Some Avoidable Lie-Detector Mistakes

Article excerpt

The most competent lie-detector examiner ma), and does make mistakes, and in a certain percentage of his cases he is unable to arrive at a definite opinion as to whether his subject is telling the truth or lying. Nevertheless, many lie-detector errors and inconclusive test results are avoidable ones. The factors which generally account for this latter group may be briefly stated as "unfit subjects" and "unqualified examiners."


Most lie-detector errors and inconclusive test results are attributable to the incompetency of the examiner conducting the test. In many instances, however, they are properly chargeable to a prevailing practice whereby otherwise qualified examiners will accept for test purposes subjects who have been rendered unfit for any such testing because of the treatment they have encountered at the hands of police investigators before being presented for lie-detector tests.

No one in his right mind would expect a medical technician to conduct a satisfactory metabolism test on a patient who had just emerged from a fist fight or who had been chased up a flight of stairs or who had been verbally abused and threatened while on his way to the examination room. Yet the thought apparently seldom occurs to some police investigators that a person may be rendered unfit for a lie-detector test by an extensive interrogation based upon frequent and constant accusations of guilt. In many of these instances, the lie-detector examiner is unable to make a diagnosis that he considers reliable; his report is "indefinite" or "inconclusive," and so the press report reads too. In cases where the extensive interrogation is accompanied by actual physical abuse, the positive suggestions of guilt constituting part of the "third degree" procedure may produce test reactions which will simulate true deception criteria in an innocent person's record. There is at least one such case in which this actually happened. The same pre-test experience also may so condition a guilty subject that his enmity toward the investigators becomes the center of his thinking rather than the offense itself, and the ordeal may actually relieve him of whatever mental conflicts are present because of his criminal act. In this event it is highly probable that a "third degree" victim's deception may not be detected by the lie-detector technique, and another lie-detector failure will probably find its way into the press reports.

Any testing which is attempted under the conditions just described is unfair to the lie-detector technique and to the examiner as well.

Experience on the part of competent examiners who restrict their practice largely to personnel investigations indicates that their percentage of accuracy and of definite reports far exceeds that of examiners in police cases. The difference may be attributed in large part to the fact that the personnel investigator's subjects are in much better condition for their tests. They have not been physically abused or extensively interrogated.

What can the police-employed lie-detector examiner do to remedy the present situation? Three things:

1. Establish a practice of refusing to test a subject who has been physically abused.

2. Where the circumstances are in the extreme, refuse to examine a subject who has been extensively interrogated, even though no direct physical abuse has been administered.

3. Try to develop a procedure within the particular police department whereby lie-detector tests will ordinarily be conducted during the early stages of an investigation or interrogation rather than as a last resort when all else has failed.

To some persons these suggestions may appear to be naively conceived. They will say that only a very unrealistic individual will expect a lie-detector examiner who is working in or for a police department to adopt such an attitude and survive the consequences. …