Expert witness
Encyclopedia
An expert witness, professional witness or judicial expert is a witness
, who by virtue of education
, training
, skill
, or experience
, is believed to have expertise and specialised knowledge
in a particular subject beyond that of the average person, sufficient that others may officially and legally rely upon the witness's specialized (scientific
, technical or other) opinion about an evidence
or fact
issue within the scope of his expertise, referred to as the expert opinion, as an assistance to the fact-finder. Expert witnesses may also deliver expert evidence about facts from the domain of their expertise. At times, their testimony may be rebutted with a learned treatise
, sometimes to the detriment of their reputations.
In Scots Law, Davie v Magistrates of Edinburgh (1953) provides authority that where a witness has particular knowledge or skills in an area being examined by the court, and has been called to court in order to elaborate on that area for the benefit of the court, that witness may give evidence of his opinion on that area.
, degree of insanity
, cause of failure in a machine or other device, loss of earnings, 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 irrelevant.
The tribunal
itself, or the judge
, can in some systems call upon experts to technically evaluate a certain fact
or 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 heavy responsibility, especially in 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 trials
, they are often used by both sides to advocate differing positions, and it is left up to a jury
of laymen 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."
, under the Civil Procedure Rules 1998
(CPR), an expert witness is required to be independent and address his or her expert report
to the court. A witness may be jointly instructed by both sides if the parties agree to this, especially in cases where the liability is relatively small.
Under the CPR, expert witnesses are usually instructed to produce a joint statement detailing points of agreement and disagreement to assist the court or tribunal. The meeting is held quite independently of instructing lawyers, and often assists in resolution of a case, especially if the experts review and modify their opinions. When this happens, substantial trial costs can be saved when the parties to a dispute agree to a settlement. In most systems, the trial
(or the procedure) can be suspended in order to allow the experts to study the case and produce their results. More frequently, meetings of experts occur before trial.
Experts charge a professional fee which is paid by the party commissioning the report (both parties for joint instructions) although the report is addressed to the court. The fee must not be contingent on the outcome of the case. Expert witnesses may be subpoenaed (issued with a witness summons), although this is normally a formality to avoid court date clashes.
harbour in Norfolk
accepted evidence from a leading civil engineer
, John Smeaton
. This decision by the court to accept Smeaton's evidence is widely cited as the root of modern rules on expert evidence. However, it was still such an unusual feature in court that in 1957 in the Old Bailey
, Lord Justice Patrick Devlin
could describe the case of suspected serial killer
Dr John Bodkin Adams
thus: "It is a most curious situation, perhaps unique in these courts, that the act of murder has to be proved by expert evidence."
On the other hand, expert evidence is often the most important component of many civil and criminal cases today. Fingerprint
examination, blood analysis and DNA fingerprinting are common kinds of expert evidence heard in serious criminal cases. In civil cases, the work of accident analysis
, forensic engineers, and forensic accountants is usually important, the latter to assess damages
and 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.
. If the expert finds something that is against its client, the opposite party will not know it. This privilege is similar to the work product
protected by the attorney/client privilege. The non-testifying expert can be present at trial or hearing to aid the attorney in asking questions of other expert witnesses.
An expert testifying in court must satisfy the requirements of Fed. R. Evid. 702. Generally, under Rule 702, an expert is a person with “scientific, technical, or other specialized knowledge" who can "assist the trier of fact,” which is typically a jury. A qualified expert may testify “in the form of an opinion or otherwise” so long as: “(1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case.”
Although experts can testify in any case in which their expertise is relevant, criminal cases are more likely to use forensic scientists or forensic psychologists
, whereas civil cases, such as personal injury, may use forensic engineers, forensic accountants, employment consultant
s or care
experts. Senior physician
s – UK, Ireland, and Commonwealth consultant
s, U.S. attending physician
s – are frequently used in both the civil and criminal courts.
The Federal Court of Australia has issued guidelines for experts appearing in Australian courts. This covers the format of the expert's written testimony as well as their behaviour in court. Similar procedures apply in non-court forums, such as the Australian Human Rights and Equal Opportunity Commission.
Witness
A witness is someone who has firsthand knowledge about an event, or in the criminal justice systems usually a crime, through his or her senses and can help certify important considerations about the crime or event. A witness who has seen the event first hand is known as an eyewitness...
, who by virtue of education
Education
Education in its broadest, general sense is the means through which the aims and habits of a group of people lives on from one generation to the next. Generally, it occurs through any experience that has a formative effect on the way one thinks, feels, or acts...
