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Employee Lie Detector Tests

The polygraph examination, popularly called the "lie detector," is an arbiter of truth by employers and law enforcement in America. This is in spite of the fact that polygraph exams are not accepted as evidence in any court aside from New Mexico. They are generally unreliable for assessing whether someone is lying or telling the truth.

The American Polygraph Association, considered the leading training and accreditation agency in the world, states that polygraph equipment is seldom more than 80-90% reliable. A background check or pre-employment screening test is equally reliable for assessing an applicant's honesty and reliability.

How the Polygraph Works

Despite the popular name of lie detector, a polygraph cannot tell if someone is lying. The machine measures four to six physiological responses, such as respiration, blood pressure, and heart rate. The theory is that lying causes stress reactions, which a trained examiner analyzes.

A polygraph exam takes about an hour and a half to two hours. The examiner interviews the subjects to understand their speech patterns and reactions. It also helps the subject get comfortable with the examiner so that simple nervousness does not affect the test.

The examiner puts the measuring equipment on the subject and begins the exam. The examiner marks the graphs when they ask a relevant question. Any significant change in the measurements is taken as a sign of stress and an indication of lying.

How the Polygraph Does Not Work

According to the American Psychological Association, polygraph examiners conduct tests in two different ways. The standard method is the control question test, where they ask subjects several innocuous questions and then a relevant question. Truthful subjects have less anxiety about relevant questions because they know they are innocent of the alleged crime. The guilty knowledge test asks questions that only someone with actual knowledge of the crime would know.

The difficulty with assessing either test is that polygraphs have not been, and possibly cannot be, tested in any way to determine if they are testing a valid physical response. The accuracy of any given test may depend as much on the subject's belief in the test as it does on the test itself.

According to the American Psychological Association, "Research on the processes involved in [control question test] polygraph examinations suggests that several examiner, examinee, and situational factors influence test validity...There is little research on the effects of subjects' differences in such factors as education, intelligence, or level of autonomic arousal."

The Employee Polygraph Protection Act

These doubts and conflicting reports led to the passage of the Employee Polygraph Protection Act (EPPA) in 1988. This federal law prevents the use of lie detectors for pre-employment screening or for using the results against workers in employment. Small business owners may not:

  • Require any employee or applicant to take a lie detector test
  • Make a lie detector test a condition of employment or continued employment
  • Use the results of a lie detector test to refuse to hire, discharge, discipline, or fail to promote an employee
  • Refuse to hire, discharge, discipline, or fail to promote an employee for refusing to take a lie detector test

The EPPA does not apply to state or federal government employees.

When You May Use a Lie Detector Test

Private employers can use polygraph exams in some cases. There is a national security exception for private employers in the security business. Armored transport and security companies can use polygraph exams for employees guarding high-value infrastructure, commodities, and currency.

When employers have suffered an economic loss due to theft, embezzlement, or similar crimes, the EPPA allows the use of lie detector tests under strict conditions. Employers must:

  • Use a certified polygraph examiner
  • Have suffered actual economic loss
  • Provide the employee with a notice before the test explaining the incident leading to the investigation and why certain employees are being tested

The notice must state, at the minimum:

  • A description of the loss or injury to the business
  • An explanation of the grounds for the employer's reasonable suspicion of the employee's involvement in the incident
  • An explanation of the employee's access to the property or loss under investigation
  • An explanation of the nature and characteristics of the polygraph exam itself
  • An explanation of the employee's rights, including their right to terminate the exam, their right to consult legal counsel before the exam, and to file a complaint with the Department of Labor

Employers must provide written notice of the date, time, and location of the examination. They must give the examiner written notice identifying the employees for testing. If employers are subject to the EPPA, they must have an EPPA poster visible with other labor law posters and notices.

When You May Not Use a Polygraph

Employers cannot use polygraph tests to screen job applicants except for the positions listed above. Lie detector evidence is almost always prohibited in court, so even in cases of theft you will not be able to use the results against your employee.

