Structuring Assurance Cases to Facilitate Effective Certification of Medical Devices

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Software is an enabling technology so good that there is now almost no new device/technology on the market that does not depend on software in some way. As software and devices become increasingly complex and safety features, relying more and more on software, get further intertwined with functional features, the chance of creating serious disasters also dramatically increases. This is especially true in the medical domain where there is tremendous pressure to get new devices onto the market in the hope of saving lives and/or improving quality of life, but where those same devices can cause immense harm if they are not safe for use. Regulatory regimes for software usually rely on checking that an approved development process was used, and then infer from that the software will not contribute to a device failure. Predictably this has not worked well. Safety Cases have been mandatory in several regulatory domains in the UK for many years. Safety cases force manufacturers to provide evidence related to the manufactured product. We are starting to see assurance/safety cases assuming a more prominent role in regulatory regimes in North America. This is especially true in the approach taken by the US FDA in the way they regulate medical devices. Assurance cases are predicated on assumptions that promote satisfactory confidence in the efficacy and safety of the device. These assumptions relate to fundamental issues that have not yet been addressed. I intend to reverse engineer standards to discover the implicit assurance cases embodied therein. I also plan to compare approaches to argumentation from philosophy and formal methods to help create a means by which supporting arguments can be evaluated. My research focuses on determining: i) how to construct and evaluate claims and sub-claims which contribute to the overall dependability and safety of the system; ii) how to evaluate the soundness of arguments in the context of satisfying claims; iii) how to combine evidence of different types to contribute to the confidence that a claim is satisfied; and iv) how to organize the assurance case using a prescribed structure, which will facilitate certifiers being able to build experience in evaluating assurance cases.