Health Impact Assessment

Core Idea

Health impact assessment systematically evaluates how proposed policies, projects, or programs affect population health. HIA identifies intended and unintended health consequences before implementation, supporting evidence-based decision-making in non-health sectors like transportation, housing, urban planning, and economic development. HIA is an upstream intervention that shapes the conditions promoting health.

Explainer

From your study of environmental epidemiology, you know how to investigate associations between exposures and health outcomes — measuring how air pollution affects respiratory disease rates, or how contaminated water sources drive infectious disease clusters. Environmental epidemiology is primarily retrospective: it characterizes harms that have already occurred. Health Impact Assessment (HIA) takes the same epidemiological evidence base and deploys it prospectively: before a policy or project is implemented, rather than after. The goal is to predict health effects while there is still time to change course.

HIA follows a structured five-step process. Screening asks whether an HIA is warranted — is the proposal likely to have significant health effects, and will an HIA actually influence the decision? Scoping defines what health outcomes to examine and which populations to focus on. Assessment reviews available epidemiological evidence to estimate likely health impacts, positive and negative. Recommendations translate those findings into specific design changes or mitigation measures. Monitoring and evaluation tracks whether predictions were accurate once implementation occurs. Each step requires combining epidemiological evidence with value judgments about which populations and outcomes matter most — HIA is both a technical and a political process.

The insight that makes HIA valuable is that most determinants of population health lie *outside* the health sector. Your study of health policy revealed how housing quality, transportation infrastructure, employment, education, and food access shape health far more powerfully than medical care. A new highway may reduce commute time, but it also increases air pollution in adjacent neighborhoods, fragments walking infrastructure, and may displace low-income residents — all of which have quantifiable health consequences that a purely transportation-focused analysis would miss. HIA is the mechanism for surfacing those consequences before contracts are signed and concrete is poured.

Classic HIA examples illustrate the upstream logic. A proposed housing development might generate an HIA examining noise exposure from adjacent transit, pedestrian safety, access to green space, and whether unit affordability affects stress-related health outcomes in displaced residents. A proposed minimum wage increase might generate an HIA estimating reductions in food insecurity and mental health burden versus potential employment effects. In each case, the HIA doesn't make the decision — it informs it, ensuring that health costs and benefits are visible to decision-makers and communities alongside economic and logistical considerations. Where environmental impact assessments (EIAs) focus on ecological and physical consequences, HIA explicitly centers human health, including the social and behavioral pathways through which policy shapes population outcomes.