1. What is a cumulative impact assessment, and how does it compare to a risk assessment?
CalEnviroScreen looks at the impacts of pollution in communities by analyzing “factors that are not routinely included” in a risk assessment.  While the terms risk and impact are often perceived as synonyms, they don’t have the same meaning. The term risk means a probability of an injury or loss, while impact in this context refers more broadly to stressors that can affect health and quality of life. 164 A cumulative impact assessment does not provide a quantitative approach to evaluating harm, but rather integrates quantitative factors with “others that may increase the magnitude of adverse effects” but are more difficult to measure or estimate. 
The cumulative impact assessment methodology used in CalEnviroScreen is based on several scientific principles:
- Scientific research demonstrates that socioeconomic and other “sensitivity factors” are “effect modifiers” that can increase health risk by factors ranging from threefold to tenfold or greater, depending on the combination of pollutants and underlying susceptibilities. 
- Some members of the population (such as children or those with underlying health conditions) may be 10 times more sensitive to certain chemical exposures than others. “Risk assessments, using principles first advanced by the National Academy of Sciences, apply numerical factors or multipliers to account for potential human sensitivity (as well as other factors such as data gaps) in deriving acceptable exposure levels.” 
- Various emergency response organizations have scored threats using the formula: “Risk = Threat × Vulnerability.” 
2. What is the formula for determining the final or overall CalEnviroScreen score?
The data for each of the 20 indicators is calculated into a raw score and assigned a percentile ranking. The indicator percentiles are then averaged to calculate the Pollution Burden and Population Burden scores. (Environmental effects receive less weight because they measure the general “presence of pollutants in the community,” not community exposures.) The two scores are then scaled and multiplied to derive the overall CalEnviroScreen score, expressed as a percentile ranking. 
After the components are scored within Pollution Burden or Population Characteristics, the scores are combined as follows to calculate the overall CalEnviroScreen Score:
3. Why does CalEnviroScreen 3.0 use census tracts rather other geographical units such as ZIP codes or census blocks?
California’s approximately 8,000 census tracts represent a “relatively fine scale of analysis.” 170 Each census tract is further broken down into multiple census blocks. Scores are not calculated at the census block level, however, because some census blocks are unpopulated. Previous versions of CalEnviroScreen used ZIP codes as the unit of analysis. Although ZIP codes may be easier for the public to understand, there are only about 1,800 in California. In addition, census tracts: (1) have “more demographic data” available; (2) “are, on average, more uniform in population than ZIP codes”; and (3) “do not cross county boundaries, while ZIP codes frequently do.” 
4. How is CalEnviroScreen 3.0 different from CalEnviroScreen 2.0?
CalEnviroScreen 3.0 has been updated to include the most recent data for each indicator and includes improvements for how some indicators are calculated. Detailed information about the updates is available here: https://oehha.ca.gov/ media/downloads/calenviroscreen/document/ces3newinces3.pdf.
Changes to CES 3.0 from version 2.0 include: 
- Addition of two new indicators: Cardiovascular Disease, a “health vulnerability indicator,” andHousing Burden, a socioeconomic indicator that addresses “differences in housing costs across the state.” 
- An updated scoring method to balance the “contributions of the four major components of the CalEnviroScreen score.” 
- Removal of the “Age: Children and Elderly”indicator because it did not accurately measure the most vulnerable children and elderly across the state. Instead, children and elderly are highlighted in a separate analysis that includes demographic data, including race, for each census tract. “Excluding the Age indicator did not result in significant changes in the percent children, elderly, and different racial/ethnic groups of the most highly scoring census tracts.” 
- Additional data on several indicators for communities in the California-Mexico border region. The border-related changes are described here: https://oehha.ca.gov/calenviroscreen/report/ calenviroscreen-data-update-border-region
5. What is OEHHA’s process for updating CalEnviroScreen?
CalEPA and OEHHA have both demonstrated a commitment to incorporating public feedback during the ongoing process to update the CalEnviroScreen tool over time. As a result, the CalEnviroScreen tool has been improved to more accurately capture disadvantaged communities across the state in each version. Both CalEPA and OEHHA are open to receiving relevant research and suggestions for refining CalEnviroScreen. Before each version is finalized, OEHHA releases a draft version of the tool, holds public workshops across the state, and opens up a comment period to accept public comments. CalEPA and OEHHA aim to provide regular updates of the tool in order to make needed improve- ments and include the most current pollution and demographic data; however, the state Legislature may also direct OEHHA to initiate updates. For instance, the creation of CES 3.0 was partially motivated by the passage of AB 1059 (E. Garcia, 2015), which required OEHHA to incorporate pollution data for the areas along the U.S.-Mexico border upon the next update to CalEnviroScreen.
163. Update to the California Communities Environmental Health Screening Tool, CalEnviroScreen 3.0. https://oehha.ca.gov/media/ downloads/calenviroscreen/report/ces3report. pdf p. 2.
166. Update to the California Communities Environmental Health Screening Tool, CalEnviroScreen 3.0 (CES 3.0) report. Retrieved at: https://oehha.ca.gov/media/downloads/ calenviroscreen/report/ces3report.pdf (pp. 6–7).
169. Id. at pp. 13-14. 170. Id. atp.8.
- OEHHA. Major Changes in CalEnviroScreen 2.0. https://oehha.ca.gov/media/ CES20SummaryMajorChanges.pdf.
- OEHHA. New in CalEnviroScreen 2.0, Changes Since Version 2.0. https://oehha.ca.gov/ media/downloads/calenviroscreen/document/ ces3newinces3.pdf.
- CES 3.0, p. 3.
- https://oehha.ca.gov/media/downloads/ calenviroscreen/report/ces3report.pdf.