Epidemiology, Population Health, and Health Impact Assessment

The health of populations depends on many different factors. Epidemiology is a discipline that has a crucial role in describing health status, identifying risk factors, and analyzing relationships between health and different hazardous agents. The classical epidemiological triangle of host-agentenvironment describes how individuals become ill. Disease occurs when an outside agent (vector) capable of causing disease or injury meets a host that is vulnerable to the agent. This happens in an environment that allows the agent and host to interact. Epidemiology not only measures the relationships between hosts and agents in certain environments but also analyses the health status of the population living in that environment. As epidemiology is one of the essential disciplines of public health, its major aim is to contribute to fulfilment of the definition of public health as “a science and art to promote health and prevent disease by organized effort of society”.1 However, to improve the health status of the population, the knowledge produced by epidemiology needs to be used and translated into interventions. Epidemiology has a long tradition and has created a wealth of accumulated experience to assess micro-environments and specific agents that may impact health. However, epidemiology has been infrequently applied to assessment of public health issues at the policy or strategic level. In addition, epidemiology itself does not equip to deal with dialogue between stakeholders within its scientific discipline. There are different types of interventions tackling all three elements of the triangle. One can work with hosts and improve their immune system, increase their knowledge, and motivate behavioral change to make the hosts more resistant to agents. Public health can also influence the presence and distribution of agents (vectors); this is often done via traditional hygiene measures, such as provision of safe drinking water, clean air, and good waste management, but also via anti-smoking regulations, diet advice, and physical activity guidelines. However, tackling the environment is a bit more difficult. If we consider the “micro-environment”, we are still on the host level and employ interventions like those mentioned above. If we are considering the “macro-environment”, as described, for example, by Dahlgren & Whitehead’s2 model of health (later modified by Barton and Grant3), different intervention methods need to be applied. This model of health is influenced by general political, social, and environmental conditions, and a set of social determinants of health, including work, education, culture, social cohesion, and individual behavior, as well as biological factors like age, sex, and genetics. Health impact assessment (HIA) aims to influence general social, political, and environmental factors, as well as the social determinants of health. Because the goal of HIA is to assess potential future impacts of projects, plans, strategies, and policies on health,4 HIA projects intervene in the environment. Although there are several definitions of HIA and a confusion remains about what is and what is not HIA, the following three conditions must be met to be considered HIA: 1. A policy, project, programme, or plan is assessed and a decision upon it is expected to be taken; 2. Distribution of effects across the population is described; and 3. Dialogue between relevant stakeholders (stakeholders’ participation) is established. HIA is based on values of democracy, equity, sustainable development, and ethical use of evidence.4 It is a multidisciplinary method that is open to experts of different disciplines (including epidemiologists, who are some of the key experts involved) and the public. All of these stakeholders constitute the steering group, which usually directs an HIA. These key conditions suggest how epidemiology contributes to HIA and why HIA is needed beyond epidemiology. One should understand the environment in its broadest possible sense; the social, economic, cultural, political, and