Understanding What It Means for Assurance Cases to "Work"

This report is the result of our year-long investigation into assurance case practices and effectiveness. Assurance cases are a method for working toward acceptable critical system performance. They represent a significant thread of applied assurance methods extending back many decades and being employed in a range of industries and applications. Our research presented in this report includes a literature survey of over 50 sources and interviews with nearly a dozen practitioners in the field. We have organized our results into seven major claimed assurance case benefits and their supporting mechanisms, evidence, counter-evidence, and caveats.