Case Study—How can we build fairness into automated systems, and what evidence is needed to do so? Recently, Airbnb grappled with this question to brainstorm ways to re-envision the way hosts review guests who stay with them. Reviews are key to how Airbnb builds trust between strangers. In 2018 we started to think about new ways to leverage host reviews for decision making at scale, such as identifying exceptional guests for a potential loyalty program or notifying guests that need to be warned about poor behavior. The challenge is that the evidence available to use for automated decisions, star ratings and reviews left by hosts, are inherently subjective and sensitive to the cross-cultural contexts in which they were created. This case study explores how the collaboration between research and data science revealed that the underlying constraint for Airbnb to leverage subjective evidence is a fundamental difference between ‘public’ and ‘private’ feedback. The outcome of this integrated,...