Decision theory combines probability theory with utility theory and provides a formal and complete framework for decisions (economic or otherwise) that are made under uncertainty – that is, in cases where probabilistic descriptions appropriately capture the decision maker’s environment.

This is suitable for “large” economies where each agent need pay no attention to the actions of other agents as individuals. For “small” economies, the situation is much more like a game: the actions of one player can significantly affect the utility of another (either positively or negatively).