At a glance
The CDC/ATSDR Social Vulnerability Index (CDC/ATSDR SVI or SVI) is a place-based index, database, and mapping application designed to identify and quantify communities experiencing social vulnerability. The Geospatial Research, Analysis & Services Program (GRASP) maintains the SVI to help public health officials and local planners better prepare for and respond to emergency events with the goal of decreasing human suffering, economic loss, and health inequities. Learn more about the SVI in the frequently asked questions below.
How can I find documentation that defines the variables in the CDC/ATSDR SVI?
Documentation for all versions of the SVI can be found on our Data & Documentation Download page. Within the documentation, there is a data dictionary that contains information for each SVI variable, including the variable name, description, where we obtained the data, and how the variable was calculated.
Which CDC/ATSDR SVI ranking variables should I be using?
The CDC/ATSDR SVI ranking variables for the four themes are:
- RPL_THEME1 for the Socioeconomic Status theme
- RPL_THEME2 for the Household Characteristics theme
- RPL_THEME3 for the Racial & Ethnic Minority Status theme
- RPL_THEME4 for the Housing Type & Transportation theme.
RPL_THEMES is the SVI ranking variable for overall vulnerability. See the CDC/ASTDR SVI Documentation for further information.
How do I interpret the CDC/ATSDR SVI ranking for a census tract (or county)?
A percentile ranking represents the proportion of tracts (or counties) that are equal to or lower than a tract (or county) of interest in terms of social vulnerability. For example, a CDC/ATSDR SVI ranking of 0.85 signifies that 85% of tracts (or counties) in the state or nation are less vulnerable than the tract (or county) of interest and that 15% of tracts (or counties) in the state or nation are more vulnerable.
How are the CDC/ATSDR SVI variables and themes weighted?
All the variables are weighted equally, as are the four theme rankings. We do this to provide a simple, easy to understand approach to the methodology. However, we encourage the SVI to be tailored based on local knowledge, so users may add weights as they see fit.
What do the symbology values in the CDC/ATSDR SVI Interactive Map represent?
In the SVI Interactive Map, we classify data using quartiles (0 to 0.2500, 0.2501 to 0.5000, 0.5001 to 0.7500, 0.7501 to 1.0) and indicate that the classification goes from least vulnerable to most vulnerable. While we do not have required cutoffs for working with SVI data, as the SVI data are relative rankings and scored from 0-1, categorizing SVI values using a quantile classification (i.e., tertiles, quartiles, quintiles, etc.) is a common approach. If you choose to categorize CDC/ATSDR SVI values, we recommend you do so appropriately based on your question of interest.
What is the difference between the U.S.-based and state-based CDC/ATSDR SVI databases?
The U.S.-based SVI database compares the social vulnerability of a census tract (or county) to all tracts (or counties) in the United States. The state-based SVI database compares the social vulnerability of a census tract (or county) solely to tracts (or counties) within a particular state of interest.
How frequently is the CDC/ATSDR SVI updated?
The SVI is updated every two years based on U.S. Census Bureau data releases. The Census usually releases American Community Survey data in December of the year following the Survey. Thus, there is a time differential in when we can produce and disseminate updates to the SVI.
Are CDC/ATSDR SVI rankings available at the ZIP code or ZIP code tabulation area (ZCTA) level?
ZIP codes are postal delivery routes, which lack defined borders and are subject to change by the U.S. Postal Service. While ZIP code enumeration may change frequently, U.S. Census Bureau ZCTAs are relatively stable areal representations of ZIP codes for a snapshot of time. Persons interested in using ZIP code levels may benefit from incorporating HUD USPS ZIP Code Crosswalk Files or by using ZCTA files from the American Community Survey to recreate the CDC/ATSDR SVI.
How do I find CDC/ATSDR SVI rankings for U.S. territories?
We provide SVI data for Puerto Rico, which is not included in the U.S.-wide SVI database. These data for Puerto Rico are ranked separately from U.S. states in a stand-alone Puerto Rico-specific SVI database. However, this is the only U.S. territory for which we produce SVI because sociodemographic census variables for the other territories (Guam, American Samoa, the U.S. Virgin Islands, the North Mariana Islands) are unavailable in the American Community Survey.
Does the CDC/ATSDR SVI have information about Tribal areas?
Starting with the 2014 version of the SVI, we provide SVI data for tribal census tracts. The tribal tract database is a stand-alone database that contains only estimates, percentages (and their respective margins of error (MOEs)), and the adjunct variables. Because of geographic separation and cultural diversity, tribal tracts are not ranked against each other nor against standard census tracts.
How can I get more information about the CDC/ATSDR SVI?
For more information, please visit the CDC/ATSDR SVI homepage or contact the CDC/ATSDR SVI Coordinator.