Health impact assessment can be defined as a structured framework of procedures, methods, and tools that uses scientific data, expert judgment, and stakeholder consultation to identify and evaluate the potential (or actual) effects of various proposed actions, plans, and policies on the health of a population group. Based on this assessment, actions can be taken to reduce adverse health effects and optimize the benefits of planned decisions (National Academy of Sciences, 2011, pp. 14-17).

The framework includes several basic steps, depending on the subject of the assessment (National Academy of Sciences, 2011, p. 7):

1. Screening of the proposed action, plan, or policy – description of the timeframe and political and other context; assessment of the expected health impact, the resources needed to conduct a health impact assessment, and the need for such an assessment;

2. Scoping – summarizing the health indicators to be assessed; identifying the affected population groups; description of the research question, data sources, and analytical plan; identification of alternatives to the proposal being assessed; summary of stakeholder engagement and issues of importance to stakeholders;

3. Assessment – description of the existing health status of the population prior to undertaking the action being assessed; analysis of the health effects of the proposed action and its alternatives; description of the limitations of the analysis and the associated uncertainty; description of the assessment methodology; consideration of the opinions of stakeholders;

4. Proposals for alternatives to the proposed actions that would reduce the negative and increase the positive effects on health; identification of stakeholders who could implement the proposals based on the assessment; selection of monitoring indicators and verification system;

5. Reporting – documenting of the entire process and its steps; communication of the assessment results to decision-making institutions, the public, and other stakeholders;

6. Monitoring and evaluation – tracking changes in health indicators and implementing proposals made on the basis of the evaluation.

Quantitative health impact assessment differs from qualitative assessment. It is not enough to conclude that a given level of exposure has a positive or negative effect on health. The availability of calculated changes in quantitative public health indicators provides expanded practical guidance for cost-benefit analyses, detailed resource allocation, or forecasts of the burden on investment, social, and health systems.

These assessments are based on baseline data on the relationship between the level of a given exposure and its impact (also referred to as dose-response, exposure-response, concentration-response, or exposure-effect functions), which is derived from appropriately designed epidemiological studies. It is preferable to use such relationships obtained from large-scale cohort studies that use accurate methods for assessing pollutants, take into account the influence of confounding factors, and are sufficiently representative in terms of variability in sample characteristics (Rigaud et al., 2024). The results of more than one study, when available, are most often combined to ensure greater stability and reliability of such a relationship.

Other input data used for these calculations include the total size of the population at risk and the number of individuals exposed to given levels of the environmental factor. The latter may be grouped into two or more groups, for example, individuals exposed to concentrations above a certain regulatory or health-based threshold or to different categorized levels of pollution. This information can be used to determine the total attributable fraction in the population, i.e. what proportion or percentage of cases of a given disease over a given period of time are attributable to exposure. As a next step, this health loss could be converted into a monetary equivalent, taking into account the direct and indirect costs expected due to temporary or permanent disability, use of medical care, loss of productivity, and premature death.

A commonly used method for quantitative health impact assessment is to compare the impact at the existing level of an environmental factor with that at an alternative higher or lower level, which is defined as a counterfactual health impact assessment (Murray et al., 2004). Other more advanced methods are the Proportional multi-state life table (Mytton et al., 2017; Blakely et al., 2020) using a synthetic population that is tracked for a certain period of time (Woodcock et al., 2018), and agent-based simulation models, which originated in transport planning (Kanj et al., 2025). A comparison of the different methods is provided by Mueller et al. (2023).

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Health impact assessment example

Khomenko S, Burov A, Dzhambov AM, de Hoogh K, Helbich M, Mijling B, Hlebarov I, Popov I, Dimitrova D, Dimitrova R, Markevych I, Germanova N, Brezov D, Iungman T, Montana F, Chen X, Gehring U, Khreis H, Mueller N, Zapata-Diomedi B, Zhang J, Nieuwenhuijsen M. Health burden and inequities of urban environmental stressors in Sofia, Bulgaria. Environ Res. 2025 Aug 15;279(Pt 1):121782. doi: 10.1016/j.envres.2025.121782.

