have used these guidelines to convince courts to adopt a more explicitly economic approach to antitrust policy. A relevant market comprises a product or group of products and the geographic area in which these products are produced and/or traded. Therefore, the relevant market has two components: the product market and the geographic market. Product market The relevant product market is determined according to three criteria: Demand-side substitution. Supply-side substitution. Potential competition. Demand-side substitution Demand-side substitution takes place when consumers switch from one product to another in response to a change in the relative prices of the products. If consumers are in a position to switch to available substitute products or to begin sourcing their requirements from suppliers located in other areas, then it is unlikely that price increases will be profitable. Therefore, it is necessary to progressively include in the relevant market the products to which consumers would most likely switch in response to a relative price rise, repeating the exercise at each stage until a collection of products is reached that is worth monopolising. When examining the likely responses of consumers, it is the response of the marginal consumer, not the average consumer which is important. Therefore, a small but significant number of consumers (generally 5 to 10 percent) switching to another product when there is a price increase is considered a sufficient condition for both goods to be defined as forming part of the same relevant market. Therefore, the existence of a group of consumers who would never switch in response to a relative price increase is not by itself sufficient to conclude that the relevant market should be defined narrowly. Determining both the likely extent of demand-side substitution, and the level of substitution which would imply that monopolisation was not worthwhile, requires an assessment of the price-elasticity of demand. This is generally done using the SSNIP-test. However, in digital markets, where consumers are often offered services for free, the SSNIP test cannot be performed, being the price equal to zero. For this reason, different techniques (including machine learning) are employed to define the relevant market. Supply-side substitution Sometimes consumers may be unable to react to a price increase, nevertheless, producers may be able to do so by for example, increasing their supply to satisfy the demand of these consumers. If other producers respond to an increase in the relative price of the products supplied by the single