, training
Training
The term training refers to the acquisition of knowledge, skills, and competencies as a result of the teaching of vocational or practical skills and knowledge that relate to specific useful competencies. It forms the core of apprenticeships and provides the backbone of content at institutes of...
, skill
Skill
A skill is the learned capacity to carry out pre-determined results often with the minimum outlay of time, energy, or both. Skills can often be divided into domain-general and domain-specific skills...
, or experience
Experience
Experience as a general concept comprises knowledge of or skill in or observation of some thing or some event gained through involvement in or exposure to that thing or event....
, is believed to have expertise and specialised knowledge
Knowledge
Knowledge is a familiarity with someone or something unknown, which can include information, facts, descriptions, or skills acquired through experience or education. It can refer to the theoretical or practical understanding of a subject...
in a particular subject beyond that of the average person, sufficient that others may officially and legally rely upon the witness's specialized (scientific
Scientific evidence (law)
This article is about the legal concept. For scientific evidence in pure science, see Scientific evidence.- Role :The educating witness teaches the fact-finder about the underlying scientific theory and instrument implementing theory...
, technical or other) opinion about an evidence
Evidence
Evidence in its broadest sense includes everything that is used to determine or demonstrate the truth of an assertion. Giving or procuring evidence is the process of using those things that are either presumed to be true, or were themselves proven via evidence, to demonstrate an assertion's truth...
or fact
Fact
A fact is something that has really occurred or is actually the case. The usual test for a statement of fact is verifiability, that is whether it can be shown to correspond to experience. Standard reference works are often used to check facts...
issue within the scope of his expertise, referred to as the expert opinion, as an assistance to the fact-finder. Expert witnesses may also deliver expert evidence about facts from the domain of their expertise. At times, their testimony may be rebutted with a learned treatise
Learned treatise
A learned treatise, in the law of evidence, is a text that is sufficiently authoritiative in its field to be admissible as evidence in a court in support of the contentions made therein....
, sometimes to the detriment of their reputations.
In Scots Law, Davie v Magistrates of Edinburgh (1953) provides authority that where a witness has particular knowledge or skills in an area being examined by the court, and has been called to court in order to elaborate on that area for the benefit of the court, that witness may give evidence of his opinion on that area.
Experts in the real world
Typically, experts are relied on for opinions on severity of injuryInjury
-By cause:*Traumatic injury, a body wound or shock produced by sudden physical injury, as from violence or accident*Other injuries from external physical causes, such as radiation injury, burn injury or frostbite*Injury from infection...
, degree of insanity
Insanity
Insanity, craziness or madness is a spectrum of behaviors characterized by certain abnormal mental or behavioral patterns. Insanity may manifest as violations of societal norms, including becoming a danger to themselves and others, though not all such acts are considered insanity...
, cause of failure in a machine or other device, loss of earnings, care costs, and the like. In an intellectual property
Intellectual property
Intellectual property is a term referring to a number of distinct types of creations of the mind for which a set of exclusive rights are recognized—and the corresponding fields of law...
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 irrelevant.
The tribunal
Tribunal
A tribunal in the general sense is any person or institution with the authority to judge, adjudicate on, or determine claims or disputes—whether or not it is called a tribunal in its title....
itself, or the judge
Judge
A judge is a person who presides over court proceedings, either alone or as part of a panel of judges. The powers, functions, method of appointment, discipline, and training of judges vary widely across different jurisdictions. The judge is supposed to conduct the trial impartially and in an open...
, can in some systems call upon experts to technically evaluate a certain fact
Fact
A fact is something that has really occurred or is actually the case. The usual test for a statement of fact is verifiability, that is whether it can be shown to correspond to experience. Standard reference works are often used to check facts...
or 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 heavy responsibility, especially in penal trials
Penal law
In the most general sense, penal is the body of laws that are enforced by the State in its own name and impose penalties for their violation, as opposed to civil law that seeks to redress private wrongs...
, and perjury
Perjury
Perjury, also known as forswearing, is the willful act of swearing a false oath or affirmation to tell the truth, whether spoken or in writing, concerning matters material to a judicial proceeding. That is, the witness falsely promises to tell the truth about matters which affect the outcome of the...
by an expert is a severely punished crime
Crime
Crime is the breach of rules or laws for which some governing authority can ultimately prescribe a conviction...
in most countries. The use of expert witnesses is sometimes criticized in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
because in civil trials
Civil law (common law)
Civil law, as opposed to criminal law, is the branch of law dealing with disputes between individuals or organizations, in which compensation may be awarded to the victim...
, they are often used by both sides to advocate differing positions, and it is left up to a jury
Jury
A jury is a sworn body of people convened to render an impartial verdict officially submitted to them by a court, or to set a penalty or judgment. Modern juries tend to be found in courts to ascertain the guilt, or lack thereof, in a crime. In Anglophone jurisdictions, the verdict may be guilty,...
of laymen 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."
