trailEvidence assembled in a safety argument retains value even if the argument's reasoning is flawed
A flawed safety argument provides little evidence about the risk it assesses
Evidential independence of the data· for
Operational and test data provide evidence about system risk independently of the arguments that cite them
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Selection and scope effects· against
Safety cases are prone to confirmation bias toward a predetermined conclusion of safety
Safety cases are typically produced by the developer or operator of the system being assessed
People seeking evidence for a fixed conclusion tend to select confirming and overlook disconfirming evidence
The Nimrod Review found the Nimrod safety case was a paperwork exercise that missed key dangers
Defeater analysis and independent adversarial review can substantially mitigate confirmation bias in safety cases
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Incomplete hazard identification is a principal cause of safety assurance failures
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Limits of evidence without argument· against
Statistical testing alone cannot demonstrate the ultra-low failure rates required of safety-critical systems
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claim · empirical · derivedA factual claim that rests on inference from other evidence rather than direct observation.constitution →claim page ↗︎
Evidence assembled in a safety argument retains value even if the argument's reasoning is flawed
↑SupportedEvidence favors the claim, but the chain is incomplete or the sources are secondary.constitution →credence 0.85Credence, 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 →
1depended on by
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 →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. Arguments are not destinations; click their claims to explore.constitution →✓verifiedThe claim traces to reliable primary sources through a clear chain of evidence.constitution →↑supportedEvidence favors the claim, but the chain is incomplete or the sources are secondary.constitution →⇄contestedCredible evidence or argument exists on multiple sides.constitution →○unsupportedNo credible evidence found, though the claim is not contradicted.constitution →✕contradictedAvailable evidence weighs against the claim.constitution →?unknownInsufficient information to assess.constitution →◌unassessedNo current assessment — the Steward prioritises higher-importance claims, so this one is likely still queued.constitution →verified factopen questionvalue premisesupportsthis 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 →Fig. — detail falls off with distance; every claim is an address.