidence
Similar fact evidence
Authentication
Chain of custody
Judicial notice · Best evidence rule
Self-authenticating document
Ancient document
Witnesses
Competence · Privilege
Direct examination · Cross-examination
Impeachment · Recorded recollection
Expert witness · Dead man statute
Hearsay (and its exceptions)
Hearsay: in U.K. law · in U.S. law
Confessions
Excited utterance · Dying declaration
Party admission · Ancient document
Declarations against interest
Present sense impression · Res gestae
Learned treatise  · Implied assertion
Other areas of the common law
Contract law · Tort law · Property law
Wills and Trusts · Criminal law

This article is about the legal concept. For scientific evidence in pure science, see Scientific evidence.

Contents 1 History 2 Educating witness 2.1 Role 2.2 Frye test 2.3 Daubert test 3 Reporting witness 4 Interpreting witness 5 Further reading

The educating witness teaches fact-finder (jury or, in a bench trial, judge) about the underlying scientific theory and instrument implementing theory. This witness is an expert witness, called to elicit opinions that a theory is valid and the instruments involved are reliable. The witness must be accredited as an expert witness, which may require academic qualifications or specific training.

• Judicial Notice: may moot the need for this witness.
• Qualifications: Relative experience based on complexity and subtlety of the subject-matter. This witness is on high plane of abstraction about the validity and reliability.
• Validity of Theory: Most jurisdictions require the theory used by an expert witness to meet certain qualifications before being used in court. The two most common are the Daubert and Frye tests.

The Frye test, coming from the case Frye v. United States (1923), said that admissible scientific evidence must be a result of a theory that had "general acceptance" in scientific community. This test results in uniform decisions regarding admissibility. In particular, the judges in Frye ruled that:

Just when a scientific principle or discovery crosses the line between experimental and demonstrable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized, and while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs.

This test has been criticized as misunderstanding the scientific process and being based on the assumption that a jury is unable to evaluate scientific testimony. The goals of the test were to avoid evidence from overly questionable or controversial scientific theories to be used; it was used to exclude lie-detector results employed by the defense in the original case.

The Daubert test arose out of the United States Supreme Court case Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993). It requires four things to be shown:

• (1) Whether theory will help fact-finder (That is, whether the theory has or can be tested)
• (2) Whether theory has been peer reviewed (This is a component of good science and will improve likelihood the flaws will be found.)
• (3) Whether the theory has a significant rate of error
• (4) Whether the theory is "generally accepted" (not required but it helps to know scientific community approves.)

The Federal Rules of Evidence use the Daubert Test. See FRE 702.

Reporting witness: Called after teaching witness leaves stand. Usually the laboratory technician who personally conducted the test. Witness will describe both the test and the results. When describing test, will venture opinions that proper test procedures were used and that equipment was in good working order.

• Whether witness is qualified to conduct test. Could qualify as expert by virtue of "skill" gained through "experience & training" (FRE 702)—usually experiential, on-the-job training.
• Whether witness received the correct object to be tested. (Chain of Custody satisfying FRE 104(b)).
• Whether instrument(s) involved were in proper working order.
• Proof test procedures were used. This split the courts, but under CL, most Jx require foundational proof that the witness used proper test procedures on the occasion in question.
• Statement of Test Result: witness says what the results were. Excellent place to put physical evidence. Remember, validating scientific evidence raises a logical relevance issue, as does the authentication (e.g. with enlarged photo).

Interpreting (Evaluating) Witness: Sometimes not needed 1) when test result is self-explanatory or pass-fail, or 2) when there is a statutory presumption obviating the need (e.g. drunk driving statutes and a test showing raised blood alcohol levels). Otherwise, this witness needed to complete the foundation. Syllogistic in nature: 1) states the interpretive standard (Rule or Major Premise), applies the standard to the test result (minor premise) and derives a conclusion.

• Qualifications: a hybrid with both academic and experiential qualifications.
• Will base finding on the Reporting witness. [Experts may base opinion on 1) what personally observed, 2) facts that are the type of data customarily considered by practitioners of the specially and 3) hypothetically assumed facts.] Ideal if present when Reporter conducted test, but may be permitted in some jurisdictions.
• Some jurisdictions won't accept opinion unless it is a "reasonable scientific opinion." Otherwise, need to consider if the witness can couch the opinion in terms of statistical probably.

For example, in the casebook case of People v. Collins, 438 P.2d 33 (Cal. 1968), an elderly lady was knocked down and robbed by a blond who escaped in yellow car with bearded black man. Defendants met that rough description but could not be conclusively identified. Prosecutor used a mathematics professor to discuss the probability that this couple could be the guilty party. Lower court overruled Defendants' objection. Court held that 1) there was no foundational establishment of the underlying probabilities and 2) the fact that the Defendants' fit a probability model was irrelevant because it doesn't prove they did it.

• Sheila Jasanoff, Science at the Bar: Law, Science, and Technology in America (Cambridge, Mass.: Harvard University Press, 1997).