Decisionmakers today largely assess emergency preparedness and homeland security "in the rear view mirror," looking at performance in actual events and responding to perceived failures. While learning from real-world experience is important, better ways to assess preparedness prospectively will lead to better choices as to how and where to strengthen it. This paper frames a broad set of questions about how preparedness can be meaningfully measured and lays out some of the ingredients needed to answer them. To simplify the discussion, it focuses on response activities-the near-term actions taken by responder organizations when a disaster or terrorist incident is occurring or in its immediate aftermath that are intended to limit its consequences. It also provides some background on the national preparedness system and on current approaches for assessing emergency preparedness, and it introduces the concept of response reliability, an alternative way of thinking about measuring preparedness that can answer the public's and policy makers' fundamental question: How certain should we as a nation be that the systems we have put in place to respond to damaging events will be able to deliver when called upon?

Framing the issue / Background. The national preparedness system -- How is preparedness assessed now? / Potential options and solutions. An example reliability assessment -- Thinking through assessing response reliability -- Advantages of using reliability measures for preparedness evaluation / How might the impact of this approach be evaluated?.