Research has shown that specific biochemical markers are found exclusively in th
ID: 60475 • Letter: R
Question
Research has shown that specific biochemical markers are found exclusively in the breath of patients with lung cancer. However, no lab test can currently distinguish the breath of lung cancer patients from that of other subjects. Could dogs be trained to identify these markers in specimens of human breath, as they can be to detect illegal substances or to follow a person’s scent? An experiment trained dogs to distinguish breath specimens of lung cancer patients from breath specimens of control individuals by using a food-reward training method. After the training was complete, the dogs were tested on new breath specimens without any reward or clue using a double-blind, completely randomized design. Here are the results for a random sample of 1286 breath specimens:
Dog test result
Breath specimen from a
Control subject
Cancer subject
a, The sensitivity of a diagnostic test is its ability to correctly give a positive result when a person tested has the disease, or P(positive test|disease). Find the sensitivity of the dog cancer-detection test for lung cancer
b, The specificity of a diagnostic test is the conditional probability that the subject tested doesn’t have the disease, given that the test has come up negative. Find the specificity of the dog cancer-detection test for lung cancer.
c, Draw a tree diagram for this study. And indicting probability for each branch of the tree.
Dog test result
Breath specimen from a
Control subject
Cancer subject
total Negative 708 10 718 Positive 4 564 568 Total 712 574 1286Explanation / Answer
a) Sensitivity:
Sensitivity is the ability of a test to correctly identify the patients carrying the disease. It is the frequency of positive result when disease is present
Sensitivity = True Positives/( True Positives + False Positives)
= 564 /(564 + 10)
=564/574
= 0.98
b) Specificity:
Specificity is the ability of the test to correctly identify patients without the disease. It is the frequency of negative result when disease is absent
Specificity = True Negatives/( True Negatives + False Negatives)
= 708 / (708 + 4)
= 708/712
= 0.99
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