An index of competitiveness and cooperativeness for normal-form games

We develop an index of competitiveness and cooperativeness which is based on the primitives of a normal-form game, i.e., players, strategies and payoffs. The index relies on the unique decomposition of a given game into a zero-sum game and a common-interest game. The index decreases in the distance to its zero-sum part and it increases in the distance to its common-interest part. The comparative statics of our index coincide with economic intuition. The index also supports experimental findings in well-known classes of games in the sense that more cooperative and less competitive behavior correlates with lower values of the index.