Duties of experts
In England and WalesEngland and Wales
England and Wales is a jurisdiction within the United Kingdom. It consists of England and Wales, two of the four countries of the United Kingdom...
, under the Civil Procedure Rules 1998
Civil Procedure Rules 1998
The Civil Procedure Rules are the rules of civil procedure used by the Court of Appeal, High Court of Justice, and County Courts in civil cases in England and Wales...
(CPR), an expert witness is required to be independent and address his or her expert report
Expert report
An expert report is a study written by one or more experts that states findings and offers opinions.In law, expert reports are generated by expert witnesses offering their opinions on points of controversy in a legal case, and are typically sponsored by one side or the other in a litigation in...
to the court. A witness may be jointly instructed by both sides if the parties agree to this, especially in cases where the liability is relatively small.
Under the CPR, expert witnesses are usually instructed to produce a joint statement detailing points of agreement and disagreement to assist the court or tribunal. The meeting is held quite independently of instructing lawyers, and often assists in resolution of a case, especially if the experts review and modify their opinions. When this happens, substantial trial costs can be saved when the parties to a dispute agree to a settlement. In most systems, the trial
Trial (law)
In law, a trial is when parties to a dispute come together to present information in a tribunal, a formal setting with the authority to adjudicate claims or disputes. One form of tribunal is a court...
(or the procedure) can be suspended in order to allow the experts to study the case and produce their results. More frequently, meetings of experts occur before trial.
Experts charge a professional fee which is paid by the party commissioning the report (both parties for joint instructions) although the report is addressed to the court. The fee must not be contingent on the outcome of the case. Expert witnesses may be subpoenaed (issued with a witness summons), although this is normally a formality to avoid court date clashes.
History
The earliest known use of an expert witness in English law came in 1782, when a court that was hearing litigation relating to the silting-up of WellsWells-next-the-Sea
Wells-next-the-Sea, known locally simply as Wells, is a town, civil parish and seaport situated on the North Norfolk coast in England.The civil parish has an area of and in the 2001 census had a population of 2,451 in 1,205 households...
harbour in Norfolk
Norfolk
Norfolk is a low-lying county in the East of England. It has borders with Lincolnshire to the west, Cambridgeshire to the west and southwest and Suffolk to the south. Its northern and eastern boundaries are the North Sea coast and to the north-west the county is bordered by The Wash. The county...
accepted evidence from a leading civil engineer
Civil engineer
A civil engineer is a person who practices civil engineering; the application of planning, designing, constructing, maintaining, and operating infrastructures while protecting the public and environmental health, as well as improving existing infrastructures that have been neglected.Originally, a...
, John Smeaton
John Smeaton
John Smeaton, FRS, was an English civil engineer responsible for the design of bridges, canals, harbours and lighthouses. He was also a capable mechanical engineer and an eminent physicist...
. This decision by the court to accept Smeaton's evidence is widely cited as the root of modern rules on expert evidence. However, it was still such an unusual feature in court that in 1957 in the Old Bailey
Old Bailey
The Central Criminal Court in England and Wales, commonly known as the Old Bailey from the street in which it stands, is a court building in central London, one of a number of buildings housing the Crown Court...
, Lord Justice Patrick Devlin
Patrick Devlin, Baron Devlin
Patrick Arthur Devlin, Baron Devlin, PC was a British lawyer, judge and jurist. He wrote a report on Britain's involvement in Nyasaland in 1959...
could describe the case of suspected serial killer
Serial killer
A serial killer, as typically defined, is an individual who has murdered three or more people over a period of more than a month, with down time between the murders, and whose motivation for killing is usually based on psychological gratification...
Dr John Bodkin Adams
John Bodkin Adams
John Bodkin Adams was an Irish-born British general practitioner, convicted fraudster and suspected serial killer. Between the years 1946 and 1956, more than 160 of his patients died in suspicious circumstances. Of these, 132 left him money or items in their will. He was tried and acquitted for...
thus: "It is a most curious situation, perhaps unique in these courts, that the act of murder has to be proved by expert evidence."
On the other hand, expert evidence is often the most important component of many civil and criminal cases today. Fingerprint
Fingerprint
A fingerprint in its narrow sense is an impression left by the friction ridges of a human finger. In a wider use of the term, fingerprints are the traces of an impression from the friction ridges of any part of a human hand. A print from the foot can also leave an impression of friction ridges...
examination, blood analysis and DNA fingerprinting are common kinds of expert evidence heard in serious criminal cases. In civil cases, the work of accident analysis
Accident Analysis
Accident analysis is carried out in order to determine the cause or causes of an accident or series of accidents so as to prevent further incidents of a similar kind. It is also known as accident investigation. It may be performed by a range of experts, including forensic scientists, forensic...
