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Polling Not an Exact Science

By John Brennan
Los Angeles Times


The latest round of presidential pre-election surveys has produced a flurry of seemingly contradictory findings, with Democrat Bill Clinton holding anything from a two-point to a 10-point lead. A lot of the difference may be due less to shifting voter allegiances than to the educated guesses of the polling mandarins about who is likely to vote.

It is estimated that about two-thirds of Americans are registered to vote but just about half of the public actually voted in the 1988 presidential election. The challenge is to identify those who are actually registered -- and those who will really cast ballots.

Pollsters generally identify registered voters by asking a respondent if he or she is enrolled to vote. That is only an estimate, because some people tend to say that they are registered even if they aren't.

Finding the elusive, smaller group of "likely" voters is tougher. It takes an additional series of questions that attempt to gauge people's interest in and knowledge of the election, their commitment to their candidate and whether they have voted in the past. Based on the answers to these inquiries, participants are graded as "likely" or "not likely" to vote.

Pollsters will often check the demographics of their "likely voter" samples against exit polling statistics from past elections, to see if they are correctly representing the shares of men and women, whites and blacks and young and older people who have traditionally turned out. Some may even verify whether the people in their sample are registered.

This is not exact science. There is no industry standard for determining likely voters; different sets of questions and different scoring techniques are used for deciding who will and who won't vote. And all this is based on what people say they do and feel, rather than on solid facts. Finally, though pollsters are fairly skilled at finding those who have voted in the past, they do less well at estimating the potential effects of younger, newer members of the electorate.

That's what is complicating the pollsters' job this year. Registration data and absentee voter requests from across the country suggest heightened interest in next week's presidential race, suggesting a turnout well above 1988 when half of all eligible voters cast ballots. Poll data support that conclusion: a mid-October Los Angeles Times survey four years ago found that 45 percent of voters said they were very interested in the presidential election. In the latest poll that figure is 64 percent. Just 36 percent of young adults were following the Bush-Dukakis contest closely in 1988. Now, 54 percent express such sentiments.

Another factor making the polls look more different than they are is the overemphasis on minor differences in the point spread. A spread of seven points between Clinton and Bush may look dramatically different than an 11-point margin, but from a statistical standpoint they are virtually the same. Take, for example, the Los Angeles Times Poll's survey of likely voters, released Wednesday: Clinton was at 44 percent, Bush 34 percent, and the sampling error was plus or minus 3 points. So Clinton's number actually could be anywhere from 41 percent to 47 percent, and Bush's somewhere between 31 percent and 37 percent.

All this is critical because the size of Clinton's lead seems to depend largely on how many of those untested but enthusiastic younger people pollsters allow through their "likely voter" window. Among the bigger unscreened pool of registered voters, Clinton has a generally wider and more consistent lead. