Expert witnesses are persons that have more than usual experience, training or education in an area and can help the jury better understand certain aspects of the case.
There are many different types of experts that may testify in personal injury trials. Sometimes, there are economists that explain the economic impact of the injury and earning potential over a lifetime. There are also vocational experts that discuss the cost and likely result of efforts to retrain a person who has been injured and unable return to his or her job. Very often, there are experts in accident reconstruction that build models or make graphic presentations of the accident to understand it better.
Engineers are sometimes used to explain in scientific terms why elements of accidents may seem to contradict common sense. For example, a bumper to bumper accident even at a slow speed can produce a more serious injury than a higher speed impact with greater property damages. The expert will explain that today’s stgronger and more rigid bumpers act as “force transmitters” and the effect can be like bowling balls colliding and bouncing back causing a more severe injury to a passenger. Other parts of the car are designed to “crumple” upon impact and sometimes a lesser injury can result from a bigger crash.
As the end of the trial, the jury may have heard contradictory expert testimony and must rely on their own common sense and the credibility of each expert.
Indeed, all jury trials are intimately dependent on the common sense of the jury to reach the truth and return a fair verdict given that the testimony of many witnesses, expert and otherwise, often vary in some fashion.
Most of us who do a lot of jury trial work feel that juries almost always get it right in the end.