10. Lie detectors are controversial instruments, barred from use as evidence in
ID: 3246932 • Letter: 1
Question
10. Lie detectors are controversial instruments, barred from use as evidence in many courts. Nonetheless, many employers use lie detector screening as part of their hiring process in the hope that they can avoid hiring people who might be dishonest. There has been some research but no agreement, about the reliability of polygraph tests. Based on this research, suppose that a polygraph can detect 65% of lies, but incorrectly identifies 15% of true statements as lies. A certain company believes that 95% of its job applicants are trustworthy. The company gives everyone a polygraph test asking, “Have you ever stole anything from your workplace?” Naturally, all the applicants will answer “no”, but the polygraph identifies some of those answers as lies, making the person ineligible for a job?
A. What is the probability that a job applicant rejected under suspicion of dishonesty was actually trustworthy?
B. Construct a probability tree to find the total probability that were cleared by the polygraph test.
Explanation / Answer
a)
assume there 1000 employees
employees incorrectly identified as not trustworthy
= 950 * 0.15
= 142.5
employees correctly identified as not trustworthy
= 50 * 0.65%
= 32.5
total not trustworthy employees = 142.5 + 32.5 = 175
probability = 142.5/175
= 0.814 or 81.4%
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