An instrument used to measure physiological responses in humans when they are questioned in order to determine if their answers are truthful.
Also known as a "lie detector," the polygraph has a controversial history in U.S. law. First developed in the late nineteenth century, its modern incarnation is an electromechanical device that is attached to a subject's body during an interview. The discipline of polygraphy is based on the theory that by recording involuntary physiological changes in the subject, the polygraph yields data that can be interpreted to determine whether the subject is telling the truth. Supporters of the scientific validity of the polygraph claim that results are approximately 90 percent accurate. For much of the twentieth century, however, polygraph evidence was inadmissible in criminal cases on grounds of unreliability. Polygraph evidence was admissible in civil cases, however, and it was also used widely in law enforcement, government, and industry.
Polygraphy uses a variety of formats. Until the 1950s the format was the relevant/irrelevant (R/I) test; it rested on the now discredited belief that a subject produces a specific identifiable physiological response when lying. The R/I test has been replaced by the control question (CQ) format, the only format routinely used in forensic tests. Typically, a trained examiner fits a subject with sensors to measure respiration, heart rate and blood pressure, and perspiration, which the polygraph records using pens on graph paper. The examiner asks a series of questions, including control questions that are designed to provoke anxiety and denial. Later, another examiner compares these answers with answers pertaining to the matter at hand. This is known as numerical CQ testing. So-called global CQ testing includes a more subjective component: one examiner scores the test while also factoring in the subject's observable physical responses, such as movement, expression, and voice.
In U.S. courts, the use of the polygraph was first addressed in 1923. In refusing to admit polygraph evidence in a murder case, the Court of Appeals for the District of Columbia created a legal standard that would last for nearly 70 years (Frye v. United States, 54 App. D.C. 46, 293 F. 1013 ). This standard came to be known as the Frye rule, or general acceptance test. To be admissible in court, novel SCIENTIFIC EVIDENCE first must have gained general acceptance in its scientific field.
The Frye rule applied broadly to all scientific evidence, including polygraph evidence. Other appellate courts followed the court's standard throughout most of the century, primarily because polygraphy never gained widespread acceptance among scientists. Nonetheless, polygraph evidence was used in civil lawsuits, and police agencies, businesses, and government offices continued to use the polygraph regularly to provide evidence, screen job applicants, and investigate security risks.
Advances in polygraphy helped spur a judicial reevaluation, but more important was the adoption of the FEDERAL RULES OF EVIDENCE in the 1970s. Rule 702 set an important new standard for the admission of scientific evidence:
If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise.
Over the next two decades, appellate courts authorized use of polygraph evidence in a few state courts, a trend followed by the U.S. Court of Appeals for the Eleventh Circuit and the military courts. Then, in 1993, in a case not specifically related to the polygraph, the U.S. Supreme Court held that Rule 702 replaced the Frye test (Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 113 S. Ct. 2786, 125 L. Ed. 2d 469). In essence, the Court said that the standard of general scientific acceptance was not as important as whether EXPERT TESTIMONY can assist jurors. Soon thereafter, several federal courts reconsidered their long-standing ban on polygraph evidence and determined that they now had the discretion to permit its introduction at trial.
Congress also reexamined the use of the polygraph in industry. In 1988, lawmakers responded to civil liberty concerns about the abuse of polygraph testing in private industry by passing the Employee Polygraph Protection Act (29 U.S.C.A. §§ 2001 et seq.). The law bars preemployment testing in banking, retail, and other private industries and also makes it illegal for employers to fire, discriminate against, or discipline employees who refuse to submit to polygraph tests. The act exempts government employers, private industry when an employee is under investigation for economic injury suffered by the employer, and all security services and industries that manufacture, distribute, or dispense controlled substances.
In military trials, the situation was different. In United States v. Scheffer, 523 U.S. 303, 118 S. Ct. 1261, 140 L. Ed. 2d 413 (1998), the Supreme Court addressed the claim of airman Edward G. Scheffer that prohibiting the introduction of polygraph evidence during his COURT-MARTIAL (military criminal trial) violated his constitutional rights. Under Military Rule of Evidence 707, polygraph evidence is not allowed in court-martial proceedings. So, although Scheffer, who was accused of, among other things, taking illegal drugs, passed a polygraph, it was inadmissible as evidence. A federal court of appeals reversed the court-martial, stating that excluding the polygraph evidence did, in fact, violate Scheffer's right to present a defense as guaranteed by the SIXTH AMENDMENT. Upon review, the Supreme Court upheld Military Rule of Evidence 707. In the opinion of the Court, "State and federal governments unquestionably have a legitimate interest in ensuring that reliable evidence is presented to the trier of fact in a criminal trial." However, "there is simply no consensus that polygraph evidence is reliable."