Expert and Non-Expert Opinions in Court

One of the less-explored aspects of the George Zimmerman trial in Florida was the judge’s decision that experts could not testify as to whose voice was heard screaming on the 911 recording, but that relatives of both Zimmerman and Trayvon Martin could. These rulings were an application of the rules of evidence regarding opinion testimony, which differs somewhat for experts and non-experts. Oddly enough, the trial began only a few weeks before a change in Florida law that might have led to a different ruling on whether the experts could testify.


The first requirement for an expert to testify is to actually demonstrate that he or she is an expert. This can be shown by education and training, knowledge, skill, or experience. If you have seen My Cousin Vinny, you may remember the scene in which Marisa Tomei’s character is offered as an expert on automotive knowledge. That was a good depiction of how a dispute over an expert’s basic qualification is resolved.

The second requirement is that the expert’s testimony be of assistance to the judge or jury in understanding the evidence or deciding something in dispute. Different courts use one of two different standards in deciding this question, and usually a special hearing is held if there is a dispute. In the federal courts and Oregon, the standard is whether the expert bases his or her opinion on accurate information, using sufficiently reliable scientific methods or principles, and applies those principles to the data. Washington uses an older standard, that the science is generally accepted. This can be more restrictive than the federal and Oregon rule, in that newly emerging concepts may take longer to accept.

Florida has just changed its standard. It has long used the general acceptance standard, but shortly before the Zimmerman trial, the legislature passed an amendment to the expert testimony rule switching to the reliability test. This change came into effect on July 1, after the trial started, so the judge ruled using the general acceptance standard.

In the Zimmerman case, the question was whether it was possible for an expert to identify the screams. At the pretrial hearing, the defense had experts testify that it was not possible to identify screams and that one second of speech, recorded over a telephone, was not enough to identify. The defense experts also said that the methods used by prosecution experts were not generally accepted. The judge agreed with the defense experts. It is possible that if the hearing was held only a few weeks later, under the reliability standard, the result might have been different, but the defense experts probably would have said that the methods were not reliable.


Non-experts are permitted to testify to opinions in a narrower and more general range of situations than experts. The witness has to base the opinion on his or her own perceptions, and the opinion has to help lead to a clear understanding of the witness’ other testimony or deciding a matter in dispute. Among the common subjects for non-expert opinions are identifications of handwriting and voices by a witness familiar with the subject. It is not surprising that in the absence of expert witnesses, relatives of both Zimmerman and Martin were asked to identify the voice on the 911 recording.

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Whether to use an expert or non-expert opinion in a case is often a decision that a lawyer has to discuss with a client. Sometimes, it is necessary to bring in an expert to prove a necessary point. For example, in accident cases, whether a particular injury was caused by the accident may need to be shown. Other times, using an expert may be more of a tactical question. For example, if the witnesses to a will cannot be located, and they never signed an affidavit to confirm the will, identification of the signature by either an expert or a non-expert can be used. If someone familiar with the testator’s signature can be found, that would be less expensive than hiring an expert. In general, if your lawyer identifies the possible need for an opinion, they may discuss with you whether an expert would be necessary or desirable, and whether an opinion by a non-expert might be used instead.

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