Employers cannot give polygraphs in the regular course of employment to check for overall employee honesty. Current employers may not ask for the results or use the existence of a polygraph against an applicant who mentions receiving a polygraph at a previous job.

Other Methods of Getting the Truth

The use of lie detector tests for pre-employment interviews is an inefficient method of evaluating a prospective employee. The American Polygraph Association stresses that polygraphs are helpful for determining truth or falsity about a single fact-specific incident but not about anything such as tendencies, thoughts, opinions, or attitudes. For instance, a polygraph test could ask someone, "Did you steal money from your boss?" but could not ask, "Would you steal money from your boss?"

Voice stress analyzers are the new fad in police interrogation, and some employers have begun using them. They suffer the same drawbacks as lie detectors. Since the analyzers test for undetectable changes in pitch and tone, it's unclear what they are testing. Until there is better evidence or reliable case law, employers should steer clear of these devices and apps.

These alternative methods for assessing a job applicant should warrant an employer's consideration. They provide a better view of an individual's psyche, especially when paired with other tests.

  • Integrity tests: These tests purport to measure an employee's honesty and trustworthiness. Some studies suggest they tend to misclassify honest employees. Improperly worded questions can run afoul of other federal regulations.
  • Personality tests: Based on psychological evaluations, or even the tests themselves, these tests assess individuals' mental quirks and how they work individually and with groups. Tests like the MMPI have been challenged in court as violating the Americans with Disabilities Act.
  • Emotional intelligence tests: These test how an individual reacts to others and stressful situations. These tests can help evaluate team-building and management potential in prospective employees.

In general, personality testing is helpful but must be undertaken by professionals with a high degree of training. The Society for Human Resource Management (SHRM) recommends consulting both psychiatric and legal professionals before using pre-employment screening tests.

Catching Liars in the Act

For cases when you need to ask an employee questions about a theft—the other reason you might need a lie detector—take your cues from people who know how to talk to liars.

The U.S. government's High-Value Detainee Interrogation Group (HIG) developed a method of spotting liars almost every time. They also learned how to get the information they needed.

  • Be polite: A person who's done something wrong expects mistrust and accusations. The HIG found that being friendly puts them off guard and makes them open up.
  • Be prepared: Remember that the EPPA requires you to have reasonable suspicion of this worker's involvement in the crime. Have all that evidence when you or your investigator talk to the employee. Know the answers before you ask the questions.
  • Use your evidence strategically: One of the polygraph exam strategies is asking a series of innocuous questions and then asking a relevant question. If the employee is being untruthful, this locks them into their lie.
  • Be unexpected: Someone who is not telling the truth has a set of answers to questions they expect. For instance, an underage kid trying to get into a bar expects the bouncer to ask, "How old are you?" not "What is your birthdate?" or even worse, "How old were you in 2022?" Ask a question in a way they don't expect, and see if there is a pause as they try to come up with an answer.

This method takes some time. As with any interview, you must advise your employee of their rights and the reason for the questioning.

Other Legal Requirements

State laws vary as to whether polygraphs are permissible in court. All states except for New Mexico prohibit the use of polygraph evidence unless both parties agree in writing and the judge admits it.

States also have differing laws regarding the use of polygraphs in employment settings. In some states, you may not even mention polygraphs during a job interview. In other states, you must tell the prospective employee in writing that refusing or failing to pass the polygraph will not affect their chances for employment.

The U.S. Department of Labor has jurisdiction over violations of the EPPA. It can bring legal action against private employers who violate the law. Penalties can include civil fines and penalties, required employment or re-employment of the individual, promotion, and payment of lost wages.

See FindLaw's Employment Law and Human Resources page to learn more.

Hiring an Employment Law Attorney

If you are considering using a polygraph test now or in the future, get good legal advice from an employment law attorney in your area. You need to know about federal, state, and local laws before proceeding in this area.

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