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.
In these studies, when evidence that the defendant failed a polygraph test is introduced into the trial, it consistently has failed to affect verdicts or measures related to verdicts (e.g., confidence ratings, strength of evidence ratings). In comparison, in studies in which other forms of equally suspect evidence are also introduced—such as eyewitness testimony, participants have tended to rely heavily on this information when rendering judgments. Moreover, participants fail to draw a distinction among the different types of polygraph test evidence. For example, research has consistently shown that the Guilty Knowledge Test (GKT) is much less likely to result in false positives (i.e., truthful suspects misclassified as deceptive) than is the CQT. Yet when studies have varied the type of polygraph test admitted in instances where the defendant failed the test, again no differences were found. That is, participants are no more trusting of the GKT than they are of the CQT. When researchers have varied whether the polygraph test results indicated that the defendant had passed the test or failed the test, there were again no differences in verdicts when compared with a control group that did not receive polygraph test results in the trial. Finally, because it is possible that participants are less apt to rely on polygraph evidence when other, more reliable forms of evidence are present than when it is the sole evidence against the defendant, researchers have varied the presence of failed polygraph evidence both with and without other corroborating evidence. Again, no differences were found for guilty judgments, as participants were no more likely to rely on polygraph evidence when it was the chief evidence against a defendant than when it was one of many pieces of evidence against the defendant.
However, whereas jurors are rather reluctant to use polygraph evidence in their decisions, the general public appears to be less skeptical of the test than are experts. That is, surveys of experts in areas such as psychophysiology suggest that compared with the general public, they are more uniformly condemning of the value of polygraph tests. The general public tends to be more varied in its beliefs. Moreover, the general public is less inclined to perceive subtle differences in the techniques (e.g., CQT vs. GKT) but rather holds a generally skeptical attitude toward all polygraph tests. What is clear, then, is that despite the opinions of many within the legal community who fear that polygraph evidence may be overly probative in the minds of jurors, the research thus far is consistent in demonstrating that neither are polygraph test results highly valued by jurors nor do jurors place unwarranted trust in the test when rendering judgments concerning the defendant.
- Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993).
- Frye v. United States, 293 F. 1013 (D.C. Cir. 1923).
- Lykken, D. T. (1998). A tremor in the blood: Uses and abuses of the lie detector (2nd ed.). New York: Plenum Press.
- Myers, B., Latter, R., & Abdollahi-Arena, M. K. (2006). The court of public opinion: Lay perceptions of polygraph tests. Law and Human Behavior, 30(4), 509-523.
- United States v. Alexander, 526 F.2d 161, 164 (8th Cir. 1975).
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