- Aligned incentives. The skill rating system should create incentives that align with the spirit of the game. For example, consider a team game where players cooperate to achieve a goal. An improperly-designed skill rating system could encourage players to impede their teammates. As another example, consider a system that increased skill rating according to the number of times a player healed themselves. This creates an incentive for a player to repeatedly injure themselves so that they could be healed. In general, the more control that a player has over a quantity, the less useful it is for skill rating. — this is from Microsoft research