Francis Galton’s cattle-weight estimation experiment took place at a livestock fair in Plymouth in 1906. By averaging 787 estimates of an ox’s dressed weight, Galton found that a varied crowd had guessed within one pound of the truth—an outcome that unsettled his assumption that sound judgment belonged chiefly to a select, highly capable few. The episode introduces the book’s argument that diverse judgments, when gathered together, can produce a remarkably accurate collective answer.

Setting and Purpose

In the fall of 1906, eighty-five-year-old Galton left his home in Plymouth for the annual West of England Fat Stock and Poultry Exhibition. A gathering place for farmers and townspeople to appraise livestock, the fair also suited Galton’s longstanding interests in measurement and breeding. He had spent much of his career trying to identify and measure the qualities he believed were necessary for social leadership, and his earlier experiments had left him skeptical of the intelligence of the general population.

The competition he encountered offered an unplanned test of that skepticism. A fat ox had been put on display, and visitors could pay sixpence for a numbered ticket on which they wrote their name, address, and estimate of the animal’s weight after slaughter and dressing. The best guesses would win prizes. Galton saw in this contest an analogy to democratic judgment: participants had unequal abilities and experience, just as voters did when assessing political questions.

The Crowd’s Estimate

Eight hundred people entered. Some were butchers and farmers, with relevant experience judging livestock; others had no special knowledge of cattle. Once the contest ended and prizes had been awarded, Galton borrowed the tickets from the organizers and analyzed the estimates. Thirteen were illegible, leaving 787 usable guesses. He arranged them from highest to lowest, graphed their distribution to see whether it formed a bell curve, and calculated their mean—the answer the crowd would have given if it were a single person.

The result was strikingly close. The group’s average estimate was 1,197 pounds; the dressed ox weighed 1,198 pounds. Galton had expected that combining a few capable judges with many less capable ones would yield a poor answer. Instead, the average missed by only one pound. He later described the outcome as more favorable to the trustworthiness of democratic judgment than he would have expected, a concession that cut against his prior distrust of the average voter.

Meaning and Limits

The experiment’s force lies in the contrast between the crowd’s varied and uneven expertise and the precision of its combined estimate. It did not show that every participant was well informed or that any individual guess was reliable. Rather, the mean brought the separate judgments together into an answer that was almost exactly right. In the book’s account, this is an early example of a broader principle: groups can be collectively intelligent without being led by their most intelligent members.

The book connects that principle to four conditions for wise crowds: diversity of opinion, independent judgment, decentralization, and a way to aggregate individual views. When a sufficiently diverse and independent group makes estimates, individual errors can offset one another, allowing the information held across the group to become visible in its combined judgment. Galton’s fairground calculation illustrates the potential of that mechanism, but the book’s argument is conditional: aggregation can yield a wise answer only when the individual judgments contain information and the group’s organization allows it to be brought together.

Role in the Book

The experiment opens the book with a modest, measurable question—the weight of an ox—and a result that reverses Galton’s expectations. It establishes the central puzzle before the discussion turns to more complex cases, including a lost submarine and the market’s response to the Challenger disaster. Those examples differ greatly in scale, but the book presents them as related demonstrations of how separate judgments can combine into a useful picture that no one participant may possess alone.