The Wisdom of Crowds: Why the Many Are Smarter Than the Few and How Collective Wisdom Shapes Business, Economies, Societies and Nations by James Surowiecki, James Surowiecki

From the Publisher

“No one in this world, so far as I know, has ever lost money by underestimating the intelligence of the great masses of the plain people.”  —H. L. Mencken
 
H. L. Mencken was wrong.

In this endlessly fascinating book, New Yorker columnist James Surowiecki explores a deceptively simple idea that has profound implications: large groups of people are smarter than an elite few, no matter how brilliant—better at solving problems, fostering innovation, coming to wise decisions, even predicting the future.

This seemingly counterintuitive notion has endless and major ramifications for how businesses operate, how knowledge is advanced, how economies are (or should be) organized and how we live our daily lives. With seemingly boundless erudition and in delightfully clear prose, Surowiecki ranges across fields as diverse as popular culture, psychology, ant biology, economic behaviorism, artificial intelligence, military history and political theory to show just how this principle operates in the real world. 

Despite the sophistication of his arguments, Surowiecki presents them in a wonderfully entertaining manner. The examples he uses are all down-to-earth, surprising, and fun to ponder. Why is the line in which you’re standing always the longest? Why is it that you can buy a screw anywhere in the world and it will fit a bolt bought ten-thousand miles away? Why is network television so awful? If you had to meet someone in Paris on a specific day but had no way of contacting them, when and where would you meet? Why are there traffic jams? What’s the best way to win money on a game show?Why, when you walk into a convenience store at 2:00 A.M. to buy a quart of orange juice, is it there waiting for you? What do Hollywood mafia movies have to teach us about why corporations exist?

The Wisdom of Crowds is a brilliant but accessible biography of an idea, one with important lessons for how we live our lives, select our leaders, conduct our business, and think about our world.

The Washington Post - Eric Klinenberg

… Surowiecki, who has fashioned a fascinating financial column in the New Yorker by using cutting-edge social science research to interpret market life, finds ample evidence to support his argument. He writes with command and flair, weaving together entertaining anecdotes from popular culture and business history and accessible summaries of arcane theoretical debates in behavioral economics, sociology and psychology. The Wisdom of Crowds is both intellectually challenging and a pleasure to read.

Publishers Weekly

While our culture generally trusts experts and distrusts the wisdom of the masses, New Yorker business columnist Surowiecki argues that "under the right circumstances, groups are remarkably intelligent, and are often smarter than the smartest people in them." To support this almost counterintuitive proposition, Surowiecki explores problems involving cognition (we're all trying to identify a correct answer), coordination (we need to synchronize our individual activities with others) and cooperation (we have to act together despite our self-interest). His rubric, then, covers a range of problems, including driving in traffic, competing on TV game shows, maximizing stock market performance, voting for political candidates, navigating busy sidewalks, tracking SARS and designing Internet search engines like Google. If four basic conditions are met, a crowd's "collective intelligence" will produce better outcomes than a small group of experts, Surowiecki says, even if members of the crowd don't know all the facts or choose, individually, to act irrationally. "Wise crowds" need (1) diversity of opinion; (2) independence of members from one another; (3) decentralization; and (4) a good method for aggregating opinions. The diversity brings in different information; independence keeps people from being swayed by a single opinion leader; people's errors balance each other out; and including all opinions guarantees that the results are "smarter" than if a single expert had been in charge. Surowiecki's style is pleasantly informal, a tactical disguise for what might otherwise be rather dense material. He offers a great introduction to applied behavioral economics and game theory. Agent, Chris Calhoun. (On sale May 18) Forecast: While armchair social scientists (e.g., readers of The Tipping Point) will find this book interesting, college economics, math, statistics and finance students could really profit from spending time with Surowiecki. National author promos and print ads will attract buyers. Copyright 2004 Reed Business Information.

Library Journal

According to Surowiecki, the "simple but powerful truth" at the heart of his book is that "under the right circumstances, groups are remarkably intelligent, and are often smarter than the smartest people in them." Surowiecki, a staff writer for the Financial Page of The New Yorker, analyzes the concept of collective wisdom and applies it to various areas of the social sciences, including economics and politics. The author examines three kinds of problems involved in collective wisdom: cognition, or problems with definite solutions; coordination, where members of a group figure out how to coordinate their behavior with one another; and cooperation, involving getting self-centered individuals to work together. Part 1 studies the three problems (cognition, coordination, and cooperation) and the factors it takes for the crowd to be wise (diversity, dependence, and a specific type of decentralization). Part 2 contains case studies illustrating both success and failure of collective intelligence. Surowiecki also draws upon studies and works of past theorists of collective intelligence, including Charles Mackay's landmark Extraordinary Popular Delusions and the Madness of Crowds. This work is an intriguing study of collective intelligence and how it works in contemporary society. Recommended for larger public and academic library collections.-Lucy Heckman, St. John's Univ. Lib., Jamaica, NY Copyright 2004 Reed Business Information.

