Conducting Health Impact Assessments

Conducting Health Impact Assessments

Why This Skill Exists

Health Impact Assessments (HIAs) evaluate the potential health effects of proposed policies, programs, plans, or projects before they are implemented. Unlike environmental impact assessments (EIAs), HIAs specifically center population health and health equity, examining how decisions in non-health sectors — transportation, housing, land use, energy, agriculture — affect health determinants. The practice draws on the Gothenburg Consensus Paper (WHO 1999), the NRC risk assessment paradigm (hazard identification, dose-response, exposure assessment, risk characterization), and the Health Impact Project (Pew/RWJF) minimum elements. HIAs are required or recommended in several state and local jurisdictions and are a key tool for Health in All Policies (HiAP) initiatives. This skill structures the complete HIA process from screening through monitoring.

The Health in All Policies (HiAP) movement has expanded HIA practice beyond environmental health into housing, transportation, education, economic development, and criminal justice policy. The National Academies' 2011 report "Improving Health in the United States: The Role of Health Impact Assessment" established minimum practice standards. As of 2024, over 500 HIAs have been completed in the U.S., with increasing emphasis on health equity analysis as a core component.

Checkpoint A — Intake and Scoping

Intake Questions

1. What is the proposed decision (policy, project, or plan) being assessed?
2. Who is the decision-maker and what is the decision timeline?
3. What populations will be affected, and which subpopulations are most vulnerable?
4. Has a screening determination already been made that an HIA is warranted?
5. What health determinants are likely to be affected (air quality, housing, food access, physical activity, social cohesion, economic opportunity)?
6. What existing data sources are available for the affected community?
7. Is this a rapid HIA (desk-based, 4-8 weeks), intermediate HIA (some primary data, 3-6 months), or comprehensive HIA (extensive primary data, 6-18 months)?
8. What community engagement resources are available for participatory input?

Required Documents

• Proposal documentation (project plans, policy drafts, zoning applications, environmental review documents)
• Demographic and health profile of the affected community (Census/ACS, vital records, BRFSS, County Health Rankings)
• CDC/ATSDR Social Vulnerability Index (SVI) for the affected geography
• Existing Environmental Impact Statement (EIS) or Environmental Assessment (EA) if applicable
• Prior HIAs conducted in the same jurisdiction or for similar proposals
• Health in All Policies framework adopted by the jurisdiction (if any)
• Stakeholder map identifying community organizations, advocacy groups, and affected residents

Step 1 — Screening

Determine whether an HIA is warranted and feasible:

• Health relevance: Does the proposal have a plausible pathway to affecting health? Assess through a pathway diagram linking the proposal to intermediate determinants to health outcomes.
• Decision relevance: Is the decision still open? Can health information influence the outcome?
• Added value: Is health adequately addressed in existing review processes (EIA, regulatory review)? If not, HIA adds value.
• Feasibility: Are data, expertise, time, and budget sufficient for a credible assessment?

Document the screening decision. If an HIA is not warranted, explain why. If warranted, specify the type (rapid, intermediate, or comprehensive) and proceed.

Step 2 — Scoping

Define the boundaries and methods of the HIA:

• Identify the health determinants and outcomes to be assessed. Use a causal pathway diagram: Proposal → Change in determinant → Change in exposure/behavior → Health outcome.

• Prioritize pathways based on: magnitude of potential impact, severity of health outcome, size of affected population, and vulnerability of subpopulations.

• Select assessment methods for each pathway: literature review, quantitative modeling (exposure modeling, burden-of-disease calculation, health economic analysis), qualitative analysis (community input, expert judgment), or spatial analysis (GIS).

• Define the geographic and temporal scope of the assessment.

• Develop a stakeholder engagement plan: identify who will be consulted, how community input will be collected (focus groups, public comment, participatory mapping), and how input will influence the assessment.

• Establish the assessment team and their roles.

• Health equity scoping --- Explicitly identify vulnerable subpopulations in the scoping phase: low-income communities, communities of color, children, elderly, persons with disabilities, unhoused persons, and recently arrived immigrants. For each subpopulation, assess baseline health status, cumulative environmental burden (using CalEnviroScreen or EPA EJScreen), and differential exposure to the proposed decision's effects.

Step 3 — Assessment

For each prioritized pathway, characterize the baseline and predicted impact:

• Baseline health profile: Current prevalence, incidence, and distribution of relevant health outcomes in the affected population. Use BRFSS, vital records, hospital discharge data, and CDC WONDER.
• Exposure assessment: Quantify the expected change in exposure or health determinant resulting from the proposal. For air quality, use dispersion modeling (AERMOD) or health impact functions from EPA BenMAP-CE. For transportation, use traffic modeling and pedestrian injury data. For housing, use housing quality indices and displacement metrics.
• Dose-response/effect estimation: Apply published exposure-response relationships from peer-reviewed literature or systematic reviews. For PM2.5, use EPA's concentration-response functions for mortality and morbidity. For noise, use WHO Environmental Noise Guidelines.
• Impact characterization: Estimate the number of affected individuals and the magnitude and direction (positive or negative) of expected health changes. Express impacts quantitatively where possible (e.g., estimated additional asthma ED visits per year) and qualitatively where data are insufficient.
• Equity analysis: Assess whether impacts are distributed disproportionately across subpopulations by race/ethnicity, income, age, disability, or geography. Use CDC SVI to identify vulnerable census tracts.
• Uncertainty analysis: Characterize the confidence level for each impact estimate (high, moderate, low) based on evidence quality, model assumptions, and data gaps.

