In the immortal words of Bob Dylan, "You don't need a weatherman to know which way the wind blows." Yet, in legal battles, some types of knowledge do require experts to explain certain matters to a judge or jury. An expert is allowed to give very different opinion testimony than your average witness and usually gets paid a lot more.
Qualifying an Expert
If an issue in a lawsuit is sufficiently complex that an ordinary person might have trouble understanding it, the court can permit expert testimony. An expert is someone with specialized training, education or experience in a field. Advanced degrees are not required. The qualifications for an expert depend on the area at issue. To use the oft-repeated formulation, if you want an expert to tell you how bees fly, hire an aeronautical engineer; if you want an expert to tell you whether bees always take off into the wind, hire a beekeeper. When an attorney wants to use an expert, he must establish to the judge's satisfaction that the person is knowledgeable and competent in the field by reviewing her credentials. The other party's attorney may also question her before the judge rules.
Lay Witness Opinion Testimony
Generally, only people who observed something about the facts of a case can be called as lay, or non-expert, witnesses and testify only about their personal knowledge. This is the rule in federal court and has been adapted by most states as well. Witnesses must testify about what they know, not what they speculate to be true or what they heard from a friend or neighbor. For example, if James Jones saw someone accused of drug dealing handing out baggies of white powder, he could only testify about the hand-off. He could not testify that, in his opinion, the powder was probably heroin, even if that was the rumor in the neighborhood.
Expert Opinion Testimony
An expert, on the other hand, can offer opinion testimony as long as the subject is within her specialized field of knowledge. She doesn't need to limit her opinions to matters she personally observed or experienced. Rather, an expert bases her opinion on other witness testimony or written reports, or anything an expert in her field might usually use as the basis of an opinion. The other party's attorney can ask the expert about the matters on which she based her opinion and, if they appear weak or biased, argue the expert testimony should not be given much weight.
Money Often Buys Expert Witnesses
If an eyewitness to an accident conditioned her testimony on being paid a large sum of money, she would herself be committing a crime. People with personal knowledge of a matter are obliged to testify when subpoenaed, and do so for free. Expert witnesses can and do charge for their services, often a high hourly fee. They charge not just for testifying, but also for preparing for trial, traveling and waiting. You cannot bring some cases, like medical malpractice, without hiring an expert to opine that the doctor defendant did not meet the standards of the profession. It is so lucrative to be an expert witness that some professionals give up their day jobs and become professional witnesses, but a good attorney on the other side can use this to undercut the impact of their testimony.
- Free Legal Dictionary: Expert Testimony
- Official California Legislative Information: Evidence Code, Section 800 - 805
- Nolo: Expert Witness Testimony
- Nolo: Witnesses and Personal Knowledge
- Boulder County Bar Association: Bar Media Manual, Opinions and Expert Testimony
- University of Rhode Island, Department of Chemistry: Qualifying the Expert Witness - A Practical Voir Dire
- Photo Credit Sean Gallup/Getty Images News/Getty Images
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