The Unexpected Downside of Paying or Sending Messages to People to Make Them Walk: Comparing Tangible Rewards and Motivational Messages to Improve Physical Activity. - CHERUBINI, MAURO; VILLALOBOS-ZUÑIGA, GABRIELA; BOLDI, MARC-OLIVIER; BONAZZI, RICCARDO (ACM Transactions on Computer-Human Interaction (TOCHI), 2020)