Paul Ekman published a study in 1991 in which much was learned about lying and people's accuracy when detecting lies. In the study, participants were shown video clips of people talking and were asked to judge whether or not the people were lying in the video clip. Ekman tested certain groups of people including the Secret service, federal polygraphers, robbery investigators, judges, psychiatrists, and college students.
The results indicated that the only group that performed significantly better than the rest at detecting lies was the Secret Service. Ekman's explanation of this was that the Secret Service spends a lot of time scanning crowds and reading body language. Paying attention to non-verbal cues is very important in detecting lies.
Liars tend to show nervous behavior such as crossing their arms, tapping their fingers, and leaning back in their chairs while they are fibbing. They also tend to speak in a slightly higher tone while lying. Shifty eyes may also be indicative of a lie.
Better lie detectors rely on both verbal and non-verbal cues and are better able to detect subtle facial expressions. It was also found that neither gender out-performed the other in the study.