Importance of Type-II Error and Falsifiability - PowerPoint PPT Presentation

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  1. Importance of Type-II Error and Falsifiability • Hiroyuki MATSUDA • Univ. of Tokyo, • IWC/SC Japan Delegate • WWF Japan Committee Member This Powerpoint file will be uploaded on 1

  2. Precautionary principleRio Declaration 1992, Principle 15 • “In order to protect the environment, the precautionary approach shall be widely applied by States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation. 2

  3. Convention on Biological Diversity JUNE 1992 • “Noting also that where there is a threat of significant reduction or loss of biological diversity, lack of full scientific certainty should not be used as a reason for postponing measures to avoid or minimize such a threat, 3

  4. UN Framework Convention on Climate Change “Where there are threats of serious or ir-reversible damage, lack of full scientific certainty should not be used as a reason for postponing such measures, taking into account that policies and measures to deal with climate change should be cost-effective so as to ensure global benefits at the lowest possible cost. 4

  5. Galileo’s Inquisition Scientists … After • Before the Earth Summit in 1992, • should give no comments to public without full scientific evidence; • keep their result irrespective of public opinion must give some make their opinion a public consensus or win votes No academic rule for what we should say has been established. 5

  6. IUCN Redlist Criteria (2001) 11

  7. Risk analysis is based on a threshold of type-II error. • Type-II: The probability that a species goes extinct when it is not listed as endangered. • Type-I: The probability that a species persists when it is listed as endangered (very small). • Or, If the extinction risk of a species is >10% within next 100 years, it is listed as endangered. 12

  8. G. Mace et al. 1992: Species19:16. • (The validity of criterion A:) “it can result in the listing of some species with very large, apparently secure populations”. (Type-I error) • “However, linking [the rates of de-cline] to population size would exclude the listing of many populations with limited census data.”(Type-II error) 14

  9. Mrosovsky N (1997) Nature389:436 15

  10. Allow criterion E to over-rule other criteria !? • If we do not evaluate extinction risk, we agree with listing a species by criteria other than Criterion E. • We disagree with listing it by criteria A-D if estimated extinction risk is apparently low. • No consensus was made in IUCN Marine Workshop. • About 2/3 of IUCN Criteria Workshop participants disagreed with this option. 16

  11. Risk is usually evaluated under pessimistic assumptions. • IUCN/SSC (p.25) “Assessors should resist an evidentiary attitude and adopt a precautionary but realistic attitude to uncertainty when applying the criteria, for example, by using plausible lower bounds, rather than best estimates, in determining population size...” Therefore, extinction risk based on pessimistic estimates is biased (-fit to avoid type II errors) • We could take risk based on best estimates, and measure type I errors (the weight of evidence).

  12. Japanese plant Red Data Book • Questionnaires: The number of plants and decline rate in each of 4437 map grids in each of ca.2100 threatened? plant species. • Calculate total population size, rate of population decline, extinction risk of each species. • >1500 species are listed in RDB.

  13. >1000 <0.01 <0.1 <0.5 <1 >1 ? total >1000 2 1 1 4 8 + 1.7 + 3.2 >100 2 2 1 3 2 5 15 +12.8 >10 5 16 19 6 2 12 60 + 2.5 >1 1 3 3 2 1 2 12 ? 1 22 23 total 8 23 24 12 6 45 118 +2.8 Unbiased assumption = proportional divide Pessimistic assumption = ignoring unknown grids 38210 Frequency distribution of gridsThe case of primura sieboldii Decline rate within past 10 years Population size 23 extinction 13 Np=f1N1+ f2N2+ f3N3+ f4N5=31977

  14. We define the weight of evidence in plant RDB • Extinction risk: based on pessimistic assumptions (ignoring unknown grids) • Weight of evidence: based on unbiased assumptions (proportional divide) • For 8 CR taxa, 32 EN taxa and 14 VU taxa among 1325 taxa, the weight of evidence within the years in question did not satisfy the extinction risk criteria.

  15. The weight of evidence decreases with increasing number of size unknown grids EN? VU? VU? NT? NT?

  16. How to handle the weight of evidence… • We do not need down-listing even in case of disagreement between scenarios with pessimistic and unbiased estimates (PP) • We should show the weight of evidence for future review process (accountability) • Like weather focast (risk of shower)

  17. Fallacy of applying PP to Maximum Sustainable Yield 6

  18. Threat of biodiversity is serious if the population is below MVP • Minimum viable population (MVP) is defined as threat of demographic stochasticity (e.g., all mothers make sons = 50) and genetic degradation (=500). • The “50/500” law does not guarantee a zero-risk. • If population size > 10,000, the mean time to extinction is usually far too long (I ignore > 1 million yrs). 8

  19. Should any few risk be avoided? (IWC 2001 report, p.93) • Exploitation of whales with environmental variability was still “equivalent to an unsustainable ‘mining’” (still positive risk) • Under the RMP, “the time scales were far too long (1045 years)” (>>the age of cosmos) • “the long time-scale was necessary to examinethe mechanisms of the interaction between environmental variability and exploitation.”???? 9

  20. MSY limit stock level RMP cares just 10% errors Production Catch quota Fishing rate MSY at 60%, 0 catch at 54%

  21. No lower stock limit Fishing is possible until stock collapse Fisheries Management Rule I US and Japan Uncertainty exists not only in whaling, but all fisheries.

  22. Fallacy of applying PP to MSY • If we adopt biased (precautionary) estimates, expected yield is again negatively biased. • MSY should be based on unbiased, most likely estimates (Error in quota is reversible = adaptive management) • MVP should be based on biased estimates, or PP. (Lost of biodiversity is irreversible) • MSY is usually >>MVP, but is <MVP in some local population. 10

  23. Precautionary Approach? • dN / dt = r [1 – (N / K)q] N – fN, • Maximize yield at fMSY = rq / (1 + q). • If estimates of r, K, q and f includes uncertainty, MSY is not achieved, nor extinction risk is not eliminated. • f < fMSY (Precautionary approach) is risk factor not to achieve MSY.

  24. fMSY is neither sufficient nor necessary to stock conservation Low uncertainty in r High uncertainty in r

  25. Conclusion:What is needed for PP • Usually avoid Type II errors (risk-averse) • Say a falsifiable prediction (responsibility of present assessment to the future) • Show the weight of Evidence from unbiased estimates • Non-regret policy (Acceptance of high risk from “good” manners) 17

  26. Anchovy Horse mackerels Pacific saury Chub mackerel Sardine Catch in Japan (1000 mt) Species Replacement of Pelagic Fishes

  27. Cyclic Advantage Hypothesis The next dominant to sardine is anchovy – Yes! As I predicted The second next is chub mackerel Many people agree now Matsuda et al. (1992) Res. Pop. Ecol. 34:309-319

  28. Future of Pelagic Fish Populations in the north-western Pacific: • If overfishing of chub mackerel continues, • Chub mackerel will not recover forever; • If cyclic replacement hypothesis is true, • Sardine will not recover forever; • Do not catch immature mackerel too much • The overfishing is an experiment for my hypothesis. (Adaptive mismanagement)