Health impact assessment (HIA) is used as a tool for decision makers to address health inequalities in local populations. The purpose of HIA is to identify the potential health consequences of a proposal on a given population and to maximize the positive health benefits and minimize the potential adverse effects on health and inequalities . Mindell et al. (2004) distinguish it from other tools used to aid decision making as:

• It focuses on complex interventions or policy and their diverse effects on determinants of health.
• It requires evidence on the reversibility of adverse factors damaging to health.
• It involves a diversity of evidence in terms of relevant disciplines, study designs, quality criteria and sources of information.
• It involves a broad range of stakeholders.
• It is often required within short timescales and limited resources.
• It involves a degree of pragmatism to assemble information to inform decision makers regardless of the quality of the evidence.

HIA provides a useful means, therefore, of improving knowledge about the potential impact of a policy or programme, which can inform decision-makers and those who might be affected. It can facilitate adjustment of the proposed policy in order to mitigate the negative and maximize the positive impacts (WHO, 1999).

In this approach, in addition to promoting the maximum health of the population, four values are particularly important for HIA:

• Democracy: emphasizing the right of people to participate in a transparent process for the formulation, implementation and evaluation of policies that affect their life, both directly and through elected political decision makers.
• Equity: emphasizing that HIA is not only interested in the aggregate impact of the assessed policy on the health of a population but also on the distribution of the impact within the population, in terms of gender, age, ethnic background and socioeconomic status.
• Sustainable development: emphasizing that both short-term and long-term, as well as more and less direct, impacts are taken into consideration.
• Ethical use of evidence: emphasizing that the use of quantitative and qualitative evidence has to be rigorous, and based on different scientific disciplines and methodologies to get as comprehensive an assessment as possible.