Early reports on the accuracy of the polygraph technique were largely anecdotal. For example, if ten suspects were administered a polygraph examination on a particular crime and one of them failed and subsequently confessed, the technique was reported to be 100% accurate. Once proper research methodology was applied, where random polygraph charts of verified truthful and deceptive suspects were blindly scored by a number of trained examiners, the actual accuracy was shown to be in the 90% range.
In the 1970's the academic community started researching the polygraph technique using mock crime paradigms. A typical laboratory study involved instructing half of the subjects to take money from a location in a room and the other half not to take anything from the room. These subjects were then administered a polygraph examination to determine how often the examiner could correctly identify "guilty" or "innocent" subjects. The polygraph technique does not fare well in laboratory studies. Most of these studies report accuracies slightly above chance levels. In fact, there is such a discrepancy between laboratory and field research within the polygraph technique that when conducting meta-analysis or other intra-study comparisons, the findings are always treated separately, with no effort to generalize laboratory results to the field.
Differences between laboratory and field research are not restricted to the polygraph technique. The same pattern emerges when evaluating the behavior symptoms of actual criminal suspects compared to laboratory subjects who participated in a mock crime or other contrived situation. For example, when evaluators are asked to view video-taped interviews of laboratory subjects who have been asked to play the role of a guilty or innocent person, the evaluators are very poor at identifying which subjects are lying and which ones are telling the truth. However, when evaluators are asked to do the same task using video-taped interviews of actual criminal suspects, they achieve accuracy rates far above chance levels.
What is different between subjects in a laboratory setting and actual criminal suspects? The primary difference is the level of motivation the subject experiences at the time of the polygraph examination or interview. In psychology, the construct of motivation is used to describe the determination or drive exerted to accomplish a particular goal. Furthermore, motivation is closely associated with how clearly a goal is defined.
A concept fundamental to all detection of deception techniques is that innocent and guilty subjects form different goals during a polygraph examination or interview. Specifically, innocent suspects form a goal of needing to be believed whereas a guilty suspect's goal is to not be detected in his lie. Consequently, during an interview or polygraph examination an investigator is not really detecting "lies", but rather inferring truth or deception by identifying the subject's underlying goal through behavioral observations.
At this point it may be instructive to return to the motivational differences between subjects in laboratory and field studies. A laboratory subject who is lying about taking $20 from a desk drawer is not facing significant consequences if the investigator detects his lie. During the interview the subject is not concerned that if the investigator detects his lies he will be expelled from college, lose respect or face possible criminal charges. This lack of perceived consequence will cause poor goal development and minimal effort to accomplish that goal. Similarly the innocent laboratory subject who did not take any money is also not concerned that he may be expelled from college, charged with theft or have his reputation ruined if the investigator mistakenly believes that he did take the money. Without significantly different goals, there exist no meaningful difference between the "guilty" and "innocent" subjects attitudes, perceptions or behaviors.
However, consider a group of employees being questioned about the theft of $20 from a co-worker's purse. Each employee is facing probable termination, certain public humiliation and a possible criminal record. Under this high-motivation circumstance, innocent employees are going to form predictable attitudes toward the interview as well as the issue under investigation, e.g., high confidence in being exonerated, forming harsh judgments toward the guilty, and being comfortable speculating about possible suspects and motives for the crime. During an interview innocent suspects will be actively involved in accomplishing their goal of convincing the investigator that they did not steal the missing $20.
Conversely, the guilty suspect who is highly motivated to avoid detection will form quite different attitudes toward the issue under investigation and the interview, e.g., exhibit a lack of confidence in being exonerated, attempt to convince the investigator that no theft occurred, appear uncomfortable and unhelpful in speculating about the crime and express forgiveness toward the guilty person. During his interview, the guilty employee will utilize all of his skills and abilities to accomplish his goal of convincing the investigator that he did not steal the $20.
As this example illustrates, it is not the seriousness of the crime that affects a subject's motivation; the level of motivation experienced by a subject is dictated by the subject's perception of the consequences that will be suffered if it is determined (correctly or incorrectly) that he engaged in the crime. A subject's level of motivation is not only important when evaluating published research but also when considering a subject's behavior in field situations. The following circumstances each involve situations in which a subject may experience decreased motivation, and therefore offer misleading behavior symptoms during an interview:
Interviewing Subjects Facing Minimal Consequence
Some juveniles have had so much contact with the criminal justice system that they know that the worse consequence facing them is a short stay in a juvenile home. Similarly, a recently hired employee who engages in dishonesty knows that he has little to lose if the investigator detects his deception. Under both of these circumstances guilty subjects may not form attitudes typical of a deceptive person. This is especially true when the subject has a low level of social consciousness and perceives minor punishments as a mark of honor among peers.
Fortunately, during these investigations factual analysis often points toward the probable involvement of the guilty person. A detection of deception guideline that has proven valuable in many investigations is to not allow apparent truthful behavior symptoms to out-weigh deceptive factual analysis. When investigative information points toward a particular suspect, in most situations that person should be interrogated regardless of apparent truthful behavior.
Interviewing Subjects Who Feel Immune From Consequences
There are some subjects who believe, because of their position or social influence, that they can escape consequences for acts of wrong-doing. Examples include prominent businessmen, powerful politicians, judges, high-ranking military or law enforcement personnel. Individuals who fit this description often display a feeling of entitlement as if they are "above the law."
