In an article that appears on the website of the American Statistical Asso- ciation (www.amstat.org/meetings/jsm/2000 /usei/gunn.pdf, retrieved April 25, 2017), Carlton Gunn, a public defender in Seattle, Washington, wrote about how he uses statis- tics in his work as an attorney. He states: I personally have used statistics in trying to challenge the reliability of drug testing results. Suppose the chance of a mistake in the taking and processing of a urine sample for a drug test is just 1 in 100. And your client has a "dirty" (i.e., positive) test result. Only a 1 in 100 chance that it could be wrong? Not necessarily. If the vast majority of all tests given- say 99 in 100-are truly clean, then you get one false dirty and one true dirty in every 100 tests, so that half of the dirty tests are false. TD = event that the test result is dirty TC = event that the test result is clean D = event that the person tested is actually dirty C = event that the person tested is actually clean P(TD|D) = 0.99 P(C) = 0.99 P(TD|C) = 0.01 P(D)=0.01 What is the probability of a random test resulting in dirty? (b) 4 What is the probability of person being clean given that their test re- sult is dirty? Is this consistent with the quote given?

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In an article that appears on the website of the American Statistical Asso-
ciation (www.amstat.org/meetings/jsm/2000 /usei/gunn.pdf, retrieved April 25, 2017),
Carlton Gunn, a public defender in Seattle, Washington, wrote about how he uses statis-
tics in his work as an attorney. He states:
I personally have used statistics in trying to challenge the reliability of drug
testing results. Suppose the chance of a mistake in the taking and processing
of a urine sample for a drug test is just 1 in 100. And your client has a "dirty"
(i.e., positive) test result. Only a 1 in 100 chance that it could be wrong? Not
necessarily. If the vast majority of all tests given- say 99 in 100-are truly
clean, then you get one false dirty and one true dirty in every 100 tests, so
that half of the dirty tests are false.
TD = event that the test result is dirty
TC
= event that the test result is clean
D = event that the person tested is actually dirty
C = event that the person tested is actually clean
P(TD|D) = 0.99 P(C) = 0.99
P(TD|C) = 0.01 P(D)=0.01
What is the probability of a random test resulting in dirty?
(b) 4 What is the probability of person being clean given that their test re-
sult is dirty? Is this consistent with the quote given?
Transcribed Image Text:In an article that appears on the website of the American Statistical Asso- ciation (www.amstat.org/meetings/jsm/2000 /usei/gunn.pdf, retrieved April 25, 2017), Carlton Gunn, a public defender in Seattle, Washington, wrote about how he uses statis- tics in his work as an attorney. He states: I personally have used statistics in trying to challenge the reliability of drug testing results. Suppose the chance of a mistake in the taking and processing of a urine sample for a drug test is just 1 in 100. And your client has a "dirty" (i.e., positive) test result. Only a 1 in 100 chance that it could be wrong? Not necessarily. If the vast majority of all tests given- say 99 in 100-are truly clean, then you get one false dirty and one true dirty in every 100 tests, so that half of the dirty tests are false. TD = event that the test result is dirty TC = event that the test result is clean D = event that the person tested is actually dirty C = event that the person tested is actually clean P(TD|D) = 0.99 P(C) = 0.99 P(TD|C) = 0.01 P(D)=0.01 What is the probability of a random test resulting in dirty? (b) 4 What is the probability of person being clean given that their test re- sult is dirty? Is this consistent with the quote given?
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