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what is scientific evidence
What Is Scientific Evidence?

Scientific evidence is most often presented in court by an expert witness testifying on expert opinions. It also includes expert testimony that goes beyond science. The scientific expert is frequently called upon to interpret results and draw conclusions about what results mean in the case being tried.

functions of the forensic scientist
Functions of the Forensic Scientist

Forensic Scientists rely primarily on scientific knowledge. However, only half the job is performed in the laboratory while the other half takes place in the courtroom.

These functions fit into three categories:

1 analyzing of physical eviden ce

1. Analyzing of Physical Evidence





2 providing expert testimony
2. Providing Expert Testimony

Forensic Scientist are called on to evaluate evidence when the court lacks the expertise to do so

Must establish competency by citing educational degrees, number of years of occupational experience membership in professional societies, special courses taken and any professional articles or books published.

Cross-examination may reveal weaknesses in background and knowledge

Demeanor and ability to explain scientific data clearly and logically to a judge and jury of non-scientists

Must be an advocate of truth and not take a side

3 providing training
3. Providing Training

Evidence must be properly recognized, collected and preserved if it is to have value.

Many, but not all crime laboratories keep trained “evidence technicians”.

Sometimes a patrol officer or detective collects the evidence.

All officers engaged in fieldwork must be familiar with evidence collection.

These people are trained by laboratory staff through extensive personal contact, lectures, laboratory tours and/or dissemination of manuals.

admissibility of scientific evidence
Admissibility of Scientific Evidence

How does the court decide whether or not to accept scientific evidence? The judge and jury are typically not scientifically trained.

Several court cases illustrate the steps in the development of admissibility.

frye vs united states 1923
Frye vs. United States (1923)

Scientific validity of polygraph is rejected

Court ruled that in order to be admitted as evidence in trial the questioned procedure, technique or procedure must be “generally accepted” by a meaningful segment of the scientific community.

Collection of experts called in to testify about the validity of scientific issues

Books and papers written on subject reviewed and discussed.

federal rules of evidence 1975
Federal Rules of Evidence (1975):

A code of evidence law governing the admissibility of evidence in the U.S. federal court system enacted in 1975.

Rule 702 applies to scientific, technical or otherwise specialized knowledge.

Individual states are free to adopt different evidence rules but most have codes that are based on FRYE.

courts traditionally use one of these rules for the admissibility of scientific evidence
Courts traditionally use one of these rules for the admissibility of scientific evidence:
  • The Frye Test
    • Frye v. United States (1928) 293 F. 1013
  • The Frye Test Plus or KELLY-Frye test
    • People v. Kelly (1976) 17 Cal.3d 24
  • Daubert Test
    • Daubert v. Merrell-Dow Pharmaceuticals, Inc. 509 U.S. 579, 113 S.Ct. 2786 (1993).
frye standard frye v u s 293 f 1013 d c cir 1923
Frye Standard, Frye v. U.S. 293 F. 1013 (D.C. Cir. 1923)
  • Essentially, for the results of a scientific technique to be admissible, the technique must be sufficiently established to have gained general acceptance in its particular field.
  • This is referred to as the "general acceptance" test by the scientific community.
illinois rules of evidence rule 702 testimony by experts
Illinois Rules of Evidence Rule 702 TESTIMONY BY EXPERTS
  • If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise.

Where an expert witness testifies to an opinion based on a new or novel scientific methodology or principle, the proponent of the opinion has the burden of showing the methodology or scientific principle on which the opinion is based is sufficiently established to have gained general acceptance in the particular field in which it belongs.


Although there had been considerable clamoring for Illinois to adopt the Dauberttest, as the Federal courts and many other jurisdictions have done, the Illinois Supreme Court has made it clear that it is Frye and not Daubertthat must be followed.


the testimony is based upon sufficient facts or data, the testimony is the product of reliable principles and methods, and the witness has applied the principles and methods reliably to the facts of the case.


The Frye test as set forth in Frye v. United States, 293 F. 1013 (D.C. Cir. 1923), is a specific test of admissibility related to expert testimony concerning scientific evidence. Where opinion testimony is based on the expert’s personal knowledge and practical experience, but not based on “studies and tests,” it is not subject to a Frye test. Donnellan v. First Student, Inc., 383 Ill. App. 3d 1040, 1061, 891 N.E.2d 463 (1st Dist. 2008). The Frye test is also known as the “general acceptance” test, as it requires that “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.

the daubert test
The Daubert Test
  • The court suggested the trial court consider various factors to assess scientific validity
  • Has the theory been tested?
  • Has it been subjected to peer review by other scientists?
  • What is the theory’s or technique’s known or potential rate of error?
  • Do standards controlling the application of the theory or technique?
  • Is the theory or technique generally accepted?
daubert v dow pharmaceuticals inc 1993
Daubert v. Dow Pharmaceuticals, Inc. (1993)

“general acceptance” or Frye standard no longer absolute prerequisite.

Trial judge given the task of ensuring an expert testimony rests on a reliable foundation, is relevant to case, and is not repetitive, inflammatory or unnecessarily confusing. (gatekeeper)

daubert ruling suggested areas of inquiry
Daubert Ruling suggested areas of inquiry:

Whether the scientific technique or theory can be (and has been) tested.

Whether the technique or theory has been subject to peer review & publication

The technique’s potential rate of error

The existence and maintenance of standards

Whether the scientific theory or method has attracted widespread acceptance within a relevant scientific community

daubert v merrell dow 1993
Daubert v. Merrell Dow (1993)
  • The Court “REJECTED” the more basic Frye test of “general acceptance” in the scientific community.
  • Daubert requires an independent judicial assessment of reliability .
  • This test requires special pretrial hearings for scientific evidence and special procedures on discovery. 
  • This is a more stringent test that requires knowledge of Type I and Type II error rates, as well as validity and reliability coefficients.
daubert test requires federal judges to ascertain the following
Daubert test requires (federal) judges to ascertain the following:
  • (1) Whether the theory or technique is capable of being or has been tested;
  • (2) Whether it has been subjected to peer review and publication;
  • (3) The known or potential rate of error in using a particular scientific technique and the standards controlling the technique's operation; and
  • (4) Whether the theory or technique is generally accepted in the particular scientific field.
concerns about the daubert ruling
Concerns about the Daubert Ruling:
  • Abandoning Frye’s general acceptance test will result in the introduction of absurd pseudoscientific claims in court
  • Supreme Court rejected these concerns:
    • The judicial system is capable
    • Through vigorous cross-examination, presentation of contrary evidence and careful instruction on the burden of proof are the traditional & appropriate means of attacking shaky but admissible evidence.

Different methods-same results: “Frye in drag”