Civil and criminal trials depend on live witnesses to present testimony. Even when the information being presented is in the form of documents, there must usually be a human witness to authenticate the documents. Witness’s testimony can be divided into factual testimony about matters the witness has personal knowledge of and expert testimony, in which an expert testifies as to conclusions he or she draws from the records in the case. Most of the controversy about witness testimony concerns expert witness testimony. Whereas anyone can be a witness to the facts they personally know, any testimony that requires either an opinion about the meaning of the facts that is based on a scientific analysis, or otherwise requires special knowledge not possessed by the average juror, must be presented by an expert. For example, in a dispute over the sale of land there may be testimony by an appraiser as to the value of the land. Personal injury cases will need an expert to testify about the seriousness of the patient’s injuries and prognosis. In medical malpractice litigation, the plaintiff must present the testimony of an expert who believes that the defendant did not care for the plaintiff properly and that this breach of professional conduct caused the plaintiff an injury. A fraud case may require an expert on accounting standards. A products liability claim against a drug company may require an expert to testify as to whether the drug actually causes the type of injury that is alleged.