Soundview Summary - Soundview Executive Book Summaries

Western society is focused on the power of the individual mind, but under the right circumstances, groups can actually make better decisions than even the smartest person within them. When individuals in a crowd are appropriately diverse, independent and decentralized, their aggregated decisions are surprisingly on point. With this knowledge, the power of groups can be used to find unknown answers and determine how to coordinate behavior and cooperate in all areas of society. Our everyday activities, our government and our economy are all affected by the power of crowds, and when things go awry, it is often because one of the key elements of an intelligent crowd is missing or underexpressed.

In The Wisdom of Crowds, journalist James Surowiecki explores the underlying implications of the idea that large groups of people are smarter than an elite few, no matter how brilliant.

Tapping Into Crowds
In 1906, British scientist Francis Galton watched a weight-judging competition at a livestock fair. People bet on the weight of an ox after it was slaughtered and dressed. Butchers, farmers and nonexperts all bought tickets and guessed.

Galton borrowed the tickets after the competition and calculated the mean of the 787 guesses — the collective wisdom of the group. The crowd guessed 1,197 pounds. After the ox was slaughtered and dressed, it weighed 1,198 pounds. Galton had discovered that, under the right circumstances, groups are remarkably intelligent and often smarter than the smartest people in them, especially if individual guesses are aggregated and averaged. The group is not better than every single person, and some individuals will be smarter the more incentive they receive, such as in the stock market. But it is rare that the same person will be right as consistently as the group.

Game Show Contestants
On the TV show Who Wants to be a Millionaire, contestants answered a series of four-answer, multiple-choice questions. When stumped, they could have two choices of answers removed, call a smart friend or poll the audience. The smart people were right 65 percent of the time, but the studio audience was right 91 percent of the time.

Cognition problems can also have answers that are unknown or in the future. For example:
Within 21 minutes of the 1986 Challenger explosion, the stock price of Morton Thiokol had fallen well below that of the other three companies involved in building the shuttle. Six months later, the cause of the explosion was determined to be the O-ring seals on the booster rockets made by Thiokol.

The Iowa Electronic Markets (IEM), made up of about 800 people buying and selling futures on different election outcomes, is often more accurate than national polls.

Futures markets like the IEM exist for Hollywood box office receipts, news and sports. They work because they have the fundamental characteristics — diversity, independence and decentralization — that are key to making good predictions.

The Difference Difference Makes

Ransom E. Olds started selling cars in 1899 and prospered by selling the curved-dash Olds: a car for the middle class. With amazing marketing, he did quite well and sold more cars than any other U.S. manufacturer in 1903. Olds had fierce competition from hundreds of automobile companies. There was no standard, so they were peddling a huge array of vehicles with different sizes, shapes and power generators. Toward the end of the decade, most contenders began to fade, but innovators like Cadillac and Ford stayed. By World War I, Olds had been bought by General Motors.

The histories of most new industries are similar — a profusion of alternatives in the early days and a winnowing out of the winners who effectively choose the prevailing technologies. It seems inefficient, but the diversity of ideas allows meaningful differences among early ideas, not just minor variations on the same concept. The system works when it can recognize losers and kill them off quickly.

It is not enough to generate a diverse set of possible solutions. The crowd also needs to be able to distinguish the good from the bad. Diversity adds perspectives that would otherwise be absent and makes a group better at solving problems. In fact, grouping only smart people together might not be that good an idea because they tend to resemble each other in skills. Adding people who know less but have different skills improves the group's performance. A group with diverse knowledge and skills will almost always make a better decision than one or two experts. Copyright © 2005 Soundview Executive Book Summaries

