National and international pressure is growing for public policies and programmes to be prospectively evaluated to determine what their impacts will be on public health. This is evident from statements from bodies including the WHO,1 the European Union,2 and the British Medical Association3and may be seen as a natural development of evidence-based principles that are currently being applied in other health and non health-related fields. But where can policymakers find evidence of health impacts, and how can it be integrated with other influences on decision making? One proposed solution, which is attracting increasing interest, is Health Impact Assessment (HIA).4 However, we suggest that the current formulations of HIA, which combine both health assessment and option-appraisal, may have difficulty fulfilling both roles.

To understand why this might be true, it is worth considering the history and typical methods of HIA. HIA is the offspring of Environmental Impact Assessment and has inherited its major features. It usually begins with a screening process to exclude interventions with no significant health effects. Where health impacts might occur, the process of scoping identifies the kinds of information that …