An evidential reasoning approach for assessing confidence in safety evidence

Safety cases present the arguments and evidence that can be used to justify the acceptable safety of a system. Many secondary factors such as the tools used, the techniques applied, and the experience of the people who created the evidence, can affect an assessor's confidence in the evidence cited by a safety case. One means of reasoning about this confidence and its inherent uncertainties is to present a `confidence argument' that explicitly justifies the provenance of the evidence used. In this paper, we propose a novel approach to automatically construct these confidence arguments by enabling assessors to provide individual judgements concerning the trustworthiness and the appropriateness of the evidence. The approach is based on Evidential Reasoning and enables the derivation of a quantified aggregate of the overall confidence. The proposed approach is supported by a prototype tool (EviCA) and has been evaluated using the Technology Acceptance Model.