The expert witness is very important to a case, for the expert witness provides the evidence that is needed in order to prove that a standard of care is relevant. Now, you may not know that there is a difference between a regular witness and an expert witness. A regular witness's testimony can only be of facts surrounding the topic of the case that is being supplied. As for an expert witness, there testimony can be of the facts of all applicable standards and interpret whether or not it is suitable for evidence. They may also supply an opinion of the case. What is stated in a testimony varies from state to state, and therefore may be dismissed a case in some state courts. Many people believe that using expert witnesses during pretrial reviews, because the testimony of an expert witness defeats the point of even having a expert witness.