Public Opinion About the Polygraph

The public is routinely informed that suspects have been administered a polygraph test and have either failed or passed the test. In some cases, this information is provided during the trial. Consequently, how the public judges the polygraph test is of interest to those in the legal community. A number of studies have addressed how the public responds to polygraph tests, and these studies generally suggest that people react to polygraph test results much differently than the courts assume they do.

As used in criminal investigations, the polygraph test consists of a series of questions administered to a suspect by a polygraph examiner, who measures the suspect's physiological responses to each of the questions. In most instances, the pattern of questioning of suspects involves a variant of the Control Question Test (CQT), in which suspects are asked both relevant questions and control questions. A pattern of higher physiological responses to the relevant questions results in a failed test.

The courts have been largely unwilling to admit polygraph test evidence into trials. Much of this reluctance stems from the concern that the polygraph test cannot reliably determine when someone is truthful or deceptive. This concern was first articulated in 1923 in Frye v. United States, in which it was ruled that the lie detector had not gained general acceptance in the scientific community. Today, courts routinely cite the 1993 case of Daubert v. Merrell Dow Pharmaceuticals, which did not concern the polygraph specifically but rather any scientific evidence. More important to the present discussion, a second concern surrounding the polygraph test is that the public may see the test as infallible and place unwarranted trust in the results. Because the polygraph test gets directly to the heart of the matter—whether the suspect is truthful or deceptive in denying the crime, there is the fear that jurors will simply disregard all other evidence and place their trust entirely in the results of the polygraph test. This belief on the part of the court was articulated in the 1975 case of United States v. Alexander.

Polygraph test results typically are entered into trial evidence either as a result of prior stipulation (i.e., prior agreement between the parties) or as a result of a separate hearing. Presently, approximately one third of the states allow polygraph tests into evidence under prior stipulation. Stipulated tests arise in instances where the prosecutor asks a defendant to submit to a polygraph test and agrees to drop the charges if the test is passed but will introduce the test results into evidence if the test is failed. In instances where the defense wants to admit the results of a passed test over the objection of the prosecution, a hearing typically called a Kelly-Frye or a Daubert hearing is conducted to determine the admissibility of the polygraph evidence.

Several studies have investigated whether jurors are likely to place unwarranted trust in polygraph test results. Here, the findings have been consistent in showing that the public remains rather skeptical about the validity of polygraph tests. These findings have come about from jury simulation studies, in which the participants are given information about a criminal trial and asked to render judgments. The cases in these studies have varied the crime in question from burglary to rape to murder. The manner in which the trial information was presented to participants has varied from videotaped trial simulations, audiotaped information, and lengthy trial transcripts, to brief summaries of trial facts. Moreover, the characteristics of participants have also varied, from college undergraduates to samples of community members.

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