, forensic engineers, and forensic accountants is usually important, the latter to assess damages
Damages
In law, damages is an award, typically of money, to be paid to a person as compensation for loss or injury; grammatically, it is a singular noun, not plural.- Compensatory damages :...
and costs in long and complex cases. Intellectual property
Intellectual property
Intellectual property is a term referring to a number of distinct types of creations of the mind for which a set of exclusive rights are recognized—and the corresponding fields of law...
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.
Non-testifying experts
In the U.S., a party can hire experts to help him/her evaluate the case. For example, a car maker may hire an experienced mechanic to decide if its cars were built to specification. This kind of expert opinion will be protected from discoveryDiscovery (law)
In U.S.law, discovery is the pre-trial phase in a lawsuit in which each party, through the law of civil procedure, can obtain evidence from the opposing party by means of discovery devices including requests for answers to interrogatories, requests for production of documents, requests for...
. If the expert finds something that is against its client, the opposite party will not know it. This privilege is similar to the work product
Work product
Work product is something created by an employee that is considered to become the property of the employer -- for instance, a design, patentable process, recipe, etc. -- given certain conditions. It becomes trickier when the employment relationship is one of contractor-client...
protected by the attorney/client privilege. The non-testifying expert can be present at trial or hearing to aid the attorney in asking questions of other expert witnesses.
Testifying experts
If the witness needs to testify in court, the privilege is no longer protected. The expert witness's identity and nearly all documents used to prepare the testimony will become discoverable. Usually an experienced lawyer will advise the expert not to take notes on documents because all of the notes will be available to the other party.An expert testifying in court must satisfy the requirements of Fed. R. Evid. 702. Generally, under Rule 702, an expert is a person with “scientific, technical, or other specialized knowledge" who can "assist the trier of fact,” which is typically a jury. A qualified expert may testify “in the form of an opinion or otherwise” so long as: “(1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case.”
Although experts can testify in any case in which their expertise is relevant, criminal cases are more likely to use forensic scientists or forensic psychologists
Forensic psychology
Forensic psychology is the intersection between psychology and the criminal justice system. It involves understanding criminal law in the relevant jurisdictions in order to be able to interact appropriately with judges, attorneys and other legal professionals...
, whereas civil cases, such as personal injury, may use forensic engineers, forensic accountants, employment consultant
Employment consultant
An employment consultant is an expert witness who advises courts and tribunals on employment related issues such as earnings, labour market analysis, residual earning capacity, and retraining. The main area involved is that of personal injury litigation where loss of earnings is an important...
s or care
Health care
Health care is the diagnosis, treatment, and prevention of disease, illness, injury, and other physical and mental impairments in humans. Health care is delivered by practitioners in medicine, chiropractic, dentistry, nursing, pharmacy, allied health, and other care providers...
experts. Senior physician
Physician
A physician is a health care provider who practices the profession of medicine, which is concerned with promoting, maintaining or restoring human health through the study, diagnosis, and treatment of disease, injury and other physical and mental impairments...
s – UK, Ireland, and Commonwealth consultant
Consultant (medicine)
In the United Kingdom, Republic of Ireland, and parts of the Commonwealth, consultant is the title of a senior doctor who has completed all of his or her specialist training and been placed on the specialist register in their chosen specialty...
s, U.S. attending physician
Attending physician
In the United States, an attending physician is a physician who has completed residency and practices medicine in a clinic or hospital, in the specialty learned during residency. An attending physician can supervise fellows, residents, and medical students...
s – are frequently used in both the civil and criminal courts.
The Federal Court of Australia has issued guidelines for experts appearing in Australian courts. This covers the format of the expert's written testimony as well as their behaviour in court. Similar procedures apply in non-court forums, such as the Australian Human Rights and Equal Opportunity Commission.
See also
- Ambush defenceAmbush defenceAn ambush defence is one in which defence evidence - notably from expert witnesses - has not been adduced in advance to the prosecuting authorities, leading to their inability to rebut it. The term is used in United Kingdom jurisprudence...
