A computer system includes a server computer that handles transactions with user devices to create and manage events, create and manage user accounts and process wagers. Transactions regarding wagers in connection with events can be processed in real-time. The wagers are processed using a payoff function that rewards participation and accurate information, yet does not permit arbitrage or otherwise reward splitting a wager by participating under multiple identities. To compute a payoff, a first score is computed based on the probability estimate by a participant and the outcome. A second score is computed based on an aggregate of wagers of all other participants for each participant, where the first score for the participant is no more than the second score for at least one outcome. The payoff for the participant is then computed as a function of the first score and the second score.