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Glossary
HHI
HHI, or Herfindahl-Hirschman Index, measures market concentration by summing squared market shares.
Why it matters
It helps teams read market structure and quickly identify areas where a transaction may materially increase concentration.
In practice
HHI becomes most useful when it is read with pre-deal HHI, post-deal HHI and delta HHI inside a well-defined local market.
Common mistake
Treating HHI as a standalone number without considering local market structure, store formats and perimeter logic.
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