The overcharge has a one-to-one relationship to the Lerner Index, the most common measure of market power in economics. Both measures employ the same numerator (PM - PC), where PM is the observed market price and PC is the competitive benchmark price, but use different denominators. The overcharge ratio is (PM-PC)/PC, whereas the Lerner Index is (PM-PC)/PM. Both ratios are zero when a market is perfectly competitive or a cartel is ineffective in raising prices. The Lerner Index has an upper limit of one when the pure monopoly price is charged in a market. The overcharge has no upper limit.