In the pursuit of design excellence, you might want usability test participants to interact with a medical device in every conceivable way. However, design complexities and limited duration test sessions might make this an infeasible goal, requiring you to set priorities. If you have to prioritize, be sure to focus on safety-critical tasks and those that will have a substantial in‘uence on task effectiveness and user satisfaction. When you move from conducting formative usability tests to a summative usability test, focus even more attention the highest-priority, safety-critical tasks and link your selected tasks to risk management and analysis efforts.