In theory, if a subject lies on an important question, his polygraph response will be different from the truthful responses to the neutral questions. Does this really work? It’s true that a polygraph can measure emotional stress, and it’s also true that MOST people have greater emotional stress when they lie. Unfortunately, many people are likely to have an emotional response to the important question, whether they lie or not. After all, “Did you kill your wife?” is more emotionally charged than “What’s your name?” This effect is so great, one study has shown that you’ve got a fifty-fifty chance of failing a polygraph test, even if you’re innocent! Because of these odds, lie detector tests are not allowed as evidence in court cases.