How accurate is a polygraph?

U.S. Government studies have concluded that when a qualified examiner conducts the test properly, the polygraph exam is between 87 and 95 percent accurate. It is the most accurate means available for determining the truth or deception of a person answering a direct question.



What is measured by a polygraph?

A standard polygraph records changes in physiological signs. These signs include blood pressure, heart rate, breathing, and sweat gland activity (galvanic skin reflex).


It does not matter that the examinee is nervous during testing; some nervousness is to be expected. The polygraph records significant changes from the examinee’s baseline or normal reading when specific questions are asked.


An examinee intending deception when answering a particular question activates their sympathetic nervous system when that question is asked. This will cause identifiable changes in one or more of the physical responses that is measured by the polygraph.


Is the polygraph admissible in court?  Each jurisdiction must be checked to determine admissibility standards; some courts allow the introduction of polygraph evidence while others have not. In most cases, polygraph evidence is used during pre-trial investigation and preparations rather than during the actual trial.


In the O. J. Simpson civil trial, the results of a polygraph were admitted into evidence. This established a precedent across the nation allowing polygraph examinations in civil trials such as divorce cases.


Can an employer require an employee take to the test?


Yes, under certain conditions.


The Employee Polygraph Protection Act of 1988 requires:


1) That the employer has suffered a specific economic loss of money or merchandise and the loss has been reported to the appropriate authorities.


2) That the employee to be tested had access to the missing property or loss.


3) And that the employee is suspected of involvement in the missing property or loss beyond mere access.


If these conditions exist and the employer desires to have an employee tested, the employer must make the request in writing. This form can be downloaded from our website and must be printed on the employer’s letterhead. This request must advise the employee that the exam is voluntary and that no action can be taken against him/her solely for refusing to take it.


The employee must also be advised of the incident under investigation, his/her legal rights, and a number of other notifications required under the law. This request must be presented to the employee at least 2 business days prior to the scheduled exam.


Questions must be limited to the specific loss only. The examiner is not permitted to ask questions about losses other than those listed in the notification form.


If an employee “fails” a polygraph under these conditions, the employer still may not take action against the employee without additional supporting evidence indicating the employee’s involvement in the loss.


Exemptions granted by The Employee Polygraph Protection Act of 1988 allow pre-employment polygraph examinations for employees of banks, hospitals, nursing homes, drug warehouses, armored car companies and law enforcement agencies. If you have questions about pre-employment polygraph screening for your employees, please contact us.


What is the Employee Polygraph Protection Act? (EPPA)


See the American Polygraph Association comprehensive page on this subject by clicking here.


 What is the scope of test questions?


Prohibitive Inquiries – Personal and intrusive questions have no place In a properly conducted polygraph examination. Many state licensing laws, the Employee Polygraph Protection Act, as well as the American Polygraph Association, has so stated in language similar to the following:




  • religious beliefs or affiliations
  • beliefs or opinions regarding racial matters
  • political beliefs or affiliations
  • beliefs, affiliations or lawful activities regarding unions or labor organizations
  • sexual preferences or activities


In a law enforcement pre-employment polygraph examination, the questions focus on such

job related inquiries as the theft of money or merchandise from previous employers,

falsification of information on the job applications, the use of illegal drugs during

working hours and criminal activities. The test questions are limited in the time span they

cover, and all are reviewed and discussed with the examinee during a pre-test interview

before any polygraph testing is done. There are no surprise or trick questions.


In a specific issue polygraph examination the relevant questions focus on the particular act

under investigation.



Who gets the test results?


According to the various state licensing laws and the American Polygraph Association’s Standards and Principles of Practice, polygraph results can be released only to authorized persons. Generally those individuals who can receive test results are the examinee, and anyone specifically designated in writing by the examinee, the person, firm, corporation or governmental agency which requested the examination, and others as may be required by due process of law.



What legislation dictates polygraph?


Licensing: Currently there are 29 states and 3 counties that have laws requiring licensure or certification for polygraph examiners. Most laws require formal instruction, an internship-training period and successful completion of a licensing examination. For example, the following are basic requirements for licensure in one state:


A person is qualified to receive a license as an examiner:


  • who establishes that he or she is a person of good moral character; and,
  • who has passed an examination conducted by the Licensing Committee, or under its supervision. to determine his or her competency to obtain a license to practice as an examiner and
  • who has conferred upon him or her an academic degree, at the baccalaureate level, from an accredited collect or university; and,
  • who has satisfactorily completed 6 months of study in the detection of deception, as prescribed by rule.


Prohibitive Legislation: In addition to the Employee Polygraph Protection Act, to date there are 20 states and the District of Columbia, which have enacted legislation, designed to regulate an employer’s use of the polygraph. No state prohibits polygraph testing in all settings. A typical statute states: No employer may require a prospective or current employee to take a polygraph examination as a condition of employment or continued employment.


