The correct answer is: D. None of the above
The Learner index is a measure of the extent to which a firm is able to learn from its own experience and that of its rivals. It is calculated as the ratio of the firm’s current costs to the costs of a hypothetical firm that has the same production technology but has never made any mistakes. A higher Learner index indicates that the firm is learning more quickly and is therefore more likely to be successful in the long run.
Market power is the ability of a firm to raise prices above marginal cost without losing all of its customers. Price is the amount of money that a buyer pays for a good or service. Price-marginal cost is the ratio of price to marginal cost.
Market power, price, and price-marginal cost are all important concepts in economics, but they are not what the Learner index measures. The Learner index is a measure of a firm’s ability to learn from its own experience and that of its rivals.