Concealed Information Test

How the Test Works

For example, say it is 8:00 a.m. and a man is having breakfast when he hears someone knocking on his door. He opens the front door and sees two police officers. They tell him that there has been a fire at his former partner's place. He is accused of arson, and the police invite him to take a concealed information test to find out whether he knows more about the fire. The police ask if he has any idea where the fire started and what kind of material was used.

The police connect him to a polygraph in order to measure skin conductance, breathing, and heart rate. Then the concealed information test starts. The police ask, “Do you know where the fire started? Was that in the kitchen? In the garage? In the cellar? In the porch? In the hallway?”

He answers “no” to each of the options. Then, he is questioned about the kind of material that was used to start the fire. After a few questions, the test is over.

While he gets the chance to sip his coffee, the police examiner takes a few minutes to analyze the test results. As all alternatives are equally plausible, a key assumption of the concealed information test is that the innocent examinee will show similar physiological responses to all alternatives. Because the man is stressed out, his heart rate may be abnormally high but it will not be particularly higher or lower while truthfully denying recognition.

[Page 191]This situation is quite different for the guilty examinee. If the man did start a fire at his former partner's porch using paint thinner, the concealed information test expects him to recognize these crime details and show a marked physiological response to it.

Studies on the Test

Since its introduction at the end of the 1950s, there have been hundreds of studies on the concealed information test, examining whether it works, under which conditions it works, and why it works. The majority of these studies were conducted in university laboratories. Here, researchers make sure some study participants have specific knowledge of a crime. Participants may be asked to select one of five playing cards, allowing the researcher to develop concealed information test questions such as “Did you select the Queen of Hearts? The King of Spades?”

Other options are to ask for autobiographical information, such as participants' birth date, or to have participants learn a list of words and ask them to conceal word recognition for the experimenter. The great advantage of such laboratory studies is that the researcher knows for sure who knows what (ground truth). A disadvantage is that the stakes are low, and that the set up and questions differ greatly from those of real-life criminal investigations. The most realistic laboratory set up is the mock crime design. Here, some participants enact a crime (e.g., the theft of $20), whereas others have nothing to do with the crime. Promising participants that they will get an extra $20 if the concealed information test considers them innocent is one technique that has been used to raise the stakes.

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