In one-on-one allegations sometimes the accused has much more authority and credibility than the victim. Examples of this circumstance includes a teacher accused of sexual conduct with a mentally retarded student or a police office accused of extorting sexual favors from a prostitute. Under this circumstance the guilty suspect may be quite confident that others will accept his word over that of the victim's.
When interviewing a suspect who may fall into this category, it is beneficial to emphasize the objectivity of the investigation and analysis of evidence. In essence, the investigator is telling the suspect that neither of them can control the outcome of the investigation. In addition, it is recommended to start the interview with a statement similar to the following, "George, if you did solicit sex from that woman our investigation will clearly indicate that. On the other hand, if you did nothing wrong we will be able to prove that as well."
Interviewing a Guilty Subject Early During an Investigation
It is not uncommon for a guilty subject to be questioned early during an investigation and escape detection. Presumably, these subjects approach the questioning as "routine" and do not experience significant fear of detection during the interview. After incriminating evidence is developed and the subject is interviewed a second time, the heightened level of motivation causes the suspect to exhibit attitudes and behavior symptoms typical of a guilty person.
Just as it is always a good practice to re-interview traumatized victims or witnesses a couple of days after the initial report, it is often prudent to conduct a second interview of initial subjects even if there were no apparent behavior symptoms of deception during the first interview. The mere fact that the subject is being questioned a second time will heighten the motivation level of both innocent and guilty subjects, causing their behavior to be more definitive and reliable.
Interviewing Subjects With Low Intelligence
To appreciate the possible consequences associated with success or failure of accomplishing a goal involves assessment, comprehension, judgment and knowledge, e.g., intelligence. A suspect with a lower intelligence may understand the difference between lying and telling the truth, but not fully grasp the concept of going to jail, losing respect and trust or the financial significance of paying a substantial forfeiture. Investigators should always be cautious in drawing inferences based on behavior symptoms exhibited by subjects with low intelligence.
Approaching A Subject As If He Is Innocent
An innocent subject will not form predictable attitudes and perceptions if he is not concerned that the investigator might believe he is involved in the crime. Clearly, it would be improper for the investigator to start an interview in the following manner, "Mike, as you probably know there was a fire in your neighbor's garage over the weekend. I certainly don't think that you had anything to do with starting it, but I still need to ask you a few questions about it. Would that be alright with you?"
The innocent suspect must experience the need to convince the investigator that he did not commit the crime. Only when the innocent suspect understands that the most effective way to be exonerated is to help the investigator solve the crime, does he manifest predictable attitudes and perceptions e.g., offers cooperation, discusses possible suspects, eliminates possible suspects, makes admissions against self-interest, forms harsh judgments toward guilty, etc.
A fundamental principal of detection of deception theory is that there should be no difference between the interview of a suspect who is more likely innocent or guilty of a crime. Both suspects must form a specific goal during the interview and be motivated to accomplish that goal. The following introduction satisfies this requirement: "Mike, as you know there was a fire in your neighbor's garage over the weekend and I am interviewing people who were in the area of the fire. Some of the questions I'll be asking you I already know the answer to. The most important thing is that you be completely truthful with me before you leave today. Before we go any further, let me ask, did you start that fire?"
Interviewing Suspects Who Have Given Up
An interesting phenomenon within the polygraph technique is that if a subject becomes convinced that the test is infallible, there is a risk that the subject will become emotionally unresponsive. The entire premise of the control question polygraph technique is built upon the subject directing psychological attention toward a particular question type (control question for truthful, relevant question for deceptive). The focus of the subject's attention is identified through physiological changes resulting from the subject's fear that he will show a "lie response" to that question. On the other hand, if the subject believes that the polygraph will most certainly indicate that he is lying the subject will simply answer the test questions and not experience a significant emotional response; for the polygraph technique to function as designed, the deceptive subject must have some hope that he can get through the examination without being detected and the truthful subject must have some fear that the results may indicate that he was involved in the crime. Psychologically, both the innocent and guilty subjects must believe they have some control over the outcome of the examination.
The same is true during an interview. This is one of the reasons an investigator should not become accusatory during an interview or overwhelm a subject with incriminating evidence early during an interview. A guilty subject who perceives that the investigator is already convinced that he committed the crime may simply withdraw and not form attitudes or perceptions typical of a guilty person. For similar reasons, a subject who is questioned shortly after committing a crime and is knee-deep in incriminating evidence may not form attitudes typical of other guilty suspects who, during the interview, perceive a possibility of getting away with their crime if they are convincing enough.
In conclusion, there is no such thing as a lie detector. When people lie or tell the truth they do not produce some identifiable pattern on a polygraph chart nor do they engage in any unique observable behaviors. Rather, detection of deception techniques have been developed to infer truth or deception based on identifying the different goals that guilty and innocent people tend to form when questioned about an act of wrong-doing. However, it is not engaging in the act of wrong-doing that causes the goals to form. It is the perceived consequence associated with the act that causes the innocent person to be strongly driven to want people to know that he did not commit the act or the guilty person to do everything in his power to try to convince people that he did not commit the act., e.g., motivation. The effects of motivation are not only important when reviewing research studies but also during field interviews. Just because an investigator is interviewing an actual criminal suspect does not necessarily mean that the suspect is operating from a high-motivation perspective.