References

Blakely T, Moss R, Collins J, Mizdrak A, Singh A, Carvalho N, Wilson N, Geard N, Flaxman A. Proportional multistate lifetable modelling of preventive interventions: concepts, code and worked examples. Int J Epidemiol. 2020;49(5):1624-1636. doi: 10.1093/ije/dyaa132.

European Commission: Directorate-General for Mobility and Transport, CE Delft, Essen, H. van, Fiorello, D., El Beyrouty, K., Bieler, C., Wijngaarden, L. van, Schroten, A., Parolin, R., Brambilla, M., Sutter, D., Maffii, S., & Fermi, F. (2020). Handbook on the external costs of transport – Version 2019 – 1.1. Publications Office. https://data.europa.eu/doi/10.2832/51388

Mueller N, Anderle R, Brachowicz N, Graziadei H, Lloyd SJ, de Sampaio Morais G, Sironi AP, Gibert K, Tonne C, Nieuwenhuijsen M, Rasella D. Model Choice for Quantitative Health Impact Assessment and Modelling: An Expert Consultation and Narrative Literature Review. Int J Health Policy Manag. 2023;12:7103. doi: 10.34172/ijhpm.2023.7103.

Mytton OT, Tainio M, Ogilvie D, Panter J, Cobiac L, Woodcock J. The modelled impact of increases in physical activity: the effect of both increased survival and reduced incidence of disease. Eur J Epidemiol. 2017;32(3):235-250. doi: 10.1007/s10654-017-0235-1.

National Academy of Sciences. (2011). Improving health in the United States: The role of health impact assessment (pp. 7; 14–17). The National Academies Press. https://doi.org/10.17226/13229

National Academy of Sciences. Improving Health in the United States: The Role of Health Impact Assessment. Washington: The National academy of sciences press; 2011, p. 14-17. ISBN-13: 978-0-309-21883-2

Nieuwenhuijsen MJ, Khreis H, Verlinghieri E, Mueller N, Rojas-Rueda D. Participatory quantitative health impact assessment of urban and transport planning in cities: A review and research needs. Environ Int. 2017;103:61-72. doi: 10.1016/j.envint.2017.03.022.

Rigaud M, Buekers J, Bessems J, Basagaña X, Mathy S, Nieuwenhuijsen M, Slama R. The methodology of quantitative risk assessment studies. Environ Health. 2024;23(1):13. doi: 10.1186/s12940-023-01039-x.

Williams H, Andersen ZJ, Boogaard H, Brage S, Browning MHEM, Cai S, Chen X, deSouza P, Dzhambov AM, Fenech B, Flower G, Forastiere F, Garcia L, Gasparrini A, Gehring U, Gowers AM, Hoek G, Khomenko S, Lim CC, Lu C, Mitsakou C, Pozzer A, Ramani T, Roscoe C, Spadaro JV, Tatah L, Vienneau D, Woodcock J, Yeager R, Zapata-Diomedi B, Nieuwenhuijsen M, Khreis H. Expert perspectives on exposure-response functions for urban health policy: Lessons from a UBDPolicy workshop. Environ Res. 2026;288(Pt 1):123150. doi: 10.1016/j.envres.2025.123150.

Woodcock J, Abbas A, Ullrich A, Tainio M, Lovelace R, Sá TH, Westgate K, Goodman A. Development of the Impacts of Cycling Tool (ICT): A modelling study and web tool for evaluating health and environmental impacts of cycling uptake. PLoS Med. 2018;15(7):e1002622. doi: 10.1371/journal.pmed.1002622.

Woodcock J, Tatah L, Anciaes P, Andersen Z, Bardhan R, Chen X, de Nazelle A, Gehring U, Gössling S, Helbich M, Hoek G, Labib SM, Khomenko S, Khreis H, MacCarthy D, Mindell JS, Saadi I, Schweiggart N, Tonne C, Thondoo M, van den Broek d’Obrenan H, Zapata-Diomedi B, Nieuwenhuijsen M. Quantitative Health Impact Assessment of Environmental Exposures Linked to Urban Transport and Land Use in Europe: State of Research and Research Agenda. Curr Environ Health Rep. 2025;12(1):38. doi: 10.1007/s40572-025-00505-7.