Group one of the National Congress on Judicial Reform preparatory committee passed a resolution that would prohibit performing polygraph tests — commonly known as lie detector tests — on the disadvantaged, in the hope of protecting the rights of disadvantaged victims and defendants in lawsuits.
However, defining “disadvantaged” is problematic. Another issue to consider is whether a polygraph test would be more or less effective depending on whether the subject belongs to a privileged or a disadvantaged group.
The premise for polygraph testing is that the truth or falsehood of one’s statement will trigger a specific, uncontrollable, physiological reaction in the subject that can be measured and then interpreted by an expert. These assumptions may appear scientific, but they have always been controversial.
The doubts about performing polygraph tests mainly focus on their objectiveness: Whether the examiner is an expert, whether the polygraph instrument meets standards, whether the environment where the test is performed is normal; all these factors will affect the results of a test, and in combination with the fact that physiological conditions differ between people, the question is how there could be a consistent benchmark for evaluation.
Other scientific tests, such as DNA tests, are not affected by such factors, and such tests can be reproduced by other experts using the same procedure, which means that their accuracy is extremely high.
In comparison, polygraph testing cannot rule out many of the variables, which means that it does not have the reproducibility required by science, and the accuracy of the process and the results cannot be examined — a fatal weakness of polygraph testing.
Although practical criminal justice in Taiwan does not rule out this method of evidence, it does require that the examiner has received expert training and is experienced, that the equipment is of good quality and operates normally and that the environment does not interfere.
In addition, polygraph tests require that the subject is in a normal physical mental state. In order to keep the respondent in this state, examiners must inform the subject of their right to refuse the test and the possible effects of polygraph testing, and they must verify that the subject’s physical and mental state is conducive to conducting a test.
That there are so many requirements reveals the concern that a lie detector test carried out under duress will violate the defendant’s right to a defense and that results are likely to be distorted.
Although judicial practice has such strict requirements around polygraph testing, in reality these requirements might not be met, because the environment is controlled by the interrogator and the subject is alone. Even if the subjects are innocent, it is doubtful whether they would be in their normal physical and mental state.
Furthermore, there is no institution to issue expert certificates to interrogators and no objective standard for procedures, which raises the question of how polygraph results should be validated.
Even worse, polygraph testing is often carried out because prosecutors think defendants are not telling the truth. This creates a risk that examiners might be prejudiced and makes it difficult to ensure that they are truly objective. Even if the defendant does not confess, these factors would make it hard not to fail the test, in effect turning it into a confession.
It often happens that even if the subject passes the polygraph test, the authorities reject the result and send the defendant to another institution for another test. This not only seriously violates the defendant’s right against self-incrimination, it also raises suspicions that defendants are given polygraph tests over and over again to frame them.
The validity of the polygraph test in criminal trials therefore has nothing to do with whether the subject belongs to an advantaged or disadvantaged group. However, it is necessary to comprehensively review whether this technology is a matter of pseudoscience disguised as science and whether it should be banned from the courtroom.
After all, the mindset that if a defendant does not confess, they will be subjected to a polygraph test — and if they do not pass the test, they are guilty — violates the presumption of innocence and is possibly a source of injustice.
Wu Ching-chin is chair of Aletheia University’s law department.
Translated by Lin Lee-kai
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