Duplication of purchase

Duplication of purchase is the law describing how brands' customer bases overlap: every brand shares its buyers with other brands in proportion to the size of those other brands. Buyers of a small beer brand mostly also buy the biggest beer brand, simply because it is the biggest, not because the brands are similar in character. Deviations from the pattern are rare and point to functional submarkets, such as decaf or vegetarian. The law undercuts the idea of neatly separated brand-level target segments: competitors largely fish in the same pond, and niche positions are often smaller than their strategies assume.

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