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An Investigation of Proposed Techniques for Quantifying Confidence in Assurance ArgumentsThe use of safety cases in certification raises the question of assurance argument sufficiency and the issue of confidence (or uncertainty) in the argument's claims. Some researchers propose to model confidence quantitatively and to calculate confidence in argument conclusions. We know of little evidence to suggest that any proposed technique would deliver trustworthy results when implemented by system safety practitioners. Proponents do not usually assess the efficacy of their techniques through controlled experiment or historical study. Instead, they present an illustrative example where the calculation delivers a plausible result. In this paper, we review current proposals, claims made about them, and evidence advanced in favor of them. We then show that proposed techniques can deliver implausible results in some cases. We conclude that quantitative confidence techniques require further validation before they should be recommended as part of the basis for deciding whether an assurance argument justifies fielding a critical system.
Document ID
20160006526
Acquisition Source
Langley Research Center
Document Type
Technical Memorandum (TM)
Authors
Graydon, Patrick J.
(NASA Langley Research Center Hampton, VA, United States)
Holloway, C. Michael
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
May 24, 2016
Publication Date
May 1, 2016
Subject Category
Quality Assurance And Reliability
Statistics And Probability
Report/Patent Number
NASA/TM-2016-219195
NF1676L-23680
L-20670
Funding Number(s)
WBS: WBS 999182.02.50.07.02
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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