A new way to measure competition

This article introduces a new way to measure competition based on firms' profits. Within a general model, we derive conditions under which this measure is monotone in competition, where competition can be intensified both through a fall in entry barriers and through more aggressive interaction between players. The measure is shown to be more robust theoretically than the price cost margin. This allows for an empirical test of the problems associated with the price cost margin as a measure of competition.