Decision Analysis
What kinds of problems? Alternatives known States of Nature and their probabilities are known. Payoffs computable under different possible scenarios
Basic Terms Decision Alternatives States of Nature (eg. Condition of economy) Payoffs ($ outcome of a choice assuming a state of nature) Criteria (eg. Expected Value)
Example problem
Expected Values
Decision Tree 300 0.3 340 0.6 350 0.1 400 A1 -100 0.3 A2 0.6 600 A2 400 400 0.1 700 A3 0.3 -1000 0.6 -200 -300 0.1 1200
Sequential Decisions Would you hire a consultant (or a psychic) to get more info about states of nature? How would additional info cause you to revise your probabilities of states of nature occuring? Draw a new tree depicting the complete problem.
Consultant’s Track Record
Probabilities P(F/S1) = 0.2 P(U/S1) = 0.8 P(F/S2) = 0.6 P(U/S2) = 0.4 F= Favorable U=Unfavorable
Joint Probabilities
Posterior Probabilities P(S1/F) = 0.06/0.49 = 0.122 P(S2/F) = 0.36/0.49 = 0.735 P(S3/F) = 0.07/0.49 = 0.143 P(S1/U) = 0.24/0.51 = 0.47 P(S2/U) = 0.24/0.51 = 0.47 P(S3/U) = 0.03/0.51 = 0.06
Solution Solve the decision tree using the posterior probabilities just computed.