Which of the following measures market power? a

The correct answer is option D: Lerner index

The Lerner Index is a measure of market power in an industry. It measures the price-cost margin which is derived from the difference between the output price of a firm and the marginal cost divided by the output price.

Rothchild index is a measure of the difference between price and marginal cost as a fraction of the product's price. It calculates the percentage markup that a firm can charge over its minimal cost

The Herfindahl Hirschman Index is a measurement used to understand the level of competition that exists within an industry while indicating how the distribution of market share occurs across the companies included in the index.