Kirkus Reviews

Multitudes are generally smarter than their smartest members, declares New Yorker writer Surowiecki. With his theory of the inherent sagacity of large groups, Surowiecki seems to differ with Scottish journalist Charles Mackay's 1841 classic, Memoirs of Extraordinary Popular Delusions and the Madness of Crowds, which dealt with such stupidities as the South Sea Bubble, tulip-mania, odd styles of whiskers, and dueling. Our 21st-century author admits that there are impediments and constraints to the intelligence of large groups, usually problems of cognition, coordination, and cooperation. A group must have knowledge, Surowiecki states: not extensive knowledge, but rudimentary comprehension of basic fact with harmonized behavior by individual members. Finally, individuals must go beyond self-interest for the good of all. That's how capital markets and Google's algorithm work, and how science isolated the SARS virus. Lack of the basics leads to traffic jams, the dot-com crash, and the Columbia shuttle mission disaster. If crowds are inherently clever, a reader may be prompted to ask, just how smart is a flock of turkeys? Not very smart, certainly, but smarter, Surowiecki would assert, than the smartest turkey individual. A school of herring is going to be more intelligent than any single fish in it. All this may be less than encouraging to hot-stock analysts, high-profile CEOs, and others who sell their personal expertise for a high salary, but the author argues persuasively that collective wisdom works better than the intelligent fiat of any individual. His wide-ranging study links psychology and game theory, economics and management theory, social science and public policy. And it advancesMackay's report from times when, as the Scot put it, "knavery gathered a rich harvest from cupidity."Valuable insights regarding information cascades, crowd herding, cognitive collaboration, and group polarization. There is some individual, independent wisdom to be found here.

What People Are Saying

Malcolm Gladwell
The Wisdom of Crowds is dazzling. It is one of those books that will turn your world upside down. It's an adventure story, a manifesto, and the most brilliant book on business, society, and everyday life that I've read in years.
—author of The Tipping Point

Po Bronson
This book should be in every thinking businessperson's library. Without exception. At a time when corporate leaders have shown they're not always deserving of our trust, James Surowiecki has brilliantly revealed that we can trust each other. That we count. That our collective effort is far more important than the lofty predictions of those CEO-kings we have worshipped for too long.
—author of What Should I Do With My Life?

Kenneth Arrow
It has become increasingly recognized that the average opinions of groups is frequently more accurate than most individuals in the group. As a special case, economists have spoken of the role of markets in assembling dispersed information. The author has written a most interesting survey of the many studies in this area and discussed the limits as well as the achievements of self-organization.
—winner of the Nobel Prize in Economics and Professor of Economics (Emeritus), Stanford University

Product Details

• ISBN: 0385721706
  
• ISBN-13: 9780385721707
• Format: Paperback, 320pp
• Publisher: Random House Inc
• Pub. Date: August 2005
• Edition Description: Reprint
• Sales Rank: 7,099

• Interviews & Essays
• Read an Excerpt

Interviews & Essays

This was no party trick. Instead, the jellybean-counting experiment demonstrated something I call the wisdom of crowds: under the right circumstances, groups are remarkably intelligent, and are often smarter than the smartest people in them. A group does not need to be dominated by exceptionally intelligent people in order to be smart. Even if most of the people within a group are not especially well-informed or rational, collectively they can still be brilliant.

The wisdom of crowds is at work all around us, although it's easy to miss. It helps explain why the economy works well at getting people what they want as cheaply as possible, even though no one is in charge of the economy as a whole. It helps explain why people in a healthy society cooperate with each other by doing things like paying taxes and contributing to charities. And it explains why, if you're trying to solve a problem with a definitive answer, you're better off with the group than with even the most well-informed expert.

Take the show Who Wants to Be a Millionaire. When a contestant on the show is stumped by a question, he can ask the audience for help or consult someone he's designated as an expert. The experts do a reasonable job: they get the answer right 65 percent of the time. But the audience is close to perfect: it gets the answer right 91 percent of the time. Similarly, at the race track, the final odds on a race reliably predict the race's order of finish (that is, the favorite wins most often, the horse with the second-lowest odds wins second most often, and so on) and also uncannily predict how likely it is that a horse will win. In other words, horses that run at 3-to-1 odds win just about a quarter of the time. The Hollywood Stock Exchange -- a kind of online stock market where people can wager on how movies will do at the box office -- has become a more reliable forecaster of ticket sales than any other method. And in the stock market, for all of its crazy swings, it's very difficult for even the best money managers to do better than the market as a whole.

