Who Can Be an Expert Witness?
Rules about expert witnesses are set by state and federal rules of evidence, depending on whether your case is in state or federal court.
According to the Federal Rules of Evidence, a qualified expert witness is someone who has knowledge, skill, education, experience, or training in a specialized field. These qualifications are generally also required of expert witnesses in state courts.
Under federal rules, experts must base their testimony on sufficient facts or data of the type reasonably relied upon by experts in their field, in order to help the jury understand issues that typically require specialized knowledge. While non-expert witnesses can only testify about what they've seen or heard, expert witnesses are generally allowed to give their specialized or professional opinion.
States have similar rules, though there are notable differences among states when it comes to the admissibility of expert testimony.
BASIS AND FUNCTION OF EXPERT WITNESS
The expert witness’ existence is created and perpetuated by the legal system. But for the Rules of Evidence, consulting and testimonial evidence would not exist. A simplified restatement of Federal Rules 701–706 (Figure 1) is that a qualified expert may give his opinion to help the court understand evidence, or to establish a fact in issue. States that have not adopted the Federal Rules of Evidence generally have similar rules or statutes governing expert witness qualifications and testimony. The expert witness performs two primary functions: 1) the scientific function — collecting, testing, and evaluating evidence and forming an opinion as to that evidence; and 2) the forensic function — communicating that opinion and its basis to the judge and jury. A general rule of evidence is that witnesses may only testify to what they have personally observed or encountered through their five senses. VOIR DIRE. FROM THE FRENCH, MEANING ‘TO SPEAK THE TRUTH.’ Qualifying the Expert Witness: A Practical Voir Dire Gil I. Sapir, JD, MSc.
CATEGORIES OF EXPERT WITNESS
An expert may be used in basically two different capacities — consultation or for testimony. Consulting and testimonial witnesses are the basis for expert witnesses. They are derived from five general categories of expertise.
1. Lay people: common sense and life long experience.
2. Technician/examiner: limited and concentrated training, applies known techniques, works in a system and taught with the system [e.g., investigator and supervisors (observers and viewers)]. The technician is generally taught to use complex instruments (gas chromatographer, infrared spectrophometer, mass spectrophotometer) or even “simple” breath alcohol testing equipment as “bench operators,” who have only a superficial understanding of what the instrument really does, and how the readout is generated. “Bench operators,” who qualify as expert witnesses, are not competent to explain the instrumentation used unless it is established that they received the training and education necessary to impart a thorough understanding of the underlying theories.
3. Practitioner: material and information analysis and interpretation.
4. Specialist: devoted to one kind of study or work with individual characteristics. 5. Scientist: conducts original empirical research, then experiments to verify the validity of the theory; designs and creates instrumentation and applied techniques; is published in own field with peers; and advances his field of knowledge.