Common HIA Quantitative Methods Reference

Step 4 — Recommendations

Develop evidence-based recommendations to mitigate negative health impacts and enhance positive ones:

• For each identified negative impact, propose specific mitigation measures with expected effectiveness.
• For each identified positive impact, propose enhancement measures to maximize benefit.
• Prioritize recommendations by: health impact magnitude, feasibility, cost, equity benefit, and alignment with community priorities.
• Frame recommendations in actionable terms for the decision-maker (e.g., "Require MERV-13 filtration in residential units within 500 feet of the freeway" rather than "Improve air quality").
• Identify which recommendations can be incorporated into the proposal design, which require separate policy action, and which need ongoing monitoring.

Step 5 — Reporting and Monitoring

• Write the HIA report following the standard structure: executive summary, background, methods, assessment findings by pathway, recommendations, and monitoring plan.

• Present findings to the decision-maker within the decision timeline. An HIA that arrives after the decision is made has no influence.

• Develop a monitoring plan that specifies: which health indicators will be tracked post-decision, data sources, monitoring frequency, responsible parties, and triggers for reassessment.

• Track whether recommendations were adopted and whether predicted health impacts materialized. This evaluation feeds back into HIA practice improvement.

• Publish the completed HIA in the Health Impact Project database and relevant peer-reviewed literature.

• Evaluation of HIA effectiveness --- After the decision is made, evaluate the HIA's influence: were recommendations adopted? Did the HIA change the decision? Were predicted health impacts observed? Document lessons learned for future HIA practice in the jurisdiction.

Checkpoint B — HIA Completion Review

• Screening decision documented with rationale

• Scoping identified priority pathways with causal diagrams

• Baseline health profile completed for the affected community

• Impact estimates provided for each priority pathway with direction and magnitude

• Equity analysis conducted for all assessed impacts

• Uncertainty characterized for each impact estimate

• Recommendations are specific, actionable, and linked to findings

• Report delivered within the decision timeline

• Monitoring plan established with indicators, data sources, and responsible parties

• Health equity analysis completed for all vulnerable subpopulations

• Cumulative environmental burden assessed using CalEnviroScreen, EJScreen, or equivalent

• Post-decision evaluation plan includes HIA influence assessment

Quality Audit

• Causal pathway diagrams are evidence-based and plausible (not speculative)

• Exposure-response functions sourced from peer-reviewed literature or established models (EPA, WHO)

• Quantitative estimates include sensitivity analysis for key assumptions

• Community engagement was substantive — input influenced scoping and recommendations, not just cosmetic inclusion

• SVI or equivalent equity index applied to identify disproportionately affected populations

• Recommendations distinguish between design-phase mitigations and post-implementation monitoring

• HIA followed Minimum Elements and Practice Standards for HIA (National Academies, 2011)

• Report reviewed by multidisciplinary team (epidemiologist, environmental health specialist, community representative) before release

• Health equity analysis identifies cumulative burden on vulnerable populations using validated indices

• Quantitative methods reference peer-reviewed dose-response relationships

• Post-decision evaluation plan assesses both recommendation adoption and health outcome monitoring

• HIA report filed in the Health Impact Project database for practice advancement

Guidelines

• An HIA is advisory, not regulatory. Its power comes from evidence quality and stakeholder legitimacy, not legal authority. Frame findings accordingly.

• Timing is everything. An HIA must be completed before the decision is finalized. If the decision timeline is compressed, default to a rapid HIA rather than no HIA.

• Do not overstate quantitative precision. If the best available evidence supports only a qualitative judgment (e.g., "likely to increase respiratory symptoms"), do not fabricate a numerical estimate.

• Health equity must be central, not an appendix. Every impact pathway should be assessed for differential effects on vulnerable populations.

• Distinguish between impacts the proposal causes directly (e.g., emissions from a new facility) and impacts that are correlated but not caused by the proposal (e.g., gentrification in a neighborhood where a transit project is proposed).

• Community engagement must begin in scoping, not after the assessment is complete. Communities should help define which health issues matter, not just react to expert analysis.

• Escalate to senior public health leadership or legal counsel when: the proposal involves a known carcinogen or hazardous exposure, the decision-maker is unresponsive to health findings, or political pressure is being applied to alter assessment conclusions.

• Cumulative impact assessment is essential for environmental justice communities. A single project's air quality impact may be small, but it may be the 10th source of pollution in a community already overburdened. Use cumulative impact tools (CalEnviroScreen, EJScreen) to contextualize individual project impacts.

• Economic impacts are health impacts. Changes in employment, income, housing affordability, and displacement have well-documented effects on health outcomes. Include economic determinants in every HIA scope, not just environmental exposures.