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Polygraph Exams and Pre Employment Screening in Law Enforcement

How Lie Detector Tests Work and Why You Shouldn't Be Nervous About Them

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Person's hand hooked up to polygraph test, close-up (Overhead view)
Seth Joel / The Image Bank / Getty Images
For most people looking to land a job in law enforcement professions, the chances are high that a polygraph exam is in their future. Understandably, the so-called "lie detector" test is a huge source of anxiety for so many aspiring police officers, FBI agents and other criminal justice career hopefuls during the employment background investigation.

Fortunately, the polygraph doesn't have to be a stressful experience. Learning about the exam and how it works can help you feel better about your prospects of passing and help get you one step closer to the perfect criminal justice job for you.

Invention of the Lie Detector

The polygraph was developed by John Larson, a police officer and medical student in Berkley, California, and has been in use now for nearly 100 years. Larson believed that when people lied, they would experience slight, involuntary physiological changes. If he could detect and record those changes, he could catch the lie.

The instrument measures multiple vital signs to indicated whether or not someone is being deceptive. The polygraph examiner looks for changes in blood pressure, heart rate and respiration to identify deception.

The Polygraph Process

For the law enforcement job applicant, the polygraph exam is probably the most nerve-wracking step in the hiring process.

Pre Test

The preemployment examination typically starts with a pre exam questionnaire. The questionnaire is similar to the supplemental application that most agencies require candidates to complete prior to screening. The pre exam, though, is often far more in-depth.

The questions are broken up into sections, and the applicant provides written answers in the book. Generally, it will take a new candidate up to two hours to complete the booklet. For prior law enforcement or corrections officers and military personnel, it may take even longer due to more relevant questions about their past employment.

Applicants can expect to answer questions about past drug use, criminal behavior and employment history. They may also be asked to disclose information about the frequency and quantity of their use of alcohol, as well as other issues that, while not illegal, may indicate personality traits or habits that are less than desirable in police employment.

Taking the Lie Detector

After completing the questionnaire, the actual polygraph exam will begin. The applicant dons a blood pressure cuff and other devices that are connected to the testing instrument. The examiner will get a baseline reading of vital signs.

The examiner will then ask a series of yes or no questions that are already known to be true. For example, if the applicant's name is Robert, the examiner would ask "Is your name Robert," to which Robert would answer yes. Similarly, the applicant will be asked other yes or no questions about already known information and will be instructed to purposefully lie. In this way, the examiner can establish a record with which he or she can compare the results of the actual test.

After establishing the baseline and control questions, the actual exam begins.  Surprisingly, this usually takes the least amount of time. The applicant will be asked a series of yes or no questions based on the answers he gave in the pre exam questionnaire.

Detecting Deception

The purpose of the employment polygraph test is, of course, simply to determine whether or not a candidate is being truthful on his or her job application. Any indication of deception may be cause for disqualification from consideration for employment.

Answers from the pre exam questionnaire may also indicate background disquallifiers, especially if they show previously undetected serious crimes or if the answers are different than those given on the supplemental application.

Do Polygraph Tests Work?

A lot of skepticism surrounds the validity of polygraphs, but the fact remains that they are an effective tool in screening applicants for criminal justice jobs. Regardless of whether or not the instrument can reliably detect deception, it cannot be ignored that the tactic can often elicit truthful responses from people who may otherwise be inclined to lie during their background investigation. So long as people believe there is a better-than-average chance of being found out, they will more often than not tell the truth.

To Catch a Predator...

In fact, employment polygraphs have been instrumental in discovering a host of serious crimes that may have otherwise gone undetected. Many of those crimes, including major felonies and serious misdemeanors, have been successfully prosecuted due to the applicants' own admissions, recorded in their pre exam booklet.

Can You Beat the Polygraph?

So can you beat a polygraph test? If you're applying for a career in criminal justice, perhaps the better question is, should you try to beat the lie detector test. Remember, law enforcement professionals necessarily hold positions of great trust in their communities. If you're someone who is inclined to want to circumvent polygraph screening, perhaps a criminal justice career isn't for you.

With that being said, the principle of the test requires that the subject knows they are lying and that they care that they are being deceptive. There are members of the population for whom lying has no bearing on their conscience and, therefore, will be less likely to show the types of physiological responses the instrument is designed to measure.

Nervous About the Lie Detector

For people who have a nervous disposition or a guilty conscience, though, there's no need to fear. The purpose of the initial control questions is to establish the individual's normal range. Since the test looks for changes in physiology, your overall demeanor won't have any bearing on the exam; instead, how you feel about each individual question asked will register as either a truthful, deceptive or inconclusive response.

Relieving the Anxiety

Employment polygraph testing has become a valuable tool in pre employment screening, at least for criminal justice professionals and agencies. Understandably, though, there remains a tremendous amount of anxiety and fear of the unknown regarding the exam. While a better understanding of how the lie detector test works can go a long way toward alleviating stress, the simple fact remains that there's nothing to do but take it if you truly want the job.

If you're nervous about your upcoming polygraph, remember a few key things:

  • First of all, the past is the past. You can't change it; all you can do is let the chips fall where they may.
  • Second, if you are truly interested in working as a law enforcement officer, you should have nothing to hide and everything to gain from the test.
  • Finally, and most importantly, honesty is one of the most respected and highly valued virtues within the criminal justice community.

Honesty is Always the Best Policy

While some minor past indiscretions can be forgiven, you don't want to start a new career on a dishonest note, and most departments will punish lying faster than any other infraction. As Aesop said, honesty is always the best policy, especially when it comes to lie detection and the employment process.

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