So what's the catch? Simply this: not all crowds are wise. Groups can only be smart if they're made up of people with diverse information who are making decisions relatively independently. Groups that are too much alike get stuck because they don't have access to enough information and because they favor harmony over dissent. The wisdom of crowds isn't about consensus or compromise, so groups in which everyone agrees are likely to be less intelligent. Similarly, when people are worried too much about what others think, groups get dumber, too. The real paradox of the wisdom of crowds is that the way for the group to be smart is for each person to act as an individual. When they don't -- like during a stock-market bubble, where people buy stocks only because they think they can dump them on someone else -- groups go wrong.

Wise crowds, then, are diverse, independent, and decentralized. As it happens, that means that one place that is tailor-made for the wisdom of crowds is the Internet. Because no one is in charge of the Net, and because it features a cacophony of diverse voices, with no one voice being loud enough to drown out others, the Internet's collective intelligence is potentially immense. One place you can see this is in the plethora of rating systems for everything from consumer electronics to -- as on this site -- books. Until recently, there was no way to aggregate the judgments of readers or TV watchers across the country, let alone the world. So most of the information a person got came from a relatively small circle of friends and acquaintances. Today, we can draw on a far more diverse and eclectic pool of information. To the degree that we do so, our decisions will be better as a result.

The most striking example of the wisdom of crowds on the Net is, of course, Google. Google is able to routinely survey 4.3 billion web pages and pick exactly the one that has the information that you are looking for. And it does this by relying on the collective intelligence of the Web. Roughly speaking, Google finds the right pages by asking Web page producers to vote on which other pages are most worthwhile, with each link to a page counting as a vote. Google is a republic, not a pure democracy; the more people that have linked to a given page, the more influence that page has on the group's final decision. But the principle is fundamentally democratic -- let the masses decide. Far more often than not, they decide wisely.

Most of us, whether as voters or investors or consumers or managers, believe that valuable knowledge is concentrated in a very few hands (or, rather, in a very few heads). We assume that the key to solving problems or making good decisions is finding that one right person who will have the answer. But Jack Treynor's jellybean experiment and Google's success should teach us a different lesson. When it comes to problem-solving, stop looking for that one right person. Ask the crowd instead. Chances are, it knows. James Surowiecki

Read an Excerpt

The Wisdom of Crowds


I


If, years hence, people remember anything about the TV game show Who Wants to Be a Millionaire?, they will probably remember the contestants' panicked phone calls to friends and relatives. Or they may have a faint memory of that short-lived moment when Regis Philbin became a fashion icon for his willingness to wear a dark blue tie with a dark blue shirt. What people probably won't remember is that every week Who Wants to Be a Millionaire? pitted group intelligence against individual intelligence, and that every week, group intelligence won.

Who Wants to Be a Millionaire? was a simple show in terms of structure: a contestant was asked multiple-choice questions, which got successively more difficult, and if she answered fifteen questions in a row correctly, she walked away with $1 million. The show's gimmick was that if a contestant got stumped by a question, she could pursue three avenues of assistance. First, she could have two of the four multiple-choice answers removed (so she'd have at least a fifty-fifty shot at the right response). Second, she could place a call to a friend or relative, a person whom, before the show, she had singled out as one of the smartest people she knew, and ask him or her for the answer. And third, she could poll the studio audience, which would immediately cast its votes by computer. Everything we think we know about intelligence suggests that the smart individual would offer the most help. And, in fact, the "experts" did okay, offering the right answer—under pressure—almost 65 percent of the time. But they paled in comparison to the audiences. Those randomcrowds of people with nothing better to do on a weekday afternoon than sit in a TV studio picked the right answer 91 percent of the time.

Now, the results of Who Wants to Be a Millionaire? would never stand up to scientific scrutiny. We don't know how smart the experts were, so we don't know how impressive outperforming them was. And since the experts and the audiences didn't always answer the same questions, it's possible, though not likely, that the audiences were asked easier questions. Even so, it's hard to resist the thought that the success of the Millionaire audience was a modern example of the same phenomenon that Francis Galton caught a glimpse of a century ago.

