Expert Witness Testimony in Legal Proceedings

Expert Witnesses

Professor Caroline Cinquanto

Professor Jeanine Linehan



Opinion Testimony by Lay Witnesses only if



(a)  rationally based on witnesses perception;



(b)  helpful to understand the witness’s testimony or

determine a fact in issue;  

and



(c)  not based on scientific, technical, or other specialized

knowledge within the scope of Rule 702.



A witness who is qualified as an expert by knowledge, skill,

experience, training, or education may testify in the form of

an opinion or otherwise if:



(a)  

helpful

 to the trier of fact;



(b) based on 

sufficient

 facts and data;



(c) 

reliable

 principles and methods; and



(d) apply principles and methods 

reliably

.

An expert must have greater knowledge that a lay person.  Once the

expert is shown to have some expertise, the issue is then one of

credibility.

(e.g. carpenter, 1980s hacker, recent med grad)



Used to be 

Frye

 – scientific tests and principles only

admissible if those tests and principles have gained general

acceptance in the particular field in which it belongs.



Now – 

Daubert

 – Key inquiry now is whether the evidence is

relevant and reliable.  Question:  whether eh resonating or

methodology underlying the testimony underlying the

testimony is scientifically valid and whether that reasoning or

methodology can be applied to the facts in issue.



1. Can it be tested?



2.  Subject to peer review?



3.

Known rate of error?



4.  Generally accepted?



Judge is the Gatekeeper and will hold a Daubert Hearing



Yes – impression testimony, cell tower evidence, DNA,

fingerprint, breathalyzer



No – Cancer studies in mice and humans; tire failure analyst



Rule 703 states that an expert may base his opinion on facts and

data not in evidence so long the facts and data are the type such

experts reasonably use in their field.  Furthermore, the facts and

data need not be admissible for the opinion to be admitted.  But

if inadmissible, proponent can only disclose if the probative

values outweighs the prejudicial impact.  Opponent can always

elicit facts (inadmissible or no) on cross. Why?  To test the

credibility of the opinion.



E.g.  Expert based on lab reports, depositions and x-rays even if

not admitted into evidence.



An expert can testify without first testifying to the underlying

facts or data.  On cross, an expert can be required to

disclose.



Why can this be helpful?



Opinion as to the Ultimate Issue



(a) In general:  ok



(b) Exception:  in a criminal case, cannot state if the

defendant did or did not have a mental state or condition

that constitutes an element of the crime charged or of a

defense.



Introduction



Name



Employment



Are you here today to render an opinion about XXXX?



Before we get to that opinion, I would like to talk about why

your qualified to give that opinion.



Background



Education



Work History



Published



Awards



Honors



Your Honor, we tender the witness in the (area in which he is

qualified – BE SPECIFIC)



Objection?



Voir Dire



Stipulate?



You stated earlier you were prepared to render an opinion

about XXXXX.  Before we get to that, please tell us what

things you relied upon to come to your opinion.



Will your opinion be to a reasonable degree of XXXXX

certainty?



Ask for the Opinion



Exhibits and visual aids



Role of the teacher



Simple language



Organized



Qualifications



Bias/Interest



Data Relied On



Assumptions



Prior Inconsistent Statements



Treatises



Experts Disagree