Google COVID-19 Community Mobility Reports: Anonymization Process Description (version 1.1)

TL;DR

This paper details the anonymization process used in Google's COVID-19 mobility reports to protect individual privacy while providing useful data for public health decision-making during the pandemic.

Contribution

It introduces a specific anonymization and aggregation methodology ensuring privacy in publicly released mobility data during COVID-19.

Findings

Effective anonymization of mobility data

Reliable percentage change metrics generated

Public health insights enabled

Abstract

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.