Contact Tracing Technologies: Methods and trade-offs

Alex Berke

Alex Berke and Kent Larson, City Science group, MIT Media Lab (2020).


Many organizations are working on technology for contact tracing, and the landscape is changing rapidly. This is an overview of existing contact tracing technologies, along with different methods and trade-offs to consider when building new ones. 

Governments around the world are considering the deployment of contact tracing technologies to help contain the spread of COVID-19 and mitigate its economic impacts. Combined with increased testing, effective contact tracing offers the opportunity to improve policy decisions by providing information to help safely re-open economies and intervene only when new outbreaks are detected. In particular, governments and communities may use contact tracing technology to:
• Target quarantines to mitigate the economic impacts of stay-at-home orders
• Understand transmission trends
• Better use limited testing resources
• Conduct targeted serology testing in order to expedite the return of a workforce
• Improve traditional labor-intensive contract tracing efforts 

However, it is not yet known whether contact tracing technologies will have the impact so many of us desire. They will need to be widely adopted and accurate in order to be effective, and they will need to provide enough information about their users to health authorities or governments in order to guide future policy decisions. These challenges raise both technical issues and societal issues, as deploying effective contact tracing technologies may jeopardize individual privacy rights and freedoms. 

There are many ways contact tracing technologies can be designed, but each design decision leads to different trade-offs between their potential accuracy, adoption, usefulness, and privacy risks. This white paper explains these differences and trade-offs and raises questions to be addressed by the builders of these technologies and the communities who use them. It is important that the public understand how contact tracing systems function and what their alternatives are because their widespread adoption may drastically impact our privacy and change how we move or work in public. 

We begin with an explanation of how existing contact tracing technologies work and how future alternatives might work instead so that their trade-offs may be better evaluated. In particular, we cover differences in how data is sourced and used to detect contacts, whether the flow of information is centralized or decentralized, how COVID-positive cases are reported, how exposure risk is assessed and how the system’s users are impacted. We then discuss how these differences lead to trade-offs between accuracy, adoption, usefulness and privacy. 

Our goal is to leave you informed and to also raise critical questions as to whether any of these technologies can be useful enough to be worth their trade-offs for potential benefits that cannot yet be measured.

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