Develop a matrix for the following situation and calculate accuracy, true negative rate, and true positive rate. The illustrations from this unit’s studies are linked in Resources.
Comment on the utility of the test—does it work well? Do you think police departments would find this test acceptable? What about defense attorneys? Interpret accuracy, true negative rate, and true positive rate for this scenario:
Police departments need to test drivers for blood alcohol levels when they suspect the driver may be under the influence of alcohol. Blood alcohol tests are expensive and are invasive, requiring a blood sample. Breathalyzer tests provide preliminary test results that can establish probable cause for police officers to arrest an individual and take them for a formal blood alcohol test. Bringing a person in for a formal test when they really are not drunk creates ill will for a police department. Not detecting a truly drunk driver could lead to a tragic accident. Your firm has developed a new breathalyzer test and has the following results:
One hundred subjects were tested with your new device. Sixty subjects were truly drunk and 40 were not drunk. Of the 60 drunk subjects, the test correctly identified 58 as being drunk and incorrectly identified two as not drunk when they in fact were drunk. Of the 40 not drunk subjects, 22 were correctly identified as not drunk and 18 were incorrectly identified as drunk.
Second, assume that the test above generates an ROC curve labeled B in Figure 5-10 on page 217. Another test is identified that generates an ROC curve labeled A on Figure 5-10 on page 217. Which test is preferred? Why?