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What Is The Polygraph?
WHAT IS THE POLYGRAPH?
A polygraph is an instrument that simultaneously records changes in physiological processes such as heartbeat, blood pressure, and respiration. The polygraph is used as a lie detector by police departments, the FBI, the CIA, federal and state governments, and numerous private agencies. The underlying theory of the polygraph is that when people lie they also get measurably nervous about lying. The heartbeat increases, blood pressure goes up, breathing rhythms change, perspiration increases, etc. A baseline for these physiological characteristics is established by asking the subject questions whose answers the investigator knows. Deviation from the baseline for truthfulness is taken as sign of lying.
There are three basic approaches to the polygraph test:
1.The Control Question Test (CQT). This test compares the physiological response to relevant questions about the crime with the response to questions relating to possible prior misdeeds. "This test is often used to determine whether certain criminal suspects should be prosecuted or classified as uninvolved in the crime" (APA).
2.The Directed Lie Test (DLT). This test tries to detect lying by comparing physiological responses when the subject is told to deliberately lie to responses when they tell the truth.
3.The Guilty Knowledge Test (GKT). This test compares physiological responses to multiple-choice type questions about the crime, one choice of which contains information only the crime investigators and the criminal would know about.
Is there evidence the polygraph is really able to detect lies?
The machine measures changes in blood pressure, breath rate, and respiration rate. When a person lies it is assumed that these physiological changes occur in such a way that a trained expert can detect whether the person is lying. Is there a scientific formula or law which establishes a regular correlation between such physiological changes and lying? No. Is there any scientific evidence that polygraph experts can detect lies using their machine at a significantly better rate than non-experts using other methods? No. There are no machines and no experts that can detect with a high degree of accuracy when people, selected randomly, are lying and when they are telling the truth.
The polygraph pens don't do a special dance when a person lies. The polygrapher scores the test by comparing physiological responses (breathing, blood pressure, heart, and perspiration rates) to these probable-lie control questions with reactions to relevant questions such as, "Did you ever use an illegal drug?" (commonly asked in pre-employment screening). If the former reactions are greater, the examinee passes; if the latter are greater, he fails. If responses to both "control" and relevant questions are about the same, the result is deemed inconclusive.
The test also includes irrelevant questions such as, "Are the lights on in this room?" The polygrapher falsely explains that such questions provide a "baseline for truth," because the true answer is obvious. But in reality, they are not scored at all! They merely serve as buffers between pairs of relevant and "control" questions
HOW IT WORKS
A polygraph instrument is basically a combination of medical devices that are used to monitor changes occurring in the body. As a person is questioned about a certain event or incident, the examiner looks to see how the person's heart rate, blood pressure, respiratory rate and electro-dermal activity (sweatiness, in this case of the fingers) change in comparison to normal levels. Fluctuations may indicate that person is being deceptive, but exam results are open to interpretation by the examiner.
Polygraph exams are most often associated with criminal investigations, but there are other instances in which they are used. You may one day be subject to a polygraph exam before being hired for a job: Many government entities, and some private-sector employers, will require or ask you to undergo a polygraph exam prior to employment.
Polygraph examinations are designed to look for significant involuntary responses going on in a person's body when that person is subjected to stress, such as the stress associated with deception. The exams are not able to specifically detect if a person is lying, according to polygrapher Dr. Bob Lee, former executive director of operations at Axciton Systems, a manufacturer of polygraph instruments. But there are certain physiological responses that most of us undergo when attempting to deceive another person. By asking questions about a particular issue under investigation and examining a subject's physiological reactions to those questions, a polygraph examiner can determine if deceptive behavior is being demonstrated.
How does the test process work?
a: The examiner receives and reviews the facts surrounding the case.
b: The examiner explains the test process to the subject and reviews the case facts during the pretest interview.
c: The examiner designs the specific test questions and reads each question to the subject to make sure each one is easily understood.
d: The test subject is attached to the polygraph instrument and given additional instructions.
e: The questions are read to the subject several times while he/she is attached to the polygraph sensors.
f: After all charts (polygrams) have been run, the examiner analyzes the charts and develops a numerical score for the test. This score results in a conclusion of either truthful, deceptive or inconclusive.
g: The examiner will transmit the test results to the client verbally, usually within 24 hours. A written report may be requested, however some examiners will charge a small fee for this report.
NOTE: Polygraph exams are conducted in private with no other persons permitted in the examination room during the test (other than possibly an interpreter) . NOTE: The average polygraph exam takes from one to three hours to complete.
