When is an opinion really an opinion? Not as often as many pollsters might think, says John M. Benson, managing director of the Harvard Opinion Research Program at the Harvard School of Public Health.Even on such presumably hot-button issues as school vouchers and charter schools, large proportions of Americans will acknowledge they really don't know enough about major issues in the news to venture an opinion. Or at least they'll acknowledge their ignorance if pollsters will let them-which they too often don't, Benson writes in the current issue of Public Perspective.An experiment in a 1999 survey by the Henry J. Kaiser Family Foundation, National Public Radio and Harvard showed just how large those effects can be. Half the respondents were asked standard 'favor or oppose' questions about school vouchers and charter schools, and the questioners recorded a 'don't know' response only if respondents volunteered it. The other half received parallel questions with the added phrase, '. . . or haven't you heard enough about that to have an opinion?'On the voucher questions, 'the 4 percent volunteered 'don't know' response ballooned into a 33 percent explicit 'haven't heard enough,' ' Benson wrote. But the charter school results were 'even more striking,' he reported. 'While only 9 percent volunteered 'don't know' in the standard favor/oppose version, 63 percent in the other form said they had not heard enough to have an opinion.'These results had consequences. When offered the chance to say they didn't know, the proportion supporting charter schools 'plunged' from a clear 62 percent majority to a mere 25 percent, 'presenting policymakers with two completely different pictures of the public's view.'Benson cites other evidence suggesting the prevalence of non-opinions about vouchers or school choice.The Washington Post, Kaiser Foundation and Harvard asked respondents in a poll last year if they knew what the term 'school voucher' meant, and 44 percent of all registered voters acknowledged that they did not. Likewise, about half of all Americans surveyed in a 2000 Phi Delta Kappa/Gallup survey said they had not heard, read or about charter schools.So why don't all pollsters automatically add a 'don't know' option to every question they ask? Part of the reason is that we don't want to make it too easy for people to answer 'don't know' to every question.But there's another reason. Nature abhors a vacuum, and media pollsters abhor a question that elicits a large percentage of Americans who decline to offer a view. So we force them to give an opinion in two ways. First by not explicitly offering a 'don't know' option in the language of the question that respondents are read. And then we 'lean' or otherwise prod respondents who initially say they don't have an opinion into offering one by suggesting that 'there are no right or wrong answers' or 'which view comes closest to your opinion.' Then and only if the respondent persists in telling the interviewer they do not have a view is a 'don't know' response coded.Such gentle nudges might be legitimate ways to get shy respondents to answer sensitive questions. The problem, though, is they often force people to create-on the spot-an opinion they otherwise don't have.But it rarely goes that far. That's because people feel obliged to answer a question when it is asked, even if they have no real opinion. And if they are not explicitly offered some version of 'I don't know' as an opinion, they pick from their choices-and an pseudo-opinion is born.A famous polling experiment illustrates the prevalence of these pseudo-opinions: More than 20 years ago, a group of researchers at the University of Cincinnati asked a random sample of local residents whether the 1975 Public Affairs Act should be repealed. About a third expressed a view one way or another-even though there never was a Public Affairs Act of 1975.I duplicated that experiment five years ago in a national survey, and obtained about the about the same result: Forty-three percent expressed an opinion, with 24 percent saying it should be repealed and 19 percent saying it should not. In another test, I took the experiment one step further. Half the randomly selected survey respondents were asked this question: 'President Clinton said that the 1975 Public Affairs Act should be repealed. Do you agree or disagree?'The other half of the respondents were asked this version of the question: 'The Republicans in Congress said that the 1975 Public Affairs Act should be repealed. Do you agree or disagree?'The partisan clues worked. More than half of those interviewed-53 percent-expressed an opinion, or 10 points more than the proportion with an opinion to the question version that didn't contain a partisan cue.And something else interesting happened. When Clinton was mentioned in the question as favoring repeal, 36 percent of the self-described Democrats interviewed agreed with Clinton to sink the Public Affairs Act, compared to just 16 percent of the Republicans in the sample.But when respondents learned from the question wording that Republicans in Congress favored repeal, the numbers were reversed: 36 percent of all Republicans but just 19 percent of all Democrats said they too favored repeal of the 1975 Public Affairs Act.

Richard Morin is director of polling for The Washington Post.