Toward a Theory of Assurance Case Confidence

Assurance cases provide an argument and evidence explaining why a claim about some system property holds. This report outlines a framework for justifying confidence in the truth of such an assurance case claim. The framework is based on the notion of eliminative induction-the principle first put forward by Francis Bacon that confidence in the truth of a hypothesis or claim increases as reasons for doubting its truth are identified and eliminated. Possible reasons for doubting the truth of a claim arise from analyzing an assurance case using defeasible reasoning concepts. Finally, the notion of Baconian probability provides a measure of confidence based on how many defeaters have been identified and eliminated.