WHAT IS THE POLYGRAPH?
A polygraph is an instrument that simultaneously records changes in physiological processes such as heartbeat, blood pressure, and respiration. The polygraph is used as a lie detector by police departments, the FBI, the CIA, federal and state governments, and numerous private agencies. The underlying theory of the polygraph is that when people lie they also get measurably nervous about lying. The heartbeat increases, blood pressure goes up, breathing rhythms change, perspiration increases, etc. A baseline for these physiological characteristics is established by asking the subject questions whose answers the investigator knows. Deviation from the baseline for truthfulness is taken as sign of lying.
There are three basic approaches to the polygraph test:
1.The Control Question Test (CQT). This test compares the physiological response to relevant questions about the crime with the response to questions relating to possible prior misdeeds. "This test is often used to determine whether certain criminal suspects should be prosecuted or classified as uninvolved in the crime" (APA).
2.The Directed Lie Test (DLT). This test tries to detect lying by comparing physiological responses when the subject is told to deliberately lie to responses when they tell the truth.
3.The Guilty Knowledge Test (GKT). This test compares physiological responses to multiple-choice type questions about the crime, one choice of which contains information only the crime investigators and the criminal would know about.
Is there evidence the polygraph is really able to detect lies?
The machine measures changes in blood pressure, breath rate, and respiration rate. When a person lies it is assumed that these physiological changes occur in such a way that a trained expert can detect whether the person is lying. Is there a scientific formula or law which establishes a regular correlation between such physiological changes and lying? No. Is there any scientific evidence that polygraph experts can detect lies using their machine at a significantly better rate than non-experts using other methods? No. There are no machines and no experts that can detect with a high degree of accuracy when people, selected randomly, are lying and when they are telling the truth.
The polygraph pens don't do a special dance when a person lies. The polygrapher scores the test by comparing physiological responses (breathing, blood pressure, heart, and perspiration rates) to these probable-lie control questions with reactions to relevant questions such as, "Did you ever use an illegal drug?" (commonly asked in pre-employment screening). If the former reactions are greater, the examinee passes; if the latter are greater, he fails. If responses to both "control" and relevant questions are about the same, the result is deemed inconclusive.
The test also includes irrelevant questions such as, "Are the lights on in this room?" The polygrapher falsely explains that such questions provide a "baseline for truth," because the true answer is obvious. But in reality, they are not scored at all! They merely serve as buffers between pairs of relevant and "control" questions
HOW IT WORKS
A polygraph instrument is basically a combination of medical devices that are used to monitor changes occurring in the body. As a person is questioned about a certain event or incident, the examiner looks to see how the person's heart rate, blood pressure, respiratory rate and electro-dermal activity (sweatiness, in this case of the fingers) change in comparison to normal levels. Fluctuations may indicate that person is being deceptive, but exam results are open to interpretation by the examiner.
Polygraph exams are most often associated with criminal investigations, but there are other instances in which they are used. You may one day be subject to a polygraph exam before being hired for a job: Many government entities, and some private-sector employers, will require or ask you to undergo a polygraph exam prior to employment.
Polygraph examinations are designed to look for significant involuntary responses going on in a person's body when that person is subjected to stress, such as the stress associated with deception. The exams are not able to specifically detect if a person is lying, according to polygrapher Dr. Bob Lee, former executive director of operations at Axciton Systems, a manufacturer of polygraph instruments. But there are certain physiological responses that most of us undergo when attempting to deceive another person. By asking questions about a particular issue under investigation and examining a subject's physiological reactions to those questions, a polygraph examiner can determine if deceptive behavior is being demonstrated.
How does the test process work?
a: The examiner receives and reviews the facts surrounding the case.
b: The examiner explains the test process to the subject and reviews the case facts during the pretest interview.
c: The examiner designs the specific test questions and reads each question to the subject to make sure each one is easily understood.
d: The test subject is attached to the polygraph instrument and given additional instructions.
e: The questions are read to the subject several times while he/she is attached to the polygraph sensors.
f: After all charts (polygrams) have been run, the examiner analyzes the charts and develops a numerical score for the test. This score results in a conclusion of either truthful, deceptive or inconclusive.
g: The examiner will transmit the test results to the client verbally, usually within 24 hours. A written report may be requested, however some examiners will charge a small fee for this report.
NOTE: Polygraph exams are conducted in private with no other persons permitted in the examination room during the test (other than possibly an interpreter) . NOTE: The average polygraph exam takes from one to three hours to complete.