considers to be untrue. Although it is hard to think of
a context in which nodeception transpires, the study
of deception and how to detect it is especially crucial
in the forensic setting. Most law enforcement profes-
sionals, who must assess veracity on a daily basis,
know that deception is quite frequent in forensic con-
texts and that making mistakes when assessing verac-
ity can have severe consequences—the innocent may
be sentenced to punishment, the guilty may be freed
to commit more crimes. To be able to correctly detect
deception is therefore of utmost importance. Yet com-
prehensive study over the past 40 years has shown that
the human ability to detect deception is just above the
level of chance. The consistency of this finding is
striking, although there are factors moderating the rate
of correct judgments. For example, accuracy is some-
what higher when listening to rather than watching the
liar, when one has access to baseline information
about the liar’s behavior, and when detecting unpre-
pared rather than prepared messages.How to Study Deception Detection
To gain insight into deception, psychologists and
other researchers conduct experiments. They instruct
some people either to lie or to tell the truth and
instruct others to judge the veracity of the resulting
statements. Those who lie or tell the truth in these
experiments are referred to as senders, the truthful and
deceptive statements as messages, and those who
judge the messages as receivers.In this entry, the
accuracy of these receivers is at focus, more specifi-
cally the accuracy of human judgments made without
any specialized tools or aids in detecting deception on
the basis of verbal content and the liar’s behavior. The
receivers are typically given videotaped or audiotaped
statements, and ordinarily, half the messages a
receiver encounters are truths and half are lies; hence,
the chance level of correct judgments a receiver could
expect is 50%. Lie detection ability is most often
expressed as percent correct, but other indices of
deception detection accuracy, such as standardized
differences between truth and lie detection accuracy,
are also calculated.
The standard lie detection experiment contains sev-
eral factors that have been examined through experi-
mental manipulation. For example, the senders of the
message can be adults, adolescents, or children, or
they can be persons with or without special skills at
lying, such as experienced criminals. Furthermore, thecontent of the lies (and truths) have been varied:
People have lied about their personal feelings, about
their committing of transgressions such as adultery or
sanctioned crimes, or in placing the blame on some-
one other than the culprit. Lie detection through dif-
ferent media has also been tested: Are people better lie
detectors when having access to video or audio or
written transcripts? In addition, characteristics of the
receivers have been varied: Are certain groups of
people, such as police officers, better lie detectors?
These are only some of the factors that have been sci-
entifically examined.Overall Results
Overall accuracy of lie detection has been analyzed in
several meta-analyses and reviews. The results are
unanimous in terms of the mean percentage of accu-
racy: In the typical research setting, lies are discrimi-
nated from truths at levels that are only slightly better
than would be attained by flipping a coin. The mean
percentage of accuracy is just under 54. This effect is
small, but since it is based on thousands of veracity
judgments, it is significantly better than the level of
chance. Typically, studies report an accuracy rate
between 50% and 60%.
In calculating the just presented overall percentage
of accuracy, some exclusion criteria have been
applied. Studies in which training to detect deception
is provided are not included, nor are studies on adults’
ability to detect children’s deception. Also excluded
are studies on implicit lie detection and studies not in
the English language.
Because deception judgments can have severe con-
sequences whether or not they are correct, it is impor-
tant to understand the factors that may bias the
judgments in one direction or another. The research
literature has evidenced a truth bias—receivers’ ten-
dency to make systematic mistakes in the direction of
judging messages as truthful, with a mean percentage
of around 56% (which is significantly greater than
50%). One consequence of this truth bias is that
people on average correctly identify truthful messages
(mean percent correct just above 61%) more often
than they correctly identify deceptive messages (mean
percent correct just below 48%).
Using percent correct as a measure of accuracy has
been criticized, and other measures have been sug-
gested. However, analyses of log-odds ratios or signal
detection measures, among others, also indicate an208 ———Detection of Deception in AdultsD-Cutler (Encyc)-45463.qxd 11/18/2007 12:41 PM Page 208