The polygraph: police must determine who is telling the truth and who is lying, there is an underlying premise that lying is associated with detectable physiological changes. Two types of questions: crime irrelevant questions. Nothing to do with the crime or behaviour under investigation: crime-relevant questions. Questions that relate directly to the crime at hand. It is believed that suspects guilty of their crimes will have a greater reaction to the relevant questions. Found to have a lot of false positives in this test, it is likely that the crime relevant questions make everyone feel threatened or nervous: comparison question test (cqt) This test also used relevant and irrelevant questions, as well as comparison questions: concerning persons honesty and past history. Guilty people react more to relevant questions, innocent people react more to comparison questions. There is also no way to create standardized questions and they might result in bias in their interpretations of the test results.