It depends which if the decision involves diagnosing

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Unformatted text preview: ach Decision “Healthy” “Sick” State of the World Healthy Sick P(Correct P(False Rejection) Alarm) P(Miss) P(Hit) Which error is worse? It depends. Which If the decision involves diagnosing breast If cancer, a miss is extremely bad. cancer, If the decision is whether to attack another If country with a nuclear missile, a false alarm is extremely bad. is Suppose the Dr. gets the number of goodies back from the lab and sets his own Response Threshold and β β “Healthy” “Healthy” “Sick” 0.45 0.4 0.4 0.35 0.35 Healthy Sick Probabi l i ty of Di sease 0.3 0.25 0.2 0.15 0.1 0.3 Healthy Sick 0.25 0.2 0.15 0.1 # Goodies in the Blood # Goodies in the Blood As we go from the left to the right panel, we decrease the number of false alarms (“S”|H), but we increase the number of misses (“H”|S) 14 5 13 0 12 5 12 0 11 5 10 0 85 70 55 14 5 13 0 12 5 12 0 11 5 0 10 0 0 85 0.05 70 0.05 55 Probabi l i ty of Di sease 0.45 “Sick” β = 90 goodies “Healthy” “Sick” β = 110 goodies “Healthy” “Sick” Healthy .16 .84 Healthy .84 .16 Sick .02 .98 Sick .50 .50 ROC Curve P(Hit) 1 0.5 0 0 0.2 0.4 0.6 P(False Alarm) 0.8 1 Every point on the ROC curve represents a different response threshold holding accuracy (d’) constant. Moving UP the ROC curve is equivalent to moving the response threshold to the left. Where is the o...
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This document was uploaded on 02/15/2014 for the course PSYCH 002 at Community College of Philadelphia.

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