Validity is the same as Accuracy. Reliability
is the ability of a second examiner, without the benefit of case facts or
the interview, to revisit the charts to come up with a concurring diagnosis;
just a blind study of the charts.
The American Polygraph
Association has a compendium of research studies available on the validity
and reliability of polygraph testing. The 80 research projects listed, published
since 180 involved 6,380 polygraph examinations or sets of charts from examinations.
Researchers conducted 12 studies of the validity of field examinations,
following 2,174 field examinations providing an average accuracy of 98%.
Researchers conducted 11 studies involving the reliability of independent
analyses of 1,609 sets of charts from field examinations confirmed by evidence,
providing an average accuracy of 92%. Researchers conducted 41 studies involving
the accuracy of 1,787 laboratory simulations of polygraph examinations, producing
an average accuracy of 80%. Researchers conducted 16 studies involving the
reliability of independent analyses of 810 sets of charts from laboratory
simulations producing an average accuracy of 80%. Tables list the authors
and years of the research projects, which are identified fully in the References
Cited Surveys and novel methods of testing are also mentioned.
Why do critics figures vary?
One of the problems in discussing accuracy figures and the differences between the statistics quoted by proponents and opponents of the polygraph technique is the way that the figures are calculated. At the risk of over simplification, critics, who often don’t understand polygraph testing classify inconclusive test results as errors. In the real life setting an inconclusive result simply means that the examiner is unable to render a definite diagnosis. In such cases a second examination is usually conducted at a later date.
To illustrate how the inclusion of inconclusive test results
can distort accuracy figures consider the following example: If 10 polygraph
examinations are administered and the examiner is correct in 7 decisions,
wrong in 1 and has 2 inconclusive test results, we calculate the accuracy
rate as 87.5% (8 definitive results, 7 of which were correct.) Critics of
the polygraph technique would calculate the accuracy rate in this example
as 70%, (10 examinations with 7 correct decisions.) Since those who use polygraph
testing do not consider inconclusive test results as negative, and do not
hold them against the examinee, to consider them as errors is clearly misleading
and certainly skews figures.
An Examiner’s education and experience are important factors.