Health Impact Assessment (HIA)

The determinants of health

Evidence base of health determinants

An evidence base about the impact that projects, programmes and policies have had on health is required to carry out HIA. The best available evidence is used within the appraisal stage of HIA to determine what impacts may occur (both positive and negative), the size of the impact (if possible) and the distribution of that impact in different population groups. It is generally assumed that the evidence for health impacts exists, and that searching and collating will provide the necessary evidence. Unfortunately this is not often the case, and the evidence of health impacts is often not available. This is because of the long causal pathway between the implementation of a project/programme/policy and any potential impact on population health, and the many confounding factors that make the determination of a link difficult. Within the HIA it is important therefore to be explicit about sources of evidence and to identify missing or incomplete information.

Providing a comprehensive review of the evidence base is not simple. It needs to draw on the best available evidence – that from reviews and research papers, and including qualitative and quantitative evidence. This information must be supplemented with local and expert knowledge, policy information, and proposal specific information.

However, there are examples where the best available evidence has been documented, and in some cases summarised. These are presented below:

  • Transport
  • Food and Agriculture
  • Housing
  • Waste
  • Energy
  • Industry
  • Urbanization
  • Water
  • Radiation
  • Nutrition and health