Why the HHI Is the Regulatory Metric Your Industry Analysis Can't Ignore

Is Your Industry Analysis Missing the Metric That Actually Matters?

Every industry analyst worth their salt can rattle off a market's CAGR and size. But when was the last time you checked its Herfindahl-Hirschman Index? If the answer is "never," you're flying blind. The HHI is the single most important regulatory metric you can add to your toolkit, and ignoring it is a luxury you can't afford.

Here's the contrarian take: growth rates are seductive but often misleading. A fast-growing market can still be a regulatory minefield if it's concentrated. The HHI tells you how concentrated your market is, and that's the number regulators actually use to decide whether to block a merger. If you're not tracking it, you're not doing your job.

What the HHI Actually Tells You

The Herfindahl-Hirschman Index is simple to calculate: sum the squares of each firm's market share. A market with many small players approaches zero; a monopoly hits 10,000. The US Department of Justice uses this number to classify markets. Under the 2023 Merger Guidelines, a market is "moderately concentrated" when the HHI is between 1,000 and 1,800, and "highly concentrated" when it exceeds 1,800 (US DOJ Antitrust Division).

That threshold isn't academic. If your industry's HHI creeps above 1,800, you're in the red zone. Any merger that pushes the HHI up by more than 100 points is presumed unlawful (US DOJ Antitrust Division). Even if you're not planning a merger, this affects you. A competitor's acquisition could get blocked, changing the competitive landscape you've been analyzing.

Why Growth Isn't a Shield

Let's be blunt: a high growth rate doesn't protect you from antitrust scrutiny. Consider the global market research industry. It was valued at about $76.37 billion in 2021 and projected to reach over $108 billion by 2026 (Similarweb / Research and Markets). That's a healthy CAGR. But if the top five firms hold 80% of the market, the HHI is sky-high, and regulators will treat it differently than a fragmented market with the same growth.

Take the US, which holds about 53% of the global market research market (Similarweb / Research and Markets). That's a dominant share, and any consolidation among the top players would likely trigger an HHI red flag. Growth doesn't erase concentration risk; it amplifies it. The faster the market grows, the more attractive it becomes for M&A, and the more likely regulators are to intervene.

How to Use the HHI in Your Next Analysis

Here's a straightforward approach:

• Step 1: Estimate market shares for the top players in your defined market. If you can't get exact figures, use your best judgment based on revenue data.
• Step 2: Square each share (as a percentage) and sum the squares. That's your HHI.
• Step 3: Compare it to the DOJ's thresholds. If you're above 1,800, flag it as high regulatory risk.

For example, imagine a market with five firms: 30%, 25%, 20%, 15%, and 10%. Squaring those gives 900 + 625 + 400 + 225 + 100 = 2,250. That's highly concentrated. A merger between the 15% and 10% firms would increase the HHI by 300 points, blowing past the 100-point presumption threshold (US DOJ Antitrust Division).

Now, apply that to the pharma sector, which accounts for about 16.6% of market research spending (Similarweb / Research and Markets). If the top pharma companies are consolidating, the HHI for that segment could rise, and regulators might scrutinize data access or pricing. It's not just about the overall market; you need to analyze the HHI for the strategically relevant market (SRM) you care about.

The Bottom Line: Add the HHI to Your Standard Toolkit

The CFA Institute recommends using Porter's Five Forces to interpret the competitive environment and PESTLE to understand external trends. But neither framework explicitly addresses concentration risk. That's a gap you can fill. When you're doing your next industry analysis, don't stop at CAGR and market size. Calculate the HHI, check it against the DOJ thresholds, and you'll have a concrete, data-driven measure of regulatory risk that most analysts ignore.

Sources

• US DOJ Antitrust Division - https://www.justice.gov/atr/herfindahl-hirschman-index
• Similarweb / Research and Markets - https://www.similarweb.com/blog/research/market-research/market-research-stats/
• CFA Institute - https://www.cfainstitute.org/insights/professional-learning/refresher-readings/2026/industry-and-competitive-analysis