CDC/ATSDR SVI: Frequently Asked Questions (FAQ)

Español (Spanish)

The CDC/ATSDR Social Vulnerability Index (CDC/ATSDR 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 CDC/ATSDR 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 CDC/ATSDR SVI in the frequently asked questions and responses below.

Documentation for all versions of the CDC/ATSDR SVI can be found on our Data & Documentation Download page. Within the documentation, there is a data dictionary that contains information for each CDC/ATSDR SVI variable, including the variable name, description, where we obtained the data, and how the variable was calculated.

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 CDC/ATSDR SVI ranking variable for overall vulnerability. See the CDC/ASTDR SVI Documentation for further information.

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.

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 CDC/ATSDR SVI to be tailored based on local knowledge, so users may add weights as they see fit.

In the CDC/ATSDR 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 CDC/ATSDR SVI data, as the CDC/ATSDR SVI data are relative rankings and scored from 0-1, categorizing CDC/ATSDR 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.

The U.S.-based CDC/ATSDR SVI database compares the social vulnerability of a census tract (or county) to all tracts (or counties) in the United States. The state-based CDC/ATSDR SVI database compares the social vulnerability of a census tract (or county) solely to tracts (or counties) within a particular state of interest.

The CDC/ATSDR 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 CDC/ATSDR SVI.

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.

We provide CDC/ATSDR SVI for Puerto Rico, which is not included in the U.S.-wide CDC/ATSDR SVI database. These data for Puerto Rico are ranked separately from U.S. states in a stand-alone Puerto Rico-specific CDC/ATSDR SVI database. However, this is the only U.S. territory for which we produce CDC/ATSDR 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.

Starting with the 2014 version of CDC/ATSDR SVI, we provide CDC/ATSDR 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.

For more information, please visit the CDC/ATSDR SVI homepage or contact the CDC/ATSDR SVI Coordinator.

Questions or Comments? Contact the CDC/ATSDR SVI Coordinator (svi_coordinator@cdc.gov).