This morning’s news brought me results from the following polls: 37% of Americans say they will not vote for a Mormon for president; 89% think that Cubans will be better off with Castro gone; 25% will not visit the dentist for fear of pain, and, in response, 5% of dentists now offer massages, facials, manicures, and warm towels. Is this information valuable? As for the Cubans, surely not. What could it possibly mean that Americans think Cubans will be better off without Castro? As for the dentists, perhaps there is some value. My dentist, at least, now knows how to get more of my business. And as for Governor Romney of Massachusetts, those numbers certainly sound impressive. Shouldn’t he just quit now? Perhaps, if a different poll wasn’t telling him otherwise. “If you did a poll,” said Romney, “and asked ‘Could a divorced actor be president?,’ my guess is 70% would say no. But then they saw Ronald Reagan.” It is easy to miss just how nifty this response is. Confronted with an actual poll, Mr. Romney parries with a hypothetical poll of his own, complete with hypothetical results.

How the country got itself into this mess is the subject of Sarah Igo’s sharp and surprisingly lively “The Averaged American: Surveys, Citizens, and the Making of a Mass Public” (Harvard, 408 pages, $35). Ms. Igo patiently documents how surveys came to exercise this grip on the American imagination.

Surveys entered American public life in earnest, Ms. Igo argues, with the publication, in 1929, of Robert and Helen Lynd’s pioneering study “Middletown.” The Lynds, amateur social scientists, wanted to record the mores of a “representative” American town. After rejecting south bend, Ind., for its “cultural diversity” — that is, blacks — they chose Muncie, Ind., and cataloged in cold blood the work habits, religious practices, and leisure activities of these Midwesterners. The idea was to present Muncie as a “mirror” in which the rest of America could see itself. The study, 500 pages of charts and graphs, was a huge best-seller.

H.L. Mencken said that reading “Middletown” was “as exhilarating as even the dirtiest of the new novels,” and he was right. The country’s appetite for surveys had been whetted, and soon pollsters like George Gallup and Elmo Roper were happy to serve up more. Gallup and Roper had made names for themselves by publicly challenging — correctly, it turned out — the prediction made by a wellknown national straw poll for the 1936 presidential election. They brought new methods to the tabulation of public opinion. Scientific sampling allowed them to register the public’s feelings with only a fraction of the responses previously thought necessary. And the one-on-one interview allowed them to reach populations missed by traditional opinion takers, who simply mailed out questionnaires to lists of automobile and telephone owners (in 1936, a not very representative population).

Pollsters were soon registering much more than the public’s opinion on upcoming elections. Gallup’s report, “America Speaks!,” appeared four times a week in more than 100 metropolitan newspapers and registered the “public’s mind” on all “the issues of the day.” These pollsters became Cold Warriors of a sort. Polling, said Roper, was “the greatest contribution to democracy since the introduction of the secret ballot.” Gallup boasted that polling “took the pulse of democracy” and distinguished democracy, in which “expressing himself is part of a citizen’s birthright,” from totalitarianism that relied on the “artificial creation of an apparent majority.”

Ms. Igo, however, shows that the public’s frenzied embrace of surveys cannot be explained solely by its commitment to some democratic birthright. Surveys also provided a level of psychological solace. They fed a hunger to belong, to see oneself as part of group that was in some sense “normal.” This was especially true of the Kinsey reports, an extensive, two-volume study of Americans’ sexual practices. The reports’ labyrinth of distribution curves offered a kind of antidote to the festering insecurity that one’s desires might be unique or perverse.

In the preface to his “Sexual Behavior in the Human Male,” Kinsey noted that the most frequent questions interviewees had for his researchers involved “comparisons of [his or her] activities with averages for the group to which he belonged” and the question ‘Am I normal?'” Kinsey’s methods, to be sure, left much to be desired. Though he boasted of having included, in his study, the sexual habits of “thieves and hold-up men,” “bootleggers,” and “ne’erdo-wells” alongside “clergymen,” “farmers,” and “persons in the social register,” he, like the Lynds, failed to include “Negro groups” in the final tabulations.

This is an excellent, thoroughly readable book, but I fear that Ms. Igo never squarely faces up to a complex question invited by her title. Is the deification of public opinion an American phenomenon or a feature of large, lonely, industrial societies generally? Ms. Igo answers this somewhat obliquely, noting in passing that surveys flourished here in ways “unfathomable in Europe,” and that it seem a peculiarly American fantasy to imagine that “empirical surveys” could “disclose the society to itself.” In this, Ms. Igo agrees with Tocqueville, who predicted early on that the American republic would be particularly vulnerable to the tyranny of public opinion.

A second, more interesting question is why America proved so vulnerable to polls. For this question, Ms. Igo has no answer. But Tocqueville did, and so did John Stuart Mill in his review of “Democracy in America”:

The law above them, which older societies have found in the traditions of antiquity or in the dogmas or priests or philosophers, the Americans find in the opinions of one another. All being nearly equal in circumstances, and all nearly alike in intelligence and knowledge, the only authority which commands an involuntary deference is that of numbers.

America, then, was hard-wired, by virtue of its peculiar history — or, rather, lack of history — to be dominated by public opinion. The “Averaged” Frenchman may well exist, but the French, full of the “traditions of antiquity,” have no need for him. Perhaps this accounts for Ms. Igo’s sang-froid about public opinion’s ever-expanding domain. If there was nothing Americans could do, why lament it?

It’s hard to read Ms. Igo’s story without getting bewildered at this country’s pathology for surveys. Ms. Igo reproduces one of the poll’s George Gallup distributed in 1939, soliciting American opinion on pensions, World War II, and the American Communist Party. Interviewees were asked questions like “About how many members would you guess there are in the Communist party in the United States?” How can anything valuable can come from tabulating responses to this question? What would it allow us to say? That the “averaged American” “guesses” that there are 30,000 members of the American Communist party? This is as useless, really, as the fact that Americans think Cubans will be better off once Castro’s dead.

If we want to know what will happen in Cuba, what we should do is ask some experts — people who actually know something about the country, its history, and its mores. But, as Mill said, Americans believe that they are all roughly equal in intelligence and knowledge. Whether or not this belief is correct, Americans surely hold it. And so long as they do, surveys will be valued over experts — not merely as a way of registering public opinion but as a way of deciding what to do. Ms. Igo tells the story of a man who wrote to George Gallup in response to a survey Gallup carried out asking about the “most favorable climate” in America. This man got it right. “I’m not in the poll business,” he began, almost apologetically, “but If I were to make a report on cities with the best climates I would not ask people.” Who, then, would he ask? The Weather Bureau.

Mr. Boyle last wrote in these pages on the critic Lee Siegel.