A polygraph, popularly referred to as a lie detector, measures and records several physiological indices such as blood pressure, pulse, respiration, and skin conductivity while a person is asked and answers a series of questions.

The belief underpinning the use of the polygraph is that deceptive answers will produce physiological responses that can be differentiated from those associated with non-deceptive answers.

There are, however, no specific physiological reactions associated with lying, making it difficult to identify factors that separate liars from truth tellers.

Polygraph examiners also prefer to use their own individual scoring method, as opposed to computerized techniques, as they may more easily defend their own evaluations.

A statistical hypothesis, sometimes called confirmatory data analysis, is a hypothesis that is testable on the basis of observing a process that is modeled via a set of random variables.

A statistical hypothesis test is a method of statistical inference.

Commonly, two statistical data sets are compared, or a data set obtained by sampling is compared against a synthetic data set from an idealized model.

A hypothesis is proposed for the statistical relationship between the two data sets, and this is compared as an alternative to an idealized null hypothesis that proposes no relationship between two data sets.

The comparison is deemed statistically significant if the relationship between the data sets would be an unlikely realization of the null hypothesis according to a threshold probability—the significance level.

Hypothesis tests are used in determining what outcomes of a study would lead to a rejection of the null hypothesis for a pre-specified level of significance.

The process of distinguishing between the null hypothesis and the alternative hypothesis is aided by identifying two conceptual types of errors, type 1 and type 2, and by specifying parametric limits on e.g. how much type 1 error will be permitted.

Lie detection is an assessment of a verbal statement with the goal to reveal a possible intentional deceit.

Lie detection may refer to a cognitive process of detecting deception by evaluating message content as well as non-verbal cues.

It also may refer to questioning techniques used along with technology that record physiological functions to ascertain truth and falsehood in response.

The latter is commonly used by law enforcement in the United States, but rarely in other countries because it is based on pseudoscience.

There are a wide variety of technologies available for this purpose.

The most common and long used measure is the polygraph, which the U.S. National Academy of Sciences states, in populations untrained in countermeasures, can discriminate lying from truth telling at rates above chance, though below perfection.

They added that the results apply only to specific events and not to screening, where it is assumed that the polygraph works less well.