Chapter 5: Q. 4 (page 309)
Liar, liar! Sometimes police use a lie detector test to help determine whether a suspect is
telling the truth. A lie detector test isn鈥檛 foolproof鈥攕ometimes it suggests that a person is
lying when he or she is actually telling the truth (a 鈥渇alse positive鈥). Other times, the test
says that the suspect is being truthful when he or she is actually lying (a 鈥渇alse negative鈥).
For one brand of lie detector, the probability of a false positive is 0.08.
a. Explain what this probability means.
b. Which is a more serious error in this case: a false positive or a false negative? Justify
your answer.
Short Answer
a) The probability of the mammogram's false-negative rate must be interpreted.
b) We predict that around of people who take a polygraph.
