What Differential Privacy in the 2020 Decennial Census Means for Researchers:
Anonymous | October 8, 2022
Federal Law mandates that the United States Census records must remain confidential for 72 years, but they’re also required to release statistics for social science researchers, businesses, and local governments. The Census has tried many options for releasing granular statistics while protecting privacy, and for the 2020 Census they’re utilizing Differential Privacy (Ruggles, 2022). The most granular data that the Census will publish is its block level data – which in some cases is actual city blocks but in others is just a small region. To protect individual identities within each block, Differential Privacy will add noise to the statistics produced. This noise has caused concern for researchers and people using the data. This post is about how to spot some of the noise, and how to work with the data knowing that there is going to be noise.
Noise from differential privacy should impact low population blocks and subsets of people – such as minority groups who will have low population counts (Garfinkel, 2018). In the block level data, this is obvious in some blocks that shouldn’t have any people, or have people but no households (Wines, 2022). Block 1002 is in downtown Chicago and consists of just a bend in the river, the census says that 14 people live there. There are no homes there, so it’s obvious that these people are a result of noise from Differential Privacy. Noise like this might concern data scientists, but it should affect most statistical analyses like forms of outlier control or post-processing (Boyd, 2022). It shouldn’t negatively impact most research. So if you spot noise, don’t worry, it’s an error (purposefully).
The noise produced by Differential Privacy does affect research done on groups with small populations though. Individuals in small population groups, like Native American Tribes, are more easily identified in aggregate statistics so their stats will receive more noise to protect their identities noise (National Congress of American Indians, 2021). For these reasons, researchers at the National Congress of American Indians and the Alaska Federation of Natives have asked the Census for ways to access the unmodified statistics. Their work often requires having precise measurements of small population groups that are known to be heavily impacted by noise (National Congress of American Indians, 2021). If you think that this might impact your research, consult with an expert in Differential Privacy regarding your research.
The Census’ Differential Privacy implementation should improve privacy protection without impacting research results substantially. Attentive scientists will still find irregularities in the data, and some studies will be difficult to complete with the Differentially Private results, so it is important to understand how Differential Privacy has impacted the dataset.
Sources:
Boyd, Danah and Sarathy, Jayshree, Differential Perspectives: Epistemic Disconnects Surrounding the US Census Bureau’s Use of Differential Privacy (March 15, 2022). Harvard Data Science Review (Forthcoming). Available at SSRN: https://ssrn.com/abstract=4077426
National Congress of American Indians. “Differential Privacy and the 2020 Census: A Guide to the Data and Impacts on American Indian/Alaska Native Tribal Nations.” National Congress of American Indians Policy Research Center. May 2021.
Ruggles, Steven, et al. “Differential Privacy and Census Data: Implications for Social and Economic Research.” AEA Papers and Proceedings, vol. 109, 2019, pp. 403–08. JSTOR, https://www.jstor.org/stable/26723980. Accessed 7 Oct. 2022.
Simson L. Garfinkel, John M. Abowd, and Sarah Powazek. “Issues Encountered Deploying Differential Privacy.” In Proceedings of the 2018 Workshop on Privacy in the Electronic Society (WPES’18). Association for Computing Machinery, New York, NY, USA, pages 133–137. 2018. https://doi-org.libproxy.berkeley.edu/10.1145/3267323.3268949
Wines, Michael. “The 2020 Census Suggests That People Live Underwater. There’s a Reason.” New York Times. April 21st, 2022. https://www.nytimes.com/2022/04/21/us/census-data-privacy-concerns.html