Health Impact Assessment (HIA) has been defined as ‘a combination of procedures, methods and tools by which a policy, programme or project may be judged as to its potential effects on the health of a population, and the distribution of those effects within the population’ (WHO, 1999d). Policy makers can use this tool to assess which particular policies would offer the best potential for reducing particular health gaps between socio-economic groups and to identify and remove particular aspects from existing policies that appear to be widening the health gap between different socio-economic groups.

The HIA process involves five steps (WHO, 2008a):

1. screening: quickly establishing the health relevance of a policy or project and whether an HIA is needed;
2. scoping: identification of key health issues and public concerns, to establish a terms of reference and to set boundaries;
3. appraisal: a rapid an in-depth assessment of health impacts using available evidence (i.e. who will be affected, baseline, prediction, significance, mitigation);
4. reporting: conclusions and recommendations to remove/mitigate negative impacts on health or to enhance positive impacts;
5. monitoring: action, where appropriate, to monitor actual impacts on health to enhance existing evidence base.

An explanation of the different stages in this process and particular case studies in which the procedure has been implemented can be found on the World Health Organisation website.