From what I can tell, everyone just gets as much ELO as points scored during a game. Also, since this is a cooperative game that you cannot lose, there's no way to lose ELO as well. So if you just play this all the time, you'll have a really high ELO rating as well. Ironically, when I playing this yesterday, the guy with 10 times as much ELO as everyone else gave the worst clues.