How Brands Grow

Byron Sharp argues that much of what marketers believe about how brands compete and grow is wrong. Drawing on decades of empirical research conducted by the Ehrenberg-Bass Institute for Marketing Science and its predecessor researchers, Sharp presents scientific laws governing buyer behavior that contradict conventional marketing wisdom. The book challenges widely held assumptions about loyalty, differentiation, targeting, and advertising, proposing instead that brands grow primarily by increasing their mental availability (the propensity to be noticed or thought of in buying situations) and physical availability (the ease with which a brand can be found and purchased) to as many buyers as possible.

Sharp opens with a case study contrasting Crest and Colgate toothpaste in the US market, where Crest holds double Colgate's market share. A fictional brand team interprets Colgate's lower loyalty metrics and higher dependence on "switchers" (buyers who alternate between brands rather than purchasing one exclusively) as signs of brand weakness. Sharp argues these interpretations are wrong: Colgate's metrics are normal for a brand of its size, reflecting market share rather than any underlying problem. He compares modern marketing to pre-scientific medicine, noting that a study by Professor Scott Armstrong of the Wharton School found that nine leading marketing textbooks contained 566 normative statements but almost no supporting empirical evidence.

The first major law Sharp introduces is the double jeopardy law, which states that smaller brands suffer twice: They have far fewer buyers than larger brands, and those buyers are also slightly less loyal. A brand's sales depend on penetration (how many people buy it) and purchase frequency (how often those buyers purchase it). In theory, a small brand could compensate for few buyers through very high loyalty, but this never happens in practice. Data from UK washing powder brands showed that while penetration varied enormously between market leader Persil and smaller brand Surf, average purchase frequency varied only slightly. The same pattern held across UK and US shampoo markets and many other categories. Analysis of market share changes over time consistently showed that brands grew primarily through increased penetration. An analysis of 880 entries to the UK's Institute of Practitioners in Advertising (IPA) Effectiveness Awards found that campaigns aiming to increase penetration were far more likely to win than those targeting loyalty.

Sharp directly challenges the influential 1990 Harvard Business Review claim by Frederick Reichheld and W. Earl Sasser that companies can boost profits by nearly 100% by retaining just 5% more customers. Sharp reveals this claim rested on a thought experiment, not empirical research, and assumed zero cost for halving defection. In reality, defection rates also follow double jeopardy. Doctoral research by Erica Riebe, examining pharmaceutical brands over 10 years and replicated in French consumer goods and banking data, found that growing brands achieved growth almost entirely through higher-than-expected customer acquisition rather than lower defection. Declining brands showed normal defection but poor acquisition.

Sharp challenges the Pareto principle by presenting evidence that the top 20% of buyers typically account for only about 60% of sales over a year, not the commonly cited 80%. Purchase frequency follows a highly skewed distribution described by the negative binomial distribution (NBD), a statistical model capturing how most buyers purchase infrequently while a small fraction buys very often. The law of buyer moderation, a regression-to-the-mean phenomenon, further undermines strategies targeting heavy buyers: Heavy buyers in one period buy less in the next, light buyers buy more, and some non-buyers become buyers. A two-year analysis of a US tomato sauce brand showed that 14% of second-year sales came from households classified as non-buyers in the first year, while heavy buyers' share of volume dropped from 43% to 34%. Sharp argues that marketing must reach all buyers, including the vast majority who are light and occasional.

The book challenges targeting assumptions by showing that competing brands sell to nearly identical customer bases. A landmark 1959 study by Professor Franklin B. Evans found that the personality profiles of Ford and Chevrolet owners were essentially identical, a finding confirmed repeatedly in subsequent decades. Ehrenberg-Bass Institute studies profiling hundreds of brands using demographics, psychographics (lifestyle- and personality-based consumer traits), attitudes, values, and media habits found that the typical deviation from the brand norm averaged only about two percentage points. Even Nestlé's Yorkie chocolate bar, marketed with the slogan "It's not for girls!" still drew 44% of its buyers from women. Sharp describes the "I love my Mum" phenomenon: Buyers of different brands express very similar attitudes about their respective brands because behavior drives attitude, not the reverse.

Using the duplication of purchase law, Sharp demonstrates that brands compete broadly across entire categories rather than within narrow segments. All brands share customers with other brands in proportion to those brands' market shares. The author contrasts this finding with perceptual maps (charts showing how consumers perceive brands relative to each other), which often imply dramatic segmentation that actual buying data does not support. Sharp concludes that most markets function as mass markets with only slight fragmentation.

Sharp dismantles the mythology of passionate brand loyalty, arguing it is prosaic and polygamous. Across multiple UK categories, on average only 13% of a brand's buyers are 100% loyal over a year. Apple's repeat-purchase rate of 55% is only slightly above competitors such as HP/Compaq and Gateway (both 52%), and Sharp attributes Apple's modest advantage largely to switching costs rather than passionate commitment. A segmentation study of Harley-Davidson riders found that the most passionately loyal segments contributed less than 10% of sales revenue.

Sharp argues that meaningful perceived differentiation plays a far smaller role than textbooks claim. Research across 16 categories showed that on average only about 10% of a brand's users considered their brand "different" or "unique." The NBD-Dirichlet model, which predicts brand metrics by assuming brands compete as undifferentiated options of varying popularity, successfully fit real-world data across dozens of categories. Sharp proposes distinctiveness as the alternative: Brands should build distinctive assets, such as colors, logos, taglines, and advertising styles, that make the brand easy to notice and recall.

On advertising, Sharp presents a model centered on memory rather than persuasion. Advertising works primarily by refreshing memory structures that increase the probability a brand will be recalled in buying situations, reaching millions of light buyers and nudging their purchase probability slightly upward. This contrasts with price promotions, whose effects are concentrated in a single week. Co-authors John Dawes and John Scriven examine price promotions in detail, finding they generate short-term sales spikes but no lasting effects; almost everyone who buys a brand during a promotion has bought it before. Break-even analysis shows these volume increases often fail to generate incremental profit because the contribution margin per unit drops disproportionately. Sharp also presents evidence that loyalty programs produce negligible effects, as they inherently skew toward existing loyal buyers rather than attracting new ones.

In the synthesizing chapter, Sharp argues that consumers are busy, satisficing (settling for adequate rather than optimal choices) decision-makers who screen out most brands before evaluation; getting into consumers' consideration sets (the small group of brands a buyer seriously considers) matters far more than winning feature comparisons. He uses McDonald's early-2000s turnaround as an example: Rather than innovating, the company undertook catch-up efforts that removed reasons not to buy and leveraged its existing mental and physical availability. Sharp distills the book into seven rules: continuously reach all category buyers, ensure the brand is easy to buy, get noticed, refresh and build memory structures, create distinctive brand assets, maintain consistency while staying fresh, and avoid giving consumers reasons to reject the brand. Marketing departments, Sharp argues, should reconceive themselves as custodians of mental and physical availability, and the real advances in marketing effectiveness will come from the application of well-established scientific laws.