Census Bureau Announces Traditional Redistricting Data Not Recommended for Use This Decade

By Christi Zamarripa and Ben Williams

The Census Bureau released a blog yesterday describing what the redistricting data will look like when it is released in three weeks. It will reflect the demographic changes and shifts that normally occur every 10 years, but will also show the effects of the COVID-19 pandemic and differential privacy.

As NCSL has previously highlighted, the 2020 Census redistricting data will be protected by differential privacy. This privacy protection method involves injecting 'noise,' or a degree of error, into the census numbers to help protect the confidentiality of respondents.

Dr. Jarmin, acting director of the Census Bureau, discussed how this 'noise' will make census blocks look 'fuzzy,' or inaccurate. Therefore, data users may notice situations like the following:

• Occupancy status doesn't match population counts. Some blocks may show that the housing units are all occupied, but the population count is zero. Other blocks may show the reverse: The housing units are vacant, but the population count is greater than zero.
• Children appear to live alone. Some blocks may show a population count for people younger than 18 but show no people age 18 and older.
• Households appear unusually large. For example, you may find blocks with 45 people, but only three housing units.

The Census Bureau 'strongly encourage(s) data users to aggregate, or group, blocks together' because the 'new privacy protections may make the data at the lowest geographies look slightly different.'

This will require 'a shift in how some data users typically approach using these census data,' according to the bureau. There may be a need to combine these 'fuzzy' blocks into group blocks to form sharper pictures of census tracts, cities, voting districts, counties and other areas.

Redistricting data will be released to the public in less than three weeks, on Aug. 16. With so little time left, the bureau is very unlikely to make changes that could improve accuracy at the block level. It's important to know what is expected when it does get released and not be surprised-and NCSL will be there every step of the way to ensure states are well-prepared for what comes next.

Christi Zamarripa is a policy associate and Ben Williams is a policy specialist in NCSL's Elections and Redistricting Program.

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