- Daubert StandardDaubert StandardThe Daubert standard is a rule of evidence regarding the admissibility of expert witnesses' testimony during United States federal legal proceedings. Pursuant to this standard, a party may raise a Daubert motion, which is a special case of motion in limine raised before or during trial to exclude...
and Daubert v. Merrell Dow PharmaceuticalsDaubert v. Merrell Dow PharmaceuticalsDaubert v. Merrell Dow Pharmaceuticals, is a United States Supreme Court case determining the standard for admitting expert testimony in federal courts... - Death of an Expert WitnessDeath of an Expert WitnessDeath of an Expert Witness is an Adam Dalgliesh novel by P. D. James, published in 1977. It begins with the discovery of a murder of young girl. However, this is not the focus of the novel, but rather is used as a method to introduce us to the staff of a forensic laboratory, the background of this...
- a novel - Employment consultantEmployment consultantAn employment consultant is an expert witness who advises courts and tribunals on employment related issues such as earnings, labour market analysis, residual earning capacity, and retraining. The main area involved is that of personal injury litigation where loss of earnings is an important...
- Expert shoppingExpert shoppingExpert shopping is the practice of finding an expert on a given subject whose professional opinion is skewed toward the answer that the searching party already prefers...
- ExpertpagesExpertpagesExpertpages is a free directory website of U.S. expert witnesses founded in 1995. As the first online directory for experts, expert witnesses and consultants, it has received accolades of being the “best free directory” by Lawyer’s Weekly USA and as being “one of the best sites in its field” by...
- Forensic accountantForensic accountantForensic accountants are experienced auditors, accountants, and investigators of legal and financial documents that are hired to look into possible suspicions of fraudulent activity within a company; or are hired by a company who may just want to prevent fraudulent activities from occurring...
- Forensic economicsForensic economicsForensic economics is the scientific discipline that applies economic theories and methods to the issue of pecuniary damages as specified by case law and legislative codes...
- Forensic engineeringForensic engineeringForensic engineering is the investigation of materials, products, structures or components that fail or do not operate or function as intended, causing personal injury or damage to property. The consequences of failure are dealt with by the law of product liability. The field also deals with...
- Forensic science
- Forensic psychologyForensic psychologyForensic psychology is the intersection between psychology and the criminal justice system. It involves understanding criminal law in the relevant jurisdictions in order to be able to interact appropriately with judges, attorneys and other legal professionals...
- Forensic video analysis
- Gibson's lawGibson's lawIn public relations,and in the practice of law, Gibson's law holds that "For every PhD there is an equal and opposite PhD."The term specifically refers to the conflict between testimony of expert witnesses called by opposing parties in a trial under an adversarial system of justice.It is also...
- In limineIn limineMotion in limine is a legal written "request" or motion to a judge which can be used for civil or criminal proceedings and at the State or Federal level. A frequent use is at a pre-trial hearing or during an actual trial requesting that the judge rule that certain testimony regarding evidence or...
- Jones v KaneyJones v KaneyJones v Kaney [2011] UKSC 13 is a 2011 decision of the Supreme Court of the United Kingdom on whether expert witnesses retained by a party in litigation can be sued for professional negligence, or whether they have the benefit of immunity from suit...
— English caselaw abolishing witness immunity from civil action for negligence - Kumho Tire Co. v. CarmichaelKumho Tire Co. v. CarmichaelKumho Tire Co. v. Carmichael, , is a United States Supreme Court case that applied the Daubert standard to expert testimony from non-scientists.-Facts of the case:...
- Questioned document examinationQuestioned document examinationQuestioned document examination is the forensic science discipline pertaining to documents that are in dispute in a court of law...
- R. v. MohanR. v. MohanR. v. Mohan [1994] 2 S.C.R. 9 is a leading Supreme Court of Canada decision on the use of experts in trial testimony.-Background:Dr. Chikmaglur Mohan was a pediatrician in North Bay, Ontario. He was charged with sexual assault of four teenaged patients. During his trial, the defence tried to put...
— Canadian caselaw establishing qualifications for expert witnesses - Ultimate issueUltimate issue (law)An ultimate issue in criminal law is a legal issue at stake in the prosecution of a crime for which an expert witness is providing testimony.-Example:...
- Vehicular accident reconstructionVehicular accident reconstructionVehicular accident reconstruction is the scientific process of investigating, analyzing, and drawing conclusions about the causes and events during a vehicle collision...
External links
- Experts & Institutions: Centre for the study of expert knowledge in law and society http://www2.hull.ac.uk/discover/eai.aspx
- Expert Testimony in Federal Civil Trials: A Preliminary Analysis (pdf) (Federal Judicial Center, 2000)
- Project on Scientific Knowledge and Public Policy. Daubert-The Most Influential Supreme Court Ruling You've Never Heard Of (pdf)
- Kenton K. Yee, Dueling Experts and Imperfect Verification, 28.4 International Review of Law and Economics, 246-255 (2008)