1) A public health researcher studying auto accidents questions whether broken b

Question

1) A public health researcher studying auto accidents questions whether broken bones and concussions are independent events in injury accidents. From emergency room records he estimates the following probabilities, where B represents one or more broken bone, and C represents a concussion:

2) A medical device developer tests a new instrument intended to detect skin cancers, comparing instrument results to biopsy results (the "gold standard"). In a test of 1000 subjects, the testers obtain the following results:

What are the sensitivity and specificity of the instrument in detecting skin cancer?

instrument biopsy cancerous biopsy benign total cancerous 320 30 350 benign 80 570 650 total 400 600 1000

Explanation / Answer

P(B and C) = P (B) + P (c) - P (B U C)

= 0.45 + 0.32 - 0.55

= 0.22

2) sensitivity = 320/400 = 0.8

Specificity = 570/600 = 0.95

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