6.4.ll Polygraphs used in criminal investigations typically measure five bodily functions: (1) thoracic respiration, (2) abdominal respiration, (3) blood pressure and pulse rate, (4) muscular movement and pressure, and (5) galvanic skin response. In principle, the magnitude of these responses when the subject is asked a relevant question ("Did you murder your wi£er) indicate whether he is lying or telling the truth. The procedure, of course, is not infallible, as a .recent study bore out (80). Seven experienced polygraph examiners were given a set of 40 records--20 were from innocent suspects and 20 from guilty suspects. The subjeds had been asked 11 questions, on the basis of which each examiner was to make an overall judgment: "Innocent" or "Guilty." The results are as follows:
Examiner's "Innocent" Decision "Guilty"
What would be the numerical values of ct and f3 in this context? In a judicial setting, should Type I and Type II errors carry equal weight? Explain.
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