trailA flawed safety argument provides little evidence about the risk it assesses
The probability of error in a safety argument bounds the confidence it can provide about low-probability risks
Unknown flaw undermines the chain· for
Complex risk analyses historically exhibit error rates exceeding their claimed risk bounds
Pre-Challenger official estimates of Space Shuttle failure risk were far below the realized failure rate
Nuclear probabilistic risk assessments predicted core-damage frequencies well below the observed historical accident rate
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Bank value-at-risk models understated the frequency of extreme losses before the 2008 financial crisis
Regulatory risk assessments commonly use conservative assumptions that overstate risk
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Graceful degradation of arguments· against
Safety arguments with minor flaws often remain approximately correct
Residual assurance deficits in a safety case can be acceptable when compensated by other arguments and evidence
In adversarial settings, small flaws in a safety argument can be exploited into complete failure
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Evidence assembled in a safety argument retains value even if the argument's reasoning is flawed
Operational and test data provide evidence about system risk independently of the arguments that cite them
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Safety cases are prone to confirmation bias toward a predetermined conclusion of safety
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Incomplete hazard identification is a principal cause of safety assurance failures
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Statistical testing alone cannot demonstrate the ultra-low failure rates required of safety-critical systems
claim · empirical · derivedA factual claim that rests on inference from other evidence rather than direct observation.constitution →claim page ↗︎
A flawed safety argument provides little evidence about the risk it assesses
↓DoubtfulThe evidence weighs against the claim, but the examination is incomplete or the evidence is indirect.constitution →credence 0.30Credence, from 0 to 1: the Steward's probability that the claim, as stated, is true. Stated only where a single number is an honest summary; normative and evaluative claims usually carry none.constitution →
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this rests on ↓
claimA box is a claim: a single proposition the graph assesses, with its own page and map. Click any claim to centre the map on it.constitution →quantityA box with a rule beneath its text is a quantity: a value the graph estimates rather than a proposition it affirms or denies. Its estimate stands where a claim's status would.constitution →questionA rounded box is a question: answered rather than affirmed or denied, with its candidate answers, subquestions and presuppositions beneath it. Its mark says how well answered it is.constitution →argumentA pill is an argument: one line of reasoning stating how the claims beneath it combine to bear on the claim above it, for or against. Click one to see its reasoning and open its page.constitution →✓verifiedThe evidence, examined directly, establishes the claim.constitution →↑supportedThe evidence favors the claim, but the examination is incomplete or the evidence is indirect.constitution →⇄inconclusiveThe evidence and argument have been examined and do not come down on either side.constitution →↓doubtfulThe evidence weighs against the claim, but the examination is incomplete or the evidence is indirect.constitution →✕contradictedThe evidence, examined directly, weighs against the claim.constitution →?unknownInsufficient information to assess.constitution →◌unassessedNo current assessment. Attention goes where its expected value is highest and someone funds it; nothing has funded an assessment of this claim yet, and anyone can.constitution →verified factunsettledvalue premisetheoremprizeA double ring marks a claim with a live prize: an amount in owls offered for a machine-checked proof or disproof of its published formal statement. The amount is in the preview and on the claim page; a prize changes nothing about how the claim is assessed or how important it is judged to be.prize rules →⊢machine-checked⊢ marks a claim whose published formal statement has a machine-checked proof or disproof. The checker confirms the proof; the verdict beside it is still the steward's judgment of the claim as worded.prize rules →supportsthis provides evidence for the parentsteward instructions →contradictsthis argues against the parentsteward instructions →assumesbackground the parent's framing takes as givensteward instructions →requiresa load-bearing premise: the parent is false without itsteward instructions →answersa candidate answer to the questionconstitution →Fig. Detail falls off with distance; every claim is an address.