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5. So-called accuracy rates for the polygraph machine vary wildly. It appears that in polygraph testing, laboratory results are inferior in accuracy to field tests. This is, of course, the reverse of usual scientific experience. There are a myriad of other problems of statistical defences and claims (for an excellent explanation of these problems see Lykken's A Tremor in the Blood, pp 63-82).
In citing accuracy levels, much is made of reliability and validity. The former describes the degree to which various polygraph results corroborate one another; the latter characterizes the ability of the polygraph to actually detect falsehood. As one would expect, the reliability of the test is better than the validity because testers tend to have prior knowledge of test outcome and wish to verify each other. The validity of the procedure ranges from no better than chance for exonerating an innocent person, up to 80 percent for detecting a guilty, or at least apparently deceptive, person in a given setting.
While there are many claims of very high accuracy levels, up to 99 percent, Morand and polygraph researchers such as Lykken could find no evidence to substantiate such high accuracy levels for detecting either guilty or innocent persons. Morand was at pains to point out that "decisions based on physiological data alone were no better than chance" (Morand Report, pp 237), and that any higher level of detection came from psychological observation by testers and by using prior information about the subject.
While in some cases test results show better results than chance, certainly any procedure that involves a relatively intelligent person questioning a subject about his actions over a protracted period would result in a degree of effective detection; in fact, that is what the court system or job interview does in any case, perhaps even more effectively than the polygraph-and without the danger of false accusation in a test that is presented as scientifically based and is therefore given undue credence.
6. The evidence that the polygraph machine transmits to paper is at best ambiguous. The polygraph device itself, which has essentially been unchanged since the 1930s, transmits physical evidence that is subject to many physiological idiosyncracies of the subject and test environment.
The measurements themselves are aprocryphal: the blood pressure monitor in the cardio channel is both crude and inaccurate as a measure of blood flow or heart activity. Morand expresses severe reservations about what the measurement itself is:
The channel measures some complex physiological resultant in the cardiovascular activity, consisting of a mixture from blood pressure, heart rate, pulse volume, blood flow to the muscles and flow to the skin, and is then displayed in a relatively crude but very graphic manner (Morand Report, pp 241).
While the GSR channel, used with modern, sensitive equipment and in the hands of well trained personnel, may be a useful indicator of origins of stress, scientists who are proponents of this avenue of channel research concede that GSR testing is very limited in its use, and certainly not useful to identify the source of such stress.
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