Market Definition in Antitrust: The SSNIP Test Explained

Many digital platforms have zero prices, making the SSNIP test inapplicable since a 5-10% increase on zero remains zero. Proposed solutions include the SSMDQ (Small but Significant Non-Transitory Decrease in Quality) test, which degrades an aspect of product quality to observe substitution effects. However, determining standard quality measures across heterogeneous markets is difficult. Another approach involves assessing service functionalities to identify close substitutes, though this lacks the rigor of the SSNIP test.

The SSNIP (Small but Significant and Non-transitory Increase in Price) test, also known as the hypothetical monopolist test, is a method for defining relevant markets by starting with a narrow market definition and asking whether a 5-10% price increase would be profitable for a hypothetical monopolist; if yes, that defines the relevant market, while if not, the market is broadened to include closer substitutes until monopolistic pricing becomes profitable, with key considerations including the distinction between product markets (substitutable goods) and geographic markets (same product at different locations), along with limitations such as the arbitrary nature of the 5-10% threshold, measurement challenges, and the 'cellophane fallacy' where existing monopolistic pricing leads to overly broad market definitions.

Even when prices are zero, firms may possess significant market power on non-price dimensions such as quality and privacy. Traditional SNIP tests may not work well in these cases, but this doesn't mean markets cannot be analyzed. Authorities need to identify competitive constraints and recognize that significant degradations in quality or privacy could impact consumer welfare even without observable price changes.

An extended version of the SSNIP (Small but Significant Non-transitory Increase in Price) test is conducted to define relevant markets. The analysis examines whether categories in Google Play can constitute antitrust-relevant markets. Results show that game categories such as action games, puzzle games, and role-playing games can form antitrust-relevant markets, while none of the non-game categories can form such markets.

Merger simulations incorporating strategic competitor responses validate SSNIP test results. When checking if categories form relevant markets, merger simulations show damage to consumer surplus is pronounced only in categories where SSNIP test identified them as relevant markets. This validates using SSNIP test as a convenient screening device for potentially anti-competitive mergers.

Economic analysis is central to merger regulation, serving as the analytical framework within a legal framework; effective merger review requires economists to work collaboratively with lawyers, using a combination of quantitative techniques (descriptive statistics, critical loss analysis, price concentration regressions, and merger simulation) and qualitative analysis (document review, witness interviews) to assess potential anti-competitive effects such as unilateral effects, coordinated effects, vertical and conglomerate effects, while recognizing that merger review is inherently forward-looking and requires careful consideration of counterfactual scenarios and the trade-off between competition concerns and potential efficiency gains.

Merger simulation results from the Unilever-Sara Lee case showed Dove and Sunnex prices increased by 10-20% in Belgium, Netherlands, and UK markets. The European Commission approved the merger subject to divestment of Sunnex to an independent company, eliminating competitive concerns. The SSNIP test (Small but Significant Non-transitory Increase in Prices) determines relevant markets by checking if hypothetical monopolization would raise prices by more than 5%. This test revealed male and non-male deodorant markets in each country were separate relevant markets, not a single unified market.

For demand-side substitution analysis, authorities consider: (1) The SSNIP test (even conceptually), (2) Information from consumer studies, (3) Quantitative tests, (4) Evidence of past substitution patterns, (5) Regulatory requirements. These elements help determine whether consumers would switch to substitute products in response to price increases. The Guide provides practical cases showing how these elements have been applied in real competition cases and their impact on market delimitation.

This extensive section details the Herfindahl-Hirschman Index (HHI) for measuring market concentration through squared market share summation. The HHI ranges from 0 (perfect competition) to 10,000 (pure monopoly). The Department of Justice applies three-tier merger guidelines: post-merger HHI below 1,000 raises no concerns; between 1,000-1,800 requires examining HHI change (over 50-100 points triggers concerns); above 1,800 with significant HHI increases typically gets blocked. Market definition is critical in litigation, with defense arguing broad definitions and prosecution arguing narrow ones. Cross-price elasticity provides statistical evidence of substitutability between products, helping determine competitive relationships. These tools enable regulators to assess whether mergers threaten consumer welfare.

The Herfindahl-Hirschman Index (HHI) measures the level of concentration in a defined market. However, an HHI doesn't mean anything if you're not first determining the correct market definition. There are always disputes about what the relevant market is. HHI matters under merger guidelines and was central to cases like the Philadelphia National Bank case from the 1960s. In the Arch Coal case, the FTC argued against a merger of two coal mines in the Powder River Basin, noting that while the merger might accelerate the transition from coal to natural gas (which might be desirable environmentally), the immediate effect would be higher coal prices hurting consumers. The FTC position was that environmental concerns should be addressed through environmental laws, not antitrust enforcement, demonstrating that competition analysis must focus on consumer welfare rather than broader policy objectives.

Defining the relevant market is the most critical step in any antitrust merger analysis. If defined too broadly, proving anti-competitive effects becomes difficult; if defined too narrowly, almost any merger could be challenged. The DOJ defines the relevant product market as 'the acquisition of U.S. publishing rights to books from authors' and a narrower subset as 'anticipated top-selling books.' Using the Herfindahl-Hirschman Index (HHI), the DOJ argues the merger would create a highly concentrated market (HHI above 2,500) and increase concentration by more than 200 points, triggering the presumption of anti-competitiveness under the Horizontal Merger Guidelines. The hypothetical monopsonist test determines whether a merged buyer could profitably reduce prices paid to suppliers.

Concentration indices measure market structure and potential competitive harm. CR4 (Concentration Ratio for Top 4) calculates the top four firms' share of total sales—for example, firms with 150, 100, 80, and 70 million sales in a 450 million market yield 88.9% concentration. However, CR4 ignores the distribution of remaining firms. HHI (Herfindahl-Hirschman Index) sums squared market shares of all firms, providing a more comprehensive measure. For shares of 40%, 30%, 20%, 9%, and 1%, HHI equals 2982. When firms merge, HHI increases significantly—for instance, merging 20% and 9% shares yields HHI of 3342. According to American merger guidelines, HHI below 1,000 indicates unconcentrated markets, 1,000-1,800 moderately concentrated, and above 1,800 highly concentrated. Mergers significantly increasing HHI in concentrated markets are unlikely approved.

Market share is the percentage of total sales a firm captures. In perfect competition, many firms have tiny market shares. In monopolistic competition, fewer firms have slightly larger shares. In oligopoly, few firms have significant shares. The Herfindahl-Hirschman Index (HHI) measures concentration by summing squared market shares. Higher HHI indicates more concentrated markets. When firms merge, HHI increases. In the US, HHI above 1800 signals dangerous monopolization, and mergers increasing HHI by over 100 points are prohibited.