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4. Analytical, Economic, and Evidentiary Tools

4.4. Calculating Market Shares and Concentration

This subsection further describes how the Agencies calculate market shares and concentration metrics.

As discussed above, the Agencies may use evidence about market shares and market concentration as part of their analysis. These structural measures can provide insight into the market power of firms as well as into the extent to which they compete. Although any market that is properly identified using the methods in Section 4.3 is valid, the extent to which structural measures calculated in that market are probative in any given context depends on a number of considerations. The following market considerations affect the extent to which structural measures are probative in any given context. [Endnote 92]

First, structural measures may be probative if the market used to estimate them includes the products that are the focus of the competitive concern that the structural inquiry intends to address. For example, the concentration measures discussed in Guideline 1 will be most probative about whether the merger eliminates substantial competition between the merging parties when calculated on a market that includes at least one competing product from each merging firm.

Second, the market used to estimate shares should be broad enough that it contains sufficient additional products so that a loss of competition among all the suppliers of the products in the market would lead to significantly worse terms for at least some customers of at least one product. Markets identified using the various tools in Section 4.3 can satisfy this condition—for example, all markets that satisfy the HMT do so.

Third, the competitive significance of the parties may be understated by their share when calculated on a market that is broader than needed to satisfy the considerations above, particularly when the market includes products that are more distant substitutes, either in the product or geographic dimension, for those produced by the parties.

4.4.A. Market Participants

All firms that currently supply products (or consume products, when buyers merge) in a relevant market are considered participants in that market. Vertically integrated firms are also included to the extent that their inclusion accurately reflects their competitive significance. Firms not currently supplying products in the relevant market, but that have committed to entering the market in the near future, are also considered market participants.

Firms that are not currently active in a relevant market, but that very likely would rapidly enter with direct competitive impact in the event of a small but significant change in competitive conditions, without incurring significant sunk costs, are also considered market participants. These firms are termed “rapid entrants.” Sunk costs are entry or exit costs that cannot be recovered outside a relevant market.

Entry that would take place more slowly in response to a change in competitive conditions, or that requires firms to incur significant sunk costs, is considered in Section 3.2.

Firms that are active in the relevant product market but not in the relevant geographic market may be rapid entrants. Other things equal, such firms are most likely to be rapid entrants if they are already active in geographies that are close to the geographic market. Factors such as transportation costs are important; or for services or digital goods, other factors may be important, such as language or regulation.

In markets for relatively homogeneous goods where a supplier’s ability to compete depends predominantly on its costs and its capacity, and not on other factors such as experience or reputation in the relevant market, a supplier with efficient idle capacity, or readily available “swing” capacity currently used in adjacent markets that can easily and profitably be shifted to serve the relevant market, may be a rapid entrant. However, idle capacity may be inefficient, and capacity used in adjacent markets may not be available, so a firm’s possession of idle or swing capacity alone does not make that firm a rapid entrant.

4.4.B. Market Shares

The Agencies normally calculate product market shares for all firms that currently supply products (or consume products, when buyers merge) in a relevant market, subject to the availability of data. The Agencies measure each firm’s market share using metrics that are informative about the market realities of competition in the particular market and firms’ future competitive significance. When interpreting shares based on historical data, the Agencies may consider whether significant recent or reasonably foreseeable changes to market conditions suggest that a firm’s shares overstate or understate its future competitive significance.

How market shares are calculated may further depend on the characteristics of a particular market, and on the availability of data. Moreover, multiple metrics may be informative in any particular case. For example:

  • Revenues in a relevant market often provide a readily available basis on which to compute shares and are often a good measure of attractiveness to customers.

  • Unit sales may provide a useful measure of competitive significance in cases where one unit of a low-priced product can serve as a close substitute for one unit of a higher-priced product. For example, a new, much less expensive product may have great competitive significance if it substantially erodes the revenues earned by older, higher-priced products, even if it earns relatively low revenues.

  • Revenues earned from recently acquired customers (or paid to recently acquired buyers, in the case of merging buyers) may provide a useful measure of competitive significance of firms in cases where trading partners sign long-term contracts, face switching costs, or tend to re-evaluate their relationships only occasionally.

  • Measures based on capacities or reserves may be used to calculate market shares in markets for homogeneous products where a firm’s competitive significance may derive principally from its ability and incentive to rapidly expand production in a relevant market in response to a price increase or output reduction by others in that market (or to rapidly expand its purchasing in the case of merging buyers).

  • Non-price indicators, such as number of users or frequency of use, may be useful indicators in markets where price forms a relatively small or no part of the exchange of value.


[Endnote 92] For simplicity, the discussion in the text focuses on the case where concerns arise that involve competition among the suppliers of products; analogous considerations may also arise for suppliers of services, or when concerns arise about competition among buyers of a product or service, or when analyzing market shares in certain specific settings (see Section 4.3.D).