Editing Expert witness (section)

==Role==
Expert witnesses are called upon in the court system to serve as an objective party to the lawsuit and never function as an advocate for one side or the other. Expert witnesses are present in litigation to explain complicated scientific issues, not to influence the jury or judge with fervor. The main responsibilities of expert witnesses are to evaluate potential problems, defects, deficiencies, or errors only when able to fully appreciate a process or system.<ref name=":1">Cohen, Kenneth (2015-08-05). ''Expert Witnessing and Scientific Testimony : A Guidebook, Second Edition''. Chapman and Hall/CRC. {{ISBN|9781498721097}}.</ref> Expert witnesses are obligated to study the processes prior to making a survey or postpone the assignment prior to potentially missing the target due to lack of specific condition understanding. They are called to testify under the assumption that all the preparation required for a competent evaluation of the process has been made.

Typically, [[expert]]s are relied on for opinions on severity of [[injury]], degree of [[sanity]], cause of failure in a machine or other device, [[Wrongful dismissal in the United Kingdom|loss of earnings and associated benefits]], care costs, and the like. In an [[intellectual property]] case an expert may be shown two music scores, book texts, or circuit boards and asked to ascertain their degree of similarity. In the majority of cases, the expert's personal relation to the defendant is considered and usually adjudged to be irrelevant.

The [[tribunal]] itself, or the [[judge]], can in some systems call upon experts to technically evaluate a certain [[fact]] or [[Philosophy of action|action]], in order to provide the court with a complete knowledge on the fact/action it is judging. The expertise has the legal value of an acquisition of data. The results of these experts are then compared to those by the experts of the parties.

The expert has a great responsibility, and especially in [[Penal law|penal trials]], and [[perjury]] by an expert is a severely punished [[crime]] in most countries. The use of expert witnesses is sometimes criticized in the [[United States]] because in [[Civil law (common law)|civil trials]], they are often used by both sides to advocate differing positions, and it is left up to a [[jury]] to decide which expert witness to believe. Although experts are legally prohibited from expressing their opinion of submitted evidence until after they are hired, sometimes a party can surmise beforehand, because of reputation or prior cases, that the testimony will be favorable regardless of any basis in the submitted data; such experts are commonly disparaged as "hired guns."<ref>Snow, J.N., & Weed, R. (1997). Mental health forensic issues in Georgia: The role of the expert witness. Georgia Journal of Professional Counselors, 53-65.</ref><ref>Snow, J.N. & Weed, R. (1996). Forensic issues in mental health: The role of the expert witness. Journal of Legal Nurse Consulting, 7(4), 2-13.</ref>

=== Qualifications ===
An expert witness at the time of trial is qualified by the court and must be re-qualified each time that person comes to trial for the offering of opinions. The qualification is given by each trial judge and takes place regardless of prior appearances by a particular expert witness. Expert witnesses are those whom the court has deemed qualified to speak on a topic to provide background to anyone on a lay jury.<ref>"Forensic Ethics and the Expert Witness". 2007. {{doi|10.1007/978-0-387-35383-8}}.</ref>

===Duties in United States courts===
In high stakes cases multiple experts, in multiple topics, are often retained by each party. Although it is still relatively rare, the court itself may also retain its own independent expert. In all cases, fees paid to an expert may not be contingent on the outcome of the case.

Expert evidence is often the most important component of many civil and criminal cases today. [[Fingerprint]] examination, [[blood analysis]], [[DNA fingerprinting]], and [[forensic firearm examination]] are common kinds of expert evidence heard in serious criminal cases. In civil cases, the work of [[accident analysis]], [[Forensic engineering#Forensic engineering|forensic engineers]], and [[Forensic accounting|forensic accountants]] is usually important, the latter to assess [[damages]] and [[Costs (law)|costs]] in long and complex cases. [[Intellectual property]] and [[medical negligence]] cases are typical examples.

Electronic evidence has also entered the courtroom as critical forensic evidence. Audio and video evidence must be authenticated by both parties in any litigation by a forensic expert who is also an expert witness who assists the court in understanding details about that electronic evidence.

[[Voice-mail]] recordings and closed-circuit television systems produce electronic evidence often used in litigation, more so today than in the past. Video recordings of bank robberies and audio recordings of life threats are presented in court rooms by electronic expert witnesses.

=== Rules of evidence and code of procedure ===

==== Hearsay rule ====
One important rule that applies to the expert witness but not the percipient witness is the exception to the hearsay rule. A percipient witness tells only what he/she actually knows about a case and nothing more. Percipient witnesses cannot give opinions nor conjecture regarding a hypothetical set of conditions.<ref name=":1" /> Conversely, the court does allow an expert to testify about issues that may not be personally known by them. This allows the expert to rely upon scientific articles, discussions with colleagues on the subject, testimony read in preparation for testimony in the case and similar pieces of information not personally known to the expert.

==== Chain of custody ====
{{main|Chain of custody}}
It is important that expert witnesses who handle evidence maintain a proper [[chain of custody]] such that they are able to authenticate the evidence, prove that it is what they represent it to be, when testifying at trial. Most notably in the context of a criminal prosecution, an expert witness who evaluates or examines an item pertinent to an investigation or case evaluation may add an entry to a "chain of custody" document,<ref name=":1" /> a form that contains the item's description, the time and date of release for all prior custodians of the item, and the time and date of release to the witness.

==== Weight of testimony ====
In the case of an expert witness, the weight of his/her evidence depends heavily on the foundation support established prior to an opinion being given. Examples include educational background, review of scholarly works, field studies and trainings which all lead up to developing a foundation of knowledge for credibility of a testimony. Before trial, all experts must prepare a report summarizing their analysis and conclusions and share the report with all other parties.<ref name=":1" /> This allows other parties to effectively cross-examine the expert.