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On Signals, Response, and Risk Mitigation: A Probabilistic Approach to the Detection and Analysis of Precursors
Pages 45-60

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From page 45...
... I then briefly discuss the application of this reasonmg to the modeling of terrorist threats md the characteristics of effective organizational warning systems. THE SPACE SHUTTLE In 1988, in the wake of the Challenger disaster, the National Aeronautics and Space Ad ninisrrauon (NASA)
From page 46...
... . As it turns out, a fuel line runs along the external tank on the right side, md because of the way the foam insulation on the external tank is applied, little pieces of insulation had debonded where the fuel line was attached to the tank.
From page 47...
... Even though poorly bonded tiles could withstand the 10-poundsper-square-mch pull test, they could be dislodged either by a large debris hit or, perhaps, even by normal loads, such as high levels of vibration. At JSC, I also asked for the potential trajectories of debris that could debond from the msulation of the external tank, both from the top and the center of the tank (PateCornell and Fischbeck, 1990, 1993b)
From page 48...
... Therefore, the tile maintenance crews sometimes lost some experienced workers. I also learned that tile techmiciams at the time were under considerable pressure to finish work on the spacecraft quickly for the next flight.
From page 49...
... For instance, the wages of tile technicians had been raised, eliminating some of the turnover among those workers, and the nsk-criticality map had been used at KSC to prioritize tile inspections But it appears that at JSC, where maintenance procedures are set, management had concluded that the study did not justify modifying current procedures. As a result, unfortunately, several things that should have been done were not.
From page 50...
... The TREAD Act mandates the creation of an early warning system; the law requires that even minor problems be reported to the National Highway Safety Transportation Administration (DOT-NHTSA, 2001)
From page 51...
... The AIMS reporting system enables the hospital to identify the frequency rod probability of various factors that initiate accident sequences that might hill healthy patients under anesthesia (e.g., people undergoing knee surgery)
From page 52...
... One aspect of the overall failure was the lack of communication among mteltigence agencies. This was pardy the result of laws passed at the end of the Vietnam War that mandated separate databases for separate entities, which deliberately kept agencies from cormnuntcattng with each other.
From page 53...
... Bayesian reasoning involving base rates, as well as the likelihood of the sigmals given the event, can be extremely helpful in addressing this challenge. Bayesian reasoning allows the computing of probabilities in the absence of a large statistical database; it uses logical reasomng based on the prior probability of an event and on the probabilities of errors (both false positives and false negatives)
From page 54...
... Those models are thus unlikely to match actual measurements, which may undermine confidence in the malytical results. In my case, modeling attack scenarios has to be a dynamic exercise.
From page 55...
... First, we must analyze, m parallel, the dynamics of the physical system md of the organization. As Figure 5 shows, a good place to sta t is by identifying the physical weaknesses of a critical system, Using a probabilistic risk analysis, for example, as a basis for setting priorities (look at the engmes before you look at the coffee pot)
From page 56...
... An appropriate alarm level is likely to lead to some false alerts, which have costs. For tnst~mce, a false positive mdicatmg a major terrorist attack could lead to costly hmnan risks for instance, the risks mcurred m a mass evacuation.
From page 57...
... provide a global assessment of a warnung system, the results thus have to be exammed case by case, but the base rates and the rates of errors must be taken Into account. Given the trade-offs between false positives and false negatives, there is no way to resolve the problem of filtering out undesirable signals without making a value judgment.
From page 58...
... Second, managulg the trade-off between false positives and false negatives in warning systems is difficult because it involves the quality of the information, as well as costs and values. Third, to design m effective org~mizational waming system, one has to know where to look The way people m m organization react depends m part on management.
From page 59...
... 1997. Patient risk in mesthesia: probabi i gic risk malysis, m magement effects md improvements.


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