Google COVID-19 Community Mobility Reports: Anonymization Process Description (version 1.1)
This provides a publicly available resource to help public health authorities understand mobility trends during the COVID-19 pandemic, but it is incremental as it focuses on describing an existing process.
The paper describes the anonymization process for Google COVID-19 Community Mobility Reports, which aggregates and anonymizes location data from opted-in users to provide public metrics on mobility changes during the COVID-19 pandemic, ensuring no personal data can be derived.
This document describes the aggregation and anonymization process applied to the initial version of Google COVID-19 Community Mobility Reports (published at http://google.com/covid19/mobility on April 2, 2020), a publicly available resource intended to help public health authorities understand what has changed in response to work-from-home, shelter-in-place, and other recommended policies aimed at flattening the curve of the COVID-19 pandemic. Our anonymization process is designed to ensure that no personal data, including an individual's location, movement, or contacts, can be derived from the resulting metrics. The high-level description of the procedure is as follows: we first generate a set of anonymized metrics from the data of Google users who opted in to Location History. Then, we compute percentage changes of these metrics from a baseline based on the historical part of the anonymized metrics. We then discard a subset which does not meet our bar for statistical reliability, and release the rest publicly in a format that compares the result to the private baseline.