Most of these states make exceptions for testing of certain occupational groups. Commonly exempted are law enforcement agencies and companies that manufacture, distribute or dispense drugs and controlled substances.


The American Polygraph Association has consistently supported licensing efforts throughout the country. The APA encourages efforts to establish proper qualifications for polygraph examiners and criteria for testing procedures.


The Employee Polygraph Protection Act of 1988 prohibits much, but not all pre-employment polygraph testing. Testing of employees is permitted to solve an employer’s “economic loss.” There are exemptions for guards, armored car personnel and those who handle drugs and narcotics. EPPA does not affect testing for attorneys or local, state or federal agencies.




Polygraph results (psychophysiological detection of deception examinations) are admissible in some federal circuits and some states. More often, such evidence is admissible where the parties have agreed to their admissibility before the examination is given, under terms of a stipulation. Some jurisdictions have absolute bans on admissibility of polygraph results as evidence and even the suggestion that a polygraph examination is involved is sufficient to cause a retrial. The United States Supreme Court has yet to rule on the issue of admissibility, so the rules in federal circuits vary considerably. The Supreme Court has said, in passing, that polygraph examinations raise the issue of Fifth Amendment protection, [Schmerber v. California, 86 S. Ct. 1826 (l966).] The Supreme Court has also held that a Miranda warning before a polygraph examination is sufficient to allow admissibility of a confession that follows an examination, [Wyrick v. Fields, 103 S. Ct. 394 (1982).] In 1993, the Supreme Court removed the restrictive requirements of the 1923 Frye decision on scientific evidence and said Rule 702 requirements were sufficient, [Daubert v. Mettell Dow Pharmaceutcals, 113 S.ct. 2786.]Daubert did not involve lie detection, per se, as an issue, as Frye did, but it had a profound effect on admissibility of polygraph results as evidence, when proffered by the defendants under the principles embodied in the Federal Rules of Evidence expressed in Daubert, see [United States v. Posado (5th Cir. 1995) WL 368417.] Some circuits already have specific rules for admissibility, such as the 11th Circuit that specifies what must be done for polygraph results to be admitted over objection, or under stipulation, [United States v. Piccinonna 885 F.2d 1529 (11th Cir. 1989).] Other circuits have left the decision to the discretion of the trial judge. The rules that states and federal circuits generally follow in stipulated admissibility were established in [State v. Valdez, 371 P.2d 894 (Arizona, 1962).] The rules followed when polygraph results are admitted over objection of opposing counsel usually cite [State v. Dorsey, 539 P.2d 204 (New Mexico, 1975).] Primarily because of Daubert, as well as the impact the other cited cases have had, polygraph examination admissibility is changing in many states. Many appeals, based on the exclusion of polygraph evidence at trial are now under review by appellate courts.


Representative case citations are provided for reference:



Clements v. State, 474 So.2d 695 (1984).

Green v. Am. Cast Iron, 464 so.2d 294 (1984).



State v. Valdez, 91 Ariz.. 274, 371, P.2d 894 (1962).

State v. Molina, 117 Ariz. 4541 573 P.2d 528 (App.1977).



Hays v. State, 767 S.W.2d 525 (1989).



People v. Houser, 85 Cal.App.2d 686, 193 P.2d 937 (1948)

Robinson v. Wilson, 44 Cal.App.3d 92, 118 Cal.Rptr. 569 (1974).

Witherspoon v. Superior Court, 133 Cal.App.3rd 24 (1982)



Williams v. State, 378 A.2nd 117 (1977).



State v. Chambers, 240 Ga. 76, 239 SE.2d 324 (1977).

Miller v. State, 380 S.E.2d 690 (1989).



State v. Fain, 774 P.2d 252 (1989).



Barnes v. State, 537 N.E.2d 489 (1989).

Davidson v. State, 558 N.E.2d 1077 (1990).



State v. McNamara, 104 N.W.2d 568 (1960).

Haldeman v. Total Petroleum, 376 N.W.2d 98 (1985).



State v. Roach, 570P.2d 1082 (1978).



Corbett v. State, 584 P.2d 704 (1978).


New Jersey:

State v. McDavitt, 297 A.2d 849 (1972).

State v. McMahon 524 A.2d 1348 (1986).


New Mexico:

State v. Dorsey, 539 P.2ed 204 (1975).


North Dakota:

State v. Newman, 409 N.W.2d 79 (1987).



Moss v. Nationwide, 493 N.E.2d 969 (1985).

State v. Souel, 372 N.E.2d 1318 (1978).



State v. Jenkins, 523 P.2d 1232 (1974).

State v. Rebetevano, 681 P.2d 1265 (1984).



State v. Grigsby, 647 P.2d 6 (1982).



Cullin v. State, 565 P.2d 445 (1977).