An HIA can vary in its level of in-depth assessment and in the resources needed. The most basic form of HIA requiring the least amount of resources is the desktop HIA. This type of HIA is most appropriate for policies or interventions that are expected to have only little impact on health. A desktop HIA usually takes a few hours to a few weeks and in general uses existing knowledge and evidence that is being discussed among a small number of participants. In a desktop HIA there is normally no engagement of the community and only the most relevant external stakeholders are consulted. If the desktop HIA reveals that there are more health impacts than expected, the desktop HIA can be seen as a screening exercise to a more extensive HIA.
A more extensive, and the most common form of HIA is the rapid HIA. This type of HIA is appropriate for most policies and interventions. A rapid HIA usually takes a few days to a few weeks and in general involves a small steering group, a stakeholder workshop and includes community involvement. A rapid HIA is expected to include the analysis of the health impact by reviewing literature and analysing existing data with respect to the expected health effects. Within a rapid HIA there is no large scale primary data collection. It does involve the gathering of some additional knowledge and evidence from a small number of stakeholders.
The most extensive form of HIA is the comprehensive HIA. This type of HIA distinguishes itself from the other two types by the collection of new primary data in the field. This type of HIA requires the largest investment of resources and can take months to complete. It is especially suited for large and complex policies or interventions.
Whether it is appropriate to carry out a desktop HIA, a rapid HIA, a comprehensive HIA or anything in between is determined by the likelihood and magnitude of expected impacts on health and health inequalities and the expected footprint of the project (e.g. resources, area affected, complexity). The social sensitivity of the project should also be considered. Figure 33 provides some guidance how to decide which type of HIA is appropriate.