Abstract
Health impact assessment (HIA) is a systematic and flexible tool, which is advocated by the World Health Organisation as a method through which to consider the impact of policies on the health and well-being of a population, and the inequalities that may arise because of it. In 2018, the HIA support unit in Wales carried out a comprehensive and unique HIA on the impact of Brexit in Wales. The aims were to understand the differential impacts that Brexit would have on the health and well-being of the population and to provide evidence to inform decision makers across a range of public bodies. It followed a five-step process for HIA and utilised a wide range of evidence sources and health intelligence including both quantitative and qualitative evidence. This paper reflects on the process of carrying out the HIA and the methods used. It discusses the stages of the HIA, and shares the findings and reflections of implementation which will be beneficial to other HIA practitioners and policy makers. It does not concentrate on the findings of the HIA in detail, but focusses on what worked and any challenges encountered. It has been used to progress the practice of HIA in Wales and demonstrates the value of HIA as a method to inform and influence complex decisions.