The topic of expert witnesses and the scientific and technical evidence they bring into the trial, is a complicated one. In many law schools, this topic is the subject of an entire 2-hour advanced evidence class. There are whole casebooks devoted to this subject alone, and the leading reference book (Faigman, Kaye, Saks & Sanders) is 4 volumes. We will give it only cursory coverage here. There is not time to do more in an introductory evidence class.

Rule 702 governs expert testimony. Analyzing the admissibility of expert testimony consists of several stages:

(1) Is there an appropriate issue? Rule 702 says that experts may testify only "If specialized knowledge will assist the jury." This is the equivalent of the "helpfulness" foundation for lay witness opinions.

(2) The person put forward as an expert must have educational qualifications and professional experience in an appropriate area of expertise. Rule 702 says that the witness must be "qualified as an expert."

(3) The expert must base his or her opinion on information, observations, tests, experiments, and other data. This is equivalent to the personal knowledge rule for lay opinions. Opinions must be based on enough data to make them reliable. However, experts do not need personal knowledge. They may review files and records and offer opinions as consultants.

(4) The expert's opinion must be rational. It must be:
a) Within the expert's area of expertise and related to the issue.
b) Rationally related to data
c) Scientifically reliable.

Note on "scientific reliability," also known as the "Daubert" test (from Daubert v. Merrell-Dow, a Supreme Court case):

Opinions based on scientific knowledge will be more helpful to jury that opinions based on advertising, quackery, abstract philosophy, or outright fraud. The courts are therefore faced with a difficult task -- they must distinguish "true" scientific knowledge from "false" science. Who has to make this decision? A panel of experts from the national science foundation? The dean of the college of arts & sciences at IU? A high school science teacher? No. The decision must be made by a judge who was probably a business & finance major as an undergrad, and then went to law school and has never taken a science course in his or her life after high school biology (which was devoted entirely to dissecting frogs because school officials were afraid to anger fundamentalist Christians who objected to 90% of the rest of the science curriculum).

The Supreme Court tried to help these poor judges in the Daubert case (and in amendming Rule 702 -- see p. 473) by giving them suggestions on what to look for: To be reliable, matters of science must:

A) Be derived from scientific methodology -- that is, theoriesy tested by neutral scientists through controlled studies.

B) Be subjected to peer review and publication -- no "private" or proprietary data;

C) Have a small rate of error in results (no statistical significance of results unless p<.05.

D) Have achieved widespread acceptance if it has been around for awhile (Among educated elite -- not among general public -- e.g., evolution).

Example #1 (expert witness from "My Cousin Vinny")

Gambini: Your Honor, the defense calls as its first witness Miss Mona Lisa Vito.

Prosecution: I object your Honor, this person 's not on the witness list.

G: This witness is an expert in the field of automobiles, and is being called to rebut the testimony of George Wilbur.

Judge: Officer?

G: Would you please instruct the officer to escort Miss Vito to the witness stand please?

Bailiff: Hold up your right hand. Do you swear to tell the truth, the whole truth and nothing but the truth so help you god?

Vito: Yeah.

G: Miss Vito, you're supposed to be some kind of expert in automobiles, is that correct? Is that correct?

J: Will you please answer the counsellor's question?

V: No, I hate him.

G: May I have permission to treat Miss Vito as a hostile witness?

V: You think I'm hostile now, wait till you see me tonight.

J: Do you two know each other?

G: Yeah, she's my fiancé.

J: Well, that would certainly explain the hostility.

Trotter: Your Honor, I object to this witness. Improper foundation. I'm not aware of this person's qualifications. I'd like to voir dire this witness as to the extent of her expertise

J: Granted. Mr. Trotter, you may proceed.

T: Miss Vito, what's your current profession?

V: I'm an out of work hairdresser.

T: Out of work hairdresser? Now, in what way does that qualify you as an expert in automobiles?

V: It doesn't.

T: In what way are you qualified?

V: Well, my father was a mechanic, his father was a mechanic, my mother's father was a mechanic, my three brothers are mechanics, four uncles on my father's side are mechanics--

T: Your family is obviously qualified, but have you ever worked as a mechanic?

V: Yeah, in my father's garage, yeah.

T: As a mechanic? What did you do in your father's garage?

V: Tune-ups, oil changes, brake relining, engine rebuilds, rebuild some trannies, rear end--

T: Okay, okay. But does being an ex-mechanic necessarily qualify you as being an expert on tire marks?

V: No, thank you, goodbye.

Judge: Sit down and stay there until you're told to leave.

G: Your Honor, Miss Vito's expertise is in general automotive knowledge. It is in this area which her testimony will be applicable. Now, if Mr. Trotter wishes to voir dire the witness, I'm sure he's going to be more than satisified.

J: Okay.

T: All right, all right. Now, Miss Vito, being an expert on general automotive knowledge, can you tell me what would the correct ignition timing be on a 1955 Bel-Air Chevrolet with a 327 cubic inch engine and a four-barrel carburetor?

V: It's a bullshit question.

T: Does that mean that you can't answer it?

V: It's a bullshit question, it's impossible to answer.

T: Impossible because you don't have the answer.

V: Nobody could answer that question

T: Your honor, I move to disqualify Miss Vito as an expert witness.

J: Can you answer the question?

V: No, it is a trick question

J: Why is it a trick question

V: Cause Chevy didn't make a 327 in '55. The 327 didn't come out till '62, and it wasn't offered in a Bel-Air with a four-barrel carb 'til '64. However, in 1964 the correct ignition timing would be four degrees before top dead center.


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