Reports of Problems with Polygraph Test

A recent piece of investigative journalism by Marisa Taylor of McClatchy Newspapers has created even more skepticism about the already scientifically-questionable polygraph test. Although polygraph test results are not admissible as evidence in most U.S. courts, the results of a polygraph test play a major role in the police investigation, often times helping the police to obtain confessions and either rule out or target potential suspects. In addition, polygraph exams are frequently used by defense teams, required as part of sex offender treatment and probation programs, and used as part of job application processes.

The article specifically criticizes the LX4000 model which is manufactured by Lafayette Instrument Company, as having a “glitch” that can mean the difference between passing and failing the lie detector. Ten federal agencies, 27 states, including North Carolina, and many local police departments currently use or have relied on the LX4000 to test whether tens of thousands of people are being truthful.

The North Carolina State Bureau of Investigation uses both the LX4000 and LX5000 polygraph models. It is likely that many agencies rely on the LX4000 because the newer model, the LX5000, is more expensive, ranging from $3,200 to $9,500. However, there are still questions that remain unanswered about the accuracy of the newer LX5000 model since the manufacturer, Lafayette, admitted that the new model has the same “potential” as the LX4000 for having troubling issues, according to McClatchy.

The “glitch” identified in the LX4000 relates to the measurement of the amount of perspiration being released by the person taking the polygraph test which is one factor that can indicate his or her level of truthfulness. The LX4000 can measure sweat either in manual mode or automatic mode. The manual mode directly measures the amount of sweat being secreted from the sweat glands. In contrast, automatic mode electronically filters the measurements of sweat, making the data more uniform and easier to interpret. Ideally, the results of the examination would be the same regardless of which mode were used. However, when switching between modes, an alarming 16-point difference has been noted by one veteran federal polygrapher, according to McClatchy. The reason 16 points is such a significant number is that, as Taylor notes, “one point can make a difference” in a polygraph test. Thus, in some circumstances, a person can be classified as a liar or a truth-teller depending on which mode is used.

The results of the LX4000 tend to be less accurate when the automatic mode is used, which is more commonly used by polygraph examiners since it is easier to use and produces more consistent results.

Even more alarming, it is reported that the manufacturing company has been aware of the problem for years. However, the glitch was apparently not shared openly as many polygraph examiners stated in Taylor’s article that they had no idea that their measurements can vary based on which mode they used. Further, since polygraph machines and their operators are not required to pass any certification tests, their potential for inaccurate results are higher than most other forensic equipment which is required to meet certain standards to ensure accuracy.

In response to the attack on its product, Lafayette Instrument Company released a statement two days after Taylor’s article was published. Lafayette assured its customers and colleagues that “there is nothing wrong with the LX4000” and that the LX4000 and LX5000 remain the “best technology available.” Lafayette also maintained that the article was based on “misinformation” and criticized it for alarming people and being misleading. In its response, Lafayette provided a link to the complete set of questions asked by Taylor and the company’s responses. Follow the link to read the correspondence between Taylor and Lafayette manufacturing during Taylor’s investigation in which Lafayette informs Taylor that her information is inaccurate and advises her to verify her sources.

Lafayette maintains that both the manual and automatic modes “have been shown to work satisfactorily.” Lafayette states that no single test item can produce reliable results without analyzing the remainder of the testing data. Perhaps most notably, when posed the question of how often the differences in results occur when manual mode is used instead of automatic mode, Lafayette responds that more research has to be done and it would be “irresponsible to attempt to guess.” However, Lafayette admits that while the results obtained from the two different modes are “in agreement most of the time,” there are “occasional differences,” according to Lafayette’s response.

In sum, attorneys should be aware that there is a potential problem with this particular machine. Many polygraph examiners are aware of this issue and will either use the manual mode of the Lafayette machine or another machine. This problem does not mean that attorneys should discontinue use of private polygraph examinations, but they should discuss this issue with the examiner prior to the exam.


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