Given a contest between two opponents where it is unknown who is favored, how many games must be plays to reach a given level of confidence in who is favored?
For example, Player A and Player B can play a game and determine a winner. There is a certain probability of Player A winning, which we would have a pretty good idea of if they played 1,000,000 games. They start playing. Player A wins three games and Player B wins one. The actual win % of Player A is 75%, but the game could easily be a coin flip and we're just seeing variance. How many games would take to have 90% confident that the overall win % approaches a single number?