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Evidence presented in court that is produced from scientific tests or studies.
Scientific evidence is evidence culled from a scientific procedure that helps the trier of fact understand evidence or determine facts at issue in a judicial proceeding. Under rule 702 of the federal rules of evidence and similar state court rules of evidence, "a witness qualified as an expert by knowledge, skill, experience, training, or education" may testify and offer opinions in court if "scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue." Article VII of the Federal Rules of Evidence contains other rules on expert testimony and scientific evidence. All states have rules on expert testimony and scientific evidence that are similar to the rules in article VII.
Expert testimony on scientific evidence is different from ordinary testimony from laypersons. A lay witness may testify to inferences and give opinions only if they are rationally based upon the witness's perceptions of the subject of the testimony. Experts, by contrast, may give opinions and testify about possible inferences based in part on information obtained from secondhand sources and not from observation of the object of the testimony. For example, a layperson would not be allowed to take the witness stand and offer an opinion on a plaintiff's injury unless the individual had witnessed relevant information regarding the injury. However, a doctor who is certified as a specialist in the particular injury could take the stand and offer opinions on the injury based not only on an examination of the plaintiff but also on secondhand information that is normally relied on by experts in that particular field of medical study.
One of the most important issues that arises in expert testimony is which scientific procedures a court should accept as evidence. Many scientific procedures are not seriously in dispute and are accepted by courts with little or no inquisition into their validity. Examples include fingerprint tests for purposes of identification, blood tests, breathalyzer tests for alcohol consumption, and ballistics tests of bullets and their impact areas. These scientific procedures are so widely accepted that a court may take judicial notice of the procedure's validity. Judicial notice means that the parties in the case do not have to present evidence to the court to establish the validity of the scientific procedure. In some instances legislatures have specifically authorized the use of scientific tests, such as breathalyzer tests for suspected drunk drivers.
Whether they are judicially noticed or legislatively mandated, scientific tests that are universally accepted must be presented by a qualified expert. A person is established as a qualified expert before the court through questioning by the attorney who is using the witness as an expert. The attorney asks a series of questions to establish that the witness has adequate education and training to testify as an expert—a process called laying a foundation for the witness. Once the court is convinced that the witness is an expert on the procedure or subject matter that will be presented as evidence, the witness gives an expert opinion to the exact procedures that were used or the factual circumstances that arose in the case at hand. For example, assume that a person sues a doctor for medical malpractice, arguing that the defendant failed to set a broken bone properly. If the plaintiff offers a bone specialist as an expert witness on the issues surrounding the care he received from the defendant, the expert witness must testify about the witness's credentials and give details about the plaintiff's treatment.
Some scientific tests and examinations that are not universally accepted are nevertheless generally considered reliable. Some examples are neutron activation analysis to determine the identity of goods, voiceprints to determine a person's identity, and genetic testing or DNA analysis. These types of scientific procedures may be accepted in the medical communities, but they are not so established that they may be judicially noticed as automatically valid sources of scientific evidence. They may be admitted as evidence, but only after an expert witness has testified to the validity of the test. In determining whether to admit scientific evidence from procedures that are not universally accepted, a court must ask whether the test is reliable. A technique's reliability depends on a number of factors, including whether the technique can be or has been tested, whether it has been subjected to peer review, whether the test procedures have been published, whether the test has a margin of error and, if so, at what rate, and whether the technique, as applied, conformed to existing standards for the test (Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 113 S. Ct. 2786, 125 L. Ed. 2d 469 ).
In Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137, 119 S. Ct. 1167, 143 L. Ed. 2d 238 (1999) the U.S. Supreme Court ruled that the Daubert standards govern not just the admissibility of scientific evidence in federal court, but should be applied to all witnesses seeking federal court approval to testify as an expert. Thus, the Supreme Court found that a purported expert on tire failure was subject to a Daubert inquiry before he could be permitted to testify on the subject in a products liability trial, even if some of his proffered testimony was not wholly "scientific." The lower court had attempted to draw a distinction between scientific expert for which the Daubert standards did apply and a technical expert for which the Daubert standards did not apply. By expanding the daubert test, the Court reemphasized the trial court's broad discretion in matters of expert testimony.
In some instances courts are reluctant to admit certain scientific evidence because the procedures yield results that are not considered sufficiently reliable to be used as evidence. Such procedures include polygraph and chemical tests that have been created to determine whether a person is telling the truth. If all parties agree that testimony derived from such procedures shall be admissible, however, a court is free to allow the evidence to be introduced.
In any case, regardless of the level of acceptance of a particular scientific procedure, the scientific evidence presented must be relevant to the issue at hand. Furthermore, the scientific evidence must have been obtained in a manner that is consistent with the way such evidence is normally obtained. For instance, assume that a physicist intends to testify to the speed of the defendant's vehicle in a personal injury case stemming from a car accident. If the physicist used different methods from those used by other physicists in determining a vehicle's speed, the court may refuse to allow the physicist to testify as to the vehicle's speed.
An expert witness giving testimony on scientific evidence may offer opinions on issues related to that evidence. An expert witness may also give an opinion on the ultimate issue in the case. Under rule 704 of the Federal Rules of Evidence, however, an expert witness testifying with respect to the mental state or condition of a criminal defendant may not state "an opinion or inference as to whether the defendant did or did not have the mental state or condition constituting an element of the crime charged or of a defense thereto." This rule, which is applied by courts only in criminal cases, was approved by the U.S. Congress in 1984, largely in response to the outcome of the criminal prosecution of John Hinckley, who attempted to assassinate President Ronald Reagan in 1981. Hinckley was charged with attempted assassination, assault on a federal officer, and use of a firearm in the commission of a federal offense, but was found not guilty by reason of insanity after the jury heard testimony from a psychiatrist who declared that Hinckley could not be found guilty because he lacked the knowing mental state required for a conviction on the charges.
The weight given to scientific evidence may vary according to the particular test that yielded the evidence. One party's expert testimony may be convincing, but it may not be dispositive of the case because the other party may have experts from the same field who have studied the same evidence and come to different conclusions. Experts have become indispensable to the vast majority of litigated cases, and many cases, civil and criminal alike, come down to a battle between experts. One notable exception to this trend is the paternity case, in which blood test results or DNA test results can establish the ultimate issue in the case. This is true, however, only if the parties in the paternity case agree that the particular tests will be conclusive and if the tests show that the individual named as the father could not be a parent of the child in question. If the tests show that the individual named as the father could be the parent, the test results will not dispose of the case, and the parties will have to present further evidence.
Courts have the discretion to appoint an expert witness to testify to scientific evidence. Under rule 706 of the Federal Rules of Evidence and similar state court rules of evidence, a court may appoint an expert to present evidence on a particular topic and order compensation for the expert's time and effort. Typically, in a civil case, the parties must apportion the costs as the court directs. In just compensation cases under the Fifth Amendment and in criminal cases, the court orders payment for the expert out of government funds.
One of the most well-known experts on scientific evidence in the United States is Barry Scheck, a criminal defense lawyer who rose to prominence during the 1995 O.J. Simpson murder trial as a member of Simpson's so-called "Dream Team." In 1992 he and fellow Dream-Team member Peter Neufeld opened the National Association of Criminal Defense Lawyers' Innocence Project, a nonprofit legal clinic at the Benjamin N. Cardozo School of Law in New York. Through testing of dna evidence, the Innocence Project has helped exonerate 127 wrongly convicted inmates. Scheck, 43, has chronicled the stories of his exonerated clients in books and on the lecture circuit. He also assisted Colorado prosecutors and police officers investigating the Jon-Benet Ramsey murder case.
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