As it happens, the possibilities of group intelligence, at least when it came to judging questions of fact, were demonstrated by a host of experiments conducted by American sociologists and psychologists between 1920 and the mid-1950s, the heyday of research into group dynamics. Although in general, as we'll see, the bigger the crowd the better, the groups in most of these early

experiments—which for some reason remained relatively unknown outside of academia—were relatively small. Yet they nonetheless performed very well. The Columbia sociologist Hazel Knight kicked things off with a series of studies in the early 1920s, the first of which had the virtue of simplicity. In that study Knight asked the students in her class to estimate the room's temperature, and then took a simple average of the estimates. The group guessed 72.4 degrees, while the actual temperature was 72 degrees. This was not, to be sure, the most auspicious beginning, since classroom temperatures are so stable that it's hard to imagine a class's estimate being too far off base. But in the years that followed, far more convincing evidence emerged, as students and soldiers across America were subjected to a barrage of puzzles, intelligence tests, and word games. The sociologist Kate H. Gordon asked two hundred students to rank items by weight, and found that the group's "estimate" was 94 percent accurate, which was better than all but five of the individual guesses. In another experiment students were asked to look at ten piles of buckshot—each a slightly different size than the rest—that had been glued to a piece of white cardboard, and rank them by size. This time, the group's guess was 94.5 percent accurate. A classic demonstration of group intelligence is the jelly-beans-in-the-jar experiment, in which invariably the group's estimate is superior to the vast majority of the individual guesses. When finance professor Jack Treynor ran the experiment in his class with a jar that held 850 beans, the group estimate was 871. Only one of the fifty-six people in the class made a better guess.

There are two lessons to draw from these experiments. First, in most of them the members of the group were not talking to each other or working on a problem together. They were making individual guesses, which were aggregated and then averaged. This is exactly what Galton did, and it is likely to produce excellent results. (In a later chapter, we'll see how having members interact changes things, sometimes for the better, sometimes for the worse.) Second, the group's guess will not be better than that of every single person in the group each time. In many (perhaps most) cases, there will be a few people who do better than the group. This is, in some sense, a good thing, since especially in situations where there is an incentive for doing well (like, say, the stock market) it gives people reason to keep participating. But there is no evidence in these studies that certain people consistently outperform the group. In other words, if you run ten different jelly-bean-counting experiments, it's likely that each time one or two students will outperform the group. But they will not be the same students each time. Over the ten experiments, the group's performance will almost certainly be the best possible. The simplest way to get reliably good answers is just to ask the group each time.

A similarly blunt approach also seems to work when wrestling with other kinds of problems. The theoretical physicist Norman L. Johnson has demonstrated this using computer simulations of individual "agents" making their way through a maze. Johnson, who does his work at the Los Alamos National Laboratory, was interested in understanding how groups might be able to solve problems that individuals on their own found difficult. So he built a maze—one that could be navigated via many different paths, some shorter, and some longer—and sent a group of agents into the maze one by one. The first time through, they just wandered around, the way you would if you were looking for a particular cafe* in a city where you'd never been before. Whenever they came to a turning point—what Johnson called a "node"—they would randomly choose to go right or left. Therefore some people found their way, by chance, to the exit quickly, others more slowly. Then Johnson sent the agents back into the maze, but this time he allowed them to use the information they'd learned on their first trip, as if they'd dropped bread crumbs behind them the first time around. Johnson wanted to know how well his agents would use their new information. Predictably enough, they used it well, and were much smarter the second time through. The average agent took 34.3 steps to find the exit the first time, and just 12.8 steps to find it the second.

The key to the experiment, though, was this: Johnson took the results of all the trips through the maze and used them to calculate what he called the group's "collective solution." He figured out what a majority of the group did at each node of the maze, and then plotted a path through the maze based on the majority's decisions. (If more people turned left than right at a given node, that was the direction he assumed the group took. Tie votes were broken randomly.) The group's path was just nine steps long, which was not only shorter than the path of the average individual (12.8 steps), but as short as the path that even the smartest individual had been able to come up with. It was also as good an answer as you could find. There was no way to get through the maze in fewer than nine steps, so the group had discovered the optimal solution. The obvious question that follows, though, is: The judgment of crowds may be good in laboratory settings and classrooms, but what happens in the real world?


II


At 11:38 am on January 28, 1986, the space shuttle Challenger lifted off from its launch pad at Cape Canaveral. Seventy-four seconds later, it was ten miles high and rising. Then it blew up. The launch was televised, so news of the accident spread quickly. Eight minutes after the explosion, the first story hit the Dow Jones News Wire.

The stock market did not pause to mourn. Within minutes, investors started dumping the stocks of the four major contractors who had participated in the Challenger launch: Rockwell International, which built the shuttle and its main engines; Lockheed, which managed ground support; Martin Marietta, which manufactured the ship's external fuel tank; and Morton Thiokol, which built the solid-fuel booster rocket. Twenty-one minutes after the explosion, Lockheed's stock was down 5 percent, Martin Marietta's was down 3 percent, and Rockwell was down 6 percent.

Morton Thiokol's stock was hit hardest of all. As the finance professors Michael T. Maloney and J. Harold Mulherin report in their fascinating study of the market's reaction to the Challenger disaster, so many investors were trying to sell Thiokol stock and so few people were interested in buying it that a trading halt was called almost immediately. When the stock started trading again, almost an hour after the explosion, it was down 6 percent. By the end of the day, its decline had almost doubled, so that at market close, Thiokol's stock was down nearly 12 percent. By contrast, the stocks of the three other firms started to creep back up, and by the end of the day their value had fallen only around 3 percent.

What this means is that the stock market had, almost immediately, labeled Morton Thiokol as the company that was responsible for the Challenger disaster. The stock market is, at least in theory, a machine for calculating the present value of all the "free cash flow" a company will earn in the future. (Free cash flow is the money that's left over after a company has paid all its bills and its taxes, has accounted for depreciation, and has invested in the business. It's the money you'd get to take home and put in the bank if you were the sole owner of the company.) The steep decline in Thiokol's stock price—especially compared with the slight declines in the stock prices of its competitors—was an unmistakable sign that investors believed that Thiokol was responsible, and that the consequences for its bottom line would be severe.

As Maloney and Mulherin point out, though, on the day of the disaster there were no public comments singling out Thiokol as the guilty party. While the New York Times article on the disaster that appeared the next morning did mention two rumors that had been making the rounds, neither of the rumors implicated Thiokol, and the Times declared, "There are no clues to the cause of the accident."

Regardless, the market was right. Six months after the explosion, the Presidential Commission on the Challenger revealed that the O-ring seals on the booster rockets made by Thiokol—seals that were supposed to prevent hot exhaust gases from escaping—became less resilient in cold weather, creating gaps that allowed the gases to leak out. (The physicist Richard Feynman famously demonstrated this at a congressional hearing by dropping an O-ring in a glass of ice water. When he pulled it out, the drop in temperature had made it brittle.) In the case of the Challenger, the hot gases had escaped and burned into the main fuel tank, causing the cataclysmic explosion. Thiokol was held liable for the accident. The other companies were exonerated.

In other words, within a half hour of the shuttle blowing up, the stock market knew what company was responsible. To be sure, this was a single event, and it's possible that the market's singling out of Thiokol was just luck. Or perhaps the company's business seemed especially susceptible to a downturn in the space program. Possibly the trading halt had sent a signal to investors to be wary. These all are important cautions, but there is still something eerie about what the market did. That's especially true because in this case the stock market was working as a pure weighing machine, undistorted by the factors—media speculation, momentum trading, and Wall Street hype—that make it a peculiarly erratic mechanism for aggregating the collective wisdom of investors. That day, it was just buyers and sellers trying to figure out what happened and getting it right.

How did they get it right? That's the question that Maloney and Mulherin found so vexing. First, they looked at the records of insider trades to see if Thiokol executives, who might have known that their company was responsible, had dumped stock on January 28. They hadn't. Nor had executives at Thiokol's competitors, who might have heard about the O-rings and sold Thiokol's stock short. There was no evidence that anyone had dumped Thiokol stock while buying the stocks of the other three contractors (which would have been the logical trade for someone with inside information). Savvy insiders alone did not cause that first-day drop in Thiokol's price. It was all those investors—most of them relatively uninformed—who simply refused to buy the stock.

But why did they not want Thiokol's stock? Maloney and Mulherin were finally unable to come up with a convincing answer to that question. In the end, they assumed that insider information was responsible for the fall in Thiokol's price, but they could not explain how. Tellingly, they quoted the Cornell economist Maureen O'Hara, who has said, "While markets appear to work in practice, we are not sure how they work in theory."

Maybe. But it depends on what you mean by "theory." If you strip the story down to its basics, after all, what happened that January day was this: a large group of individuals (the actual and potential shareholders of Thiokol's stock, and the stocks of its competitors) was asked a question—"How much less are these four companies worth now that the Challenger has exploded?"—that had an objectively correct answer. Those are conditions under which a crowd's average estimate—which is, dollar weighted, what a stock price is—is likely to be accurate. Perhaps someone did, in fact, have inside knowledge of what had happened to the O-rings. But even if no one did, it's plausible that once you aggregated all the bits of information about the explosion that all the traders in the market had in their heads that day, it added up to something close to the truth. As was true of those who helped John Craven find the Scorpion, even if none of the traders was sure that Thiokol was responsible, collectively they were certain it was.