DOI: 10.57761/dm1c-cn09
title: CalEnviroScreen

description: CalEnviroScreen identifies California communities by census tract that are disproportionately burdened by, and vulnerable to, multiple sources of pollution.
description: #Documentation  
CalEnviroScreen uses a science-based method for evaluating multiple pollution sources in a community while accounting for a community’s vulnerability to pollution’s adverse effects. These data are used to identify disadvantaged communicates and allocate resources and decide policies.

Using multiple sources of data, CalEnviroScreen is a tool that produces

- a relative, rather than absolute, measure of pollution’s impacts and vulnerabilities in California communities.
- Provide a consistent assessment and methodology with prior versions of the tool, that has been expanded and updated with additional information.
-  Evaluate multiple pollution sources, and stressors that measure a community’s vulnerability to pollution.

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**Method**

**The CalEnviroScreen model**

- Uses a suite of statewide indicators to characterize both Pollution Burden and Population Characteristics
- Uses a limited set of indicators in order to keep the model simple.
- Uses percentiles to assign scores for each of the indicators in a given geographic area. The percentile represents a relative score for the indicators.
- Uses a scoring system in which the percentiles are averaged for the set of indicators in each of the four components (Exposures, Environmental Effects, Sensitive Populations, and Socioeconomic Factors).
-  Combines the component scores to produce a CalEnviroScreen score for a given place relative to other places in the state, using the formula below. 

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Most data are averages between 2012-2014 or single year measurements around the same time. After the components are scored within Pollution Burden or Population Characteristics, the scores are combined as follows to calculate the overall CalEnviroScreen Score:



![calenviroscreenscore](<https://redivis.com/fileUploads/6fe39054-2311-4a76-9c1c-1190b71f0bc0>)**Formula for CalEnviroScreen scores**

The mathematical formula for calculating scores uses multiplication. Scores for the pollution burden and population characteristics categories are multiplied together (rather than added, for example). Although this approach may be less intuitive than simple addition, there is scientific support for this approach to scoring. Multiplication was selected for the following reasons:

1. Scientific Literature: Existing research on environmental pollutants and health risk has consistently identified socioeconomic and sensitivity factors as “effect modifiers.” For example, numerous studies on the health effects of particulate air pollution have found that low socioeconomic status is associated with about a 3-fold increased risk of morbidity or mortality for a given level of particulate pollution (Samet and White, 2004). Similarly, a study of asthmatics found that their sensitivity to an air pollutant was up to 7-fold greater than non-asthmatics (Horstman et al., 1986). Low-socioeconomic status African-American mothers exposed to traffic-related air pollution were twice as likely to deliver preterm babies (Ponce et al., 2005). The young can be 10 times more sensitive to environmental carcinogen exposures than adults (OEHHA, 2009). Studies of increased risk in vulnerable populations can often be described by effect modifiers that amplify the risk. This research suggests that the use of multiplication makes sense. 2. Risk Assessment Principles: Some people (such as children) may be 10 times more sensitive to some 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 (US EPA, 2012). 3. Established Risk Scoring Systems: Priority-rankings done by various emergency response organizations to score threats have used scoring systems with the formula: Risk = Threat × Vulnerability (Brody et al., 2012). These formulas are widely used and accepted. 

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The maximum scores for combined components is:



![max score.png](<https://redivis.com/fileUploads/166b9940-4a97-4b57-9f04-c9c4665227fb>)**Notes on Scoring System**

In the CalEnviroScreen model, the Population Characteristics are a modifier of the Pollution Burden. In mathematical terms, the Pollution Burden is the multiplicand and Population Characteristics is the multiplier, with the CalEnviroScreen Score as the product. The final ordering of the communities is independent of the magnitude of the scale chosen for the Population Characteristics (without rounding scores). That is, the communities would be ordered the same in their final score if the Population Characteristics were scaled to 3, 5, or 10, for example. Here, a scale up to 10 was chosen for convenience.



**Selection of Geographic Scale**

CalEnviroScreen 3.0 uses the census tract scale as the unit of analysis. Census tract boundaries are available from the Census Bureau. These were updated in 2010. There are approximately 8,000 census tracts in California, representing a relatively fine scale of analysis. Census tracts are made up of multiple census blocks, which are the smallest geographic unit for which population data are available. Some census blocks have no people residing in them (unpopulated blocks).



**Description of Zero's and Missing Values**

8035 California Census Tracts are used in the CalEnviroScreen analysis



![zero_na.png](<https://redivis.com/fileUploads/ed7c2afa-1d51-4e16-9d6d-c861da58e9bc>)**What do indicator raw values of zero and NA mean?**

- NA or missing raw values: When an indicator has a missing value (“NA”), it typically means no monitoring or reporting was conducted or no population was reported within that census tract. For example, ambient air quality measures are not available for all California census tracts because many places do not have an air monitor close enough to reliably estimate air quality in that community. There are 11 out of 8035 census tracts that have zero population reported by the U.S. Census. These were assigned “NA” for all population characteristic indicators. In addition, census tracts with highly unreliable estimates for the educational attainment, linguistic isolation, poverty, and rent-adjusted income indicators were assigned “NA.” These variables are derived from the household data rather than individual level data (see the report for more detail). 

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- Zero raw values: A value of zero, typically implies that monitoring or reporting was conducted, but no impacts were present. For many exposure and environmental effects indicators, this means that no facilities or sites were located within 1000 meters of a populated area of the census tract. For example, 2553 census tracts did not have a Cleanup site within 1000 meters of a populated area of the census tract. These census tracts were given a value zero. Similarly, a zero for a Population Characteristics indicator such as poverty, for example, means people live there but there are no residents under the poverty level. 

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**What do percentiles of zero and NA mean?**

- NA or missing percentiles values: Indicators that include missing values (“NA”) are PM 2.5, Traffic, Drinking Water, Low Birth Weight and all socioeconomic factor indicators. In these cases, missing values were assigned no percentile (given an “NA”) and did not contribute to their overall CalEnviroScreen score. For example, if a census tract was missing both and PM2.5 and Traffic the denominator of the exposure indicators was adjusted to five instead of seven indicators. 

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- Zero percentile values: Many census tracts for exposure and environmental effects indicators have a raw value of zero. We do not include these census tracts in the percentile calculation, which would give the false impression that an impact is present. For example, around 64% of census tracts have none of the select pesticides used. If these were used in the percentile calculation, a value of zero would correspond to the 63rd percentile. It is more appropriate to assign these places a percentile value of “0” corresponding to no impact. This means that for the pesticide indicator, 2888 (8035 minus 5147) census tracts make up the percentile range. Indicators with missing values (“NAs”) are never included in the percentile calculation. The Education indicator has 7926 census tracts in the percentile calculation (8035 minus 13 (zeros values) minus 96 (missing values) = 7926).

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**More information**

[Website](<https://oehha.ca.gov/calenviroscreen/report/calenviroscreen-30>)

[Report](<https://oehha.ca.gov/media/downloads/calenviroscreen/report/ces3report.pdf>)