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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 1 of 18 Value of Information

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 2 of 18 Information Collection - Key Strategy l Motivation – To reduce uncertainty which makes us choose “second best” solutions as insurance l Concept – Insert an information-gathering stage (e.g., a test) before decision problems, as an option D Decision Problem Test Decision Problem

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 3 of 18 Operation of Test EV (after test) > EV (without test) l Why? – Because we can avoid bad choices and take advantage of good ones, in light of test results l Question: – Since test generally has a cost, is the test worthwhile? What is the value of information? Does it exceed the cost of the test? New Information Revision of Prior Probabilities in Decision Problem New Expected Values in Decision Problem

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 4 of 18 Value of Information - Essential Concept l Value of information is an expected value l Expected value after test “k” = p k (D k *) Pk = probablility, after test k, of an observation which will lead to an optimal decision (incorporating revised probabilities due to observation) D k * Expected Value of information = EV (after test) - EV (without test) = p k (D k *) - p k (E j )O ij k k k Test Good - Revise probability Medium Poor

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 5 of 18 Expected Value of Perfect Information - EVPI l Perfect information is a hypothetical concept l Use: Establishes an upper bound on value of any test l Concept: Imagine a “perfect” test which indicated exactly which Event, E j, will occur – By definition, this is the “best” possible information – Therefore, the “best” possible decisions can be made – Therefore, the EV gain over the “no test” EV must be the maximum possible - an upper limit on the value of any test!

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 6 of 18

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 7 of 18 EVPI Example l Question: Should I wear a raincoat? RC - Raincoat; RC - No Raincoat l Two possible Uncertain Outcomes (p = 0.4) or No Rain (p = 0.6) D C C 0.4 0.6 R R NR 5 -10 4 -2 RC R l Remember that better choice is to take raincoat, EV = 0.8

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 8 of 18 EVPI Example (continued) l Perfect test l EVPI Says Rain p = 0.4Take R/C 5 Says No Rainp = 0.6No R/C4 C EV (after test) = 0.4(5) + 0.6(4) = 4.4 EVPI = 4.4 - 0.8 = 3.6

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 9 of 18 Application of EVPI l A major advantage: EVPI is simple to calculate l Notice: – Prior probability of the occurrence of the uncertain event must be equal to the probability of observing the associated perfect test result – As a “perfect test”, the posterior probabilities of the uncertain events are either 1 ot 0 – Optimal choice generally obvious, once we “know” what will happen l Therefore, EVPI can generally be written directly l No need to use Bayes’ Theorem

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 10 of 18 Expected Value of Sample Information - EVSI l Sample information are results taken from an actual test 0 < EVSI < EVPI l Calculations required – Obtain probabilities of test results, p k – Revise prior probabilities p j for each test result TR k => p jk – Calculate best decision D k * for each test result TRk (a k-fold repetition of the original decsion problem) – Calculate EV (after test) = p k (D k *) – Calculate EVSI as the difference between EV (after test) - EV (without test) l A BIG JOB k

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 11 of 18

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 12 of 18 EVSI Example l Test consists of listening to forecasts l Two possible test results – Rain predicted = RP – Rain not predicted = NRP l Assume the probability of a correct forecast = 0.7 p(RP/R) = P(NRP/NR) = 0.7 P(NRP/R) = P(RP/NR) = 0.3 l First calculation: probabilities of test results P(RP)= p(RP/R) p(R) + P(RP/NR) p(NR) = (0.7) (0.4) + (0.3) (0.6) = 0.46 P(NRP)= 1.00 - 0.46 = 0.54

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 13 of 18 EVSI Example (continued 2 of 5) l Next: Posterior Probabilities P(R/RP) = p(R) (p(RP/R)/p(RP)) = 0.4(0.7/0.46) = 0.61 P(NR/NRP) = 0.6(0.7/0.54) = 0.78 Therefore, p(NR/RP) = 0.39 & p(R/RNP) = 0.22

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 14 of 18 EVSI Example (continued 3 of 5) l Best decisions conditional upon test results D C C 0.61 0.39 R R NR 5 -10 4 -2 RC EV = 2.27 EV = -4.54 RP EV (RC) = (0.61) (5) + (0.39) (-2) = 2.27 EV (RC) = (0.61) (-10) + (0.39) (4) = -4.54

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 15 of 18 EVSI Example (continued 4 of 5) D C C 0.22 0.78 R R NR 5 -10 4 -2 RC EV = -0.48 EV = 0.92 NRP EV (RC) = (0.22) (5) + (0.78) (-2) = -0.48 EV (RC) = (0.22) (-10) + (0.78) (4) = 0.92 l Best decisions conditional upon test results

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 16 of 18 EVSI Example (continued 5 of 5) l EV (after test) = p(rain pred) (EV(strategy/RP)) + P(no rain pred) (EV(strategy/NRP)) = 0.46 (2.27) + 0.54 (0.92) = 1.54 l EVSI = 1.54 - 0.8 = 0.74 < EVPI

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 17 of 18 Practical Example - Is a Test Worthwhile? l If value is Linear (i.e., probabilistic expectations correctly represent valuation of outcomes under uncertainty) – Calculate EVPI – If EVPI < cost of testReject test – Pragmatic rule of thumb If cost > 50% EVPIReject test (Real test are not close to perfect) – Calculate EVSI – EVSI < cost of testReject test – Otherwise, accept test

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Dynamic Strategic Planning Massachusetts Institute of Technology Richard Roth Information CollectionSlide 18 of 18 Is Test Worthwhile? (continued) l If Value Non-Linear (i.e., probabilistic expectation of value of outcomes does NOT reflect attitudes about uncertainty) l Theoretically, cost of test should be deducted from EACH outcome that follows a test – If cost of test is known A) Deduct costs B) Calculate EVPI and EVSI (cost deducted) C) Proceed as for linear EXCEPT Question is if EVPI(cd) or EVSI(cd) > 0? – If cost of test is not known A) Iterative, approximate pragmatic approach must be used B) Focus first on EVPI C) Use this to estimate maximum cost of a test

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