In 1895 an Italian criminologist, Cesare Lombroso, proposed that blood pressure be used to test
for truthfulness. In the 1930s, William Marston added the measurements of respiration and
perspiration to the process, built a machine to do the measuring, and called his invention the
polygraph or lie detector. Today, the federal courts will not consider polygraph results as
evidence, but nearly half the state courts do permit polygraph tests under certain circumstances.
In addition, its use in screening job applicants is on the rise. Physicians Michael Phillips, Allan
Brett, and John Beary subjected the polygraph to the same careful testing given to medical
diagnostic tests. They found that if 1,000 people were subjected to the polygraph and 500 told
the truth and 500 lied, the polygraph would indicate that approximately 185 of the truth-tellers
were liars and that approximately 120 of the liars were truth-tellers (%u201CLie Detectors Can
Make a Liar out of You,%u201D Discover, June 1986).
1. In the application of a polygraph test, an individual is presumed to be a truth-teller (H0) until
%u201Cproven%u201D a liar (H1). In this context, what is a Type I error? A Type II error?
2. According to Phillips, Brett, and Beary, what is the probability (approximately) that a
polygraph test will result in a Type I error? A Type II error?
PLEASE ANSWER BOTH QUESTIONS.
Solution
Type I Error=\"claiming that the person is liar when in fact s/he is a truth-teller\"
Type II Error=\"claiming that the person is a truth-teller when in fact s/he is a liar\".
In 1895 an Italian criminologist, Cesare Lombroso, proposed that blo.pdf
1. In 1895 an Italian criminologist, Cesare Lombroso, proposed that blood pressure be used to test
for truthfulness. In the 1930s, William Marston added the measurements of respiration and
perspiration to the process, built a machine to do the measuring, and called his invention the
polygraph or lie detector. Today, the federal courts will not consider polygraph results as
evidence, but nearly half the state courts do permit polygraph tests under certain circumstances.
In addition, its use in screening job applicants is on the rise. Physicians Michael Phillips, Allan
Brett, and John Beary subjected the polygraph to the same careful testing given to medical
diagnostic tests. They found that if 1,000 people were subjected to the polygraph and 500 told
the truth and 500 lied, the polygraph would indicate that approximately 185 of the truth-tellers
were liars and that approximately 120 of the liars were truth-tellers (%u201CLie Detectors Can
Make a Liar out of You,%u201D Discover, June 1986).
1. In the application of a polygraph test, an individual is presumed to be a truth-teller (H0) until
%u201Cproven%u201D a liar (H1). In this context, what is a Type I error? A Type II error?
2. According to Phillips, Brett, and Beary, what is the probability (approximately) that a
polygraph test will result in a Type I error? A Type II error?
PLEASE ANSWER BOTH QUESTIONS.
2. Solution
Type I Error="claiming that the person is liar when in fact s/he is a truth-teller"
Type II Error="claiming that the person is a truth-teller when in fact s/he is a liar"
