If a part on a production line is present in an inspection area, a sensor detects it with probability 0.99. If a part is not present, the sensor generates a false alarm with probability 0.02. Assume that the probability of a part being present is 0.1.
a) What is the probability of seeing a false alarm?
b) What is the probability of having a missed detection?
Contingency table for the data given :
True Part on production | |||
No part present | Part present | ||
P(D)=0.9 | P(D)=0.1 | ||
0.9 | 0.1 | ||
Test positive | Test negative | Test positive | Test negative |
2.00% | 98.00% | 99.00% | 1.00% |
False Positive | True Negative | True positive | False negative |
0.018 | 0.882 | 0.099 | 0.001 |
Sensitivty = 0.99 = 99%
Specificity = 0.98 = 98%
(a) P(false alarm) = 0.018 (i.e. sensor generates a false alarm)
(b) P(missed detection) = 0.001 (i.e. false negative- part present but not detected)
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