Health system spending, and the consequent impact on health are increasingly a focus of governments around the world. Given the strain on resources and systems, increasingly scarce resources require targeting more effectively. Measuring efficiency and productivity are increasingly the focus of government gepartments, both nationally and locally. Thus, assessing how efficiency is measured and how valid and robust results are is critical to those involved in policy and service delivery. This chapter presents revised guidelines as to how users should set up such studies to be as useful as possible and how end users can assess how useful they actually are to them in their specific setting. Conclusions are drawn as to how these can be used in a fast-changing world, and potential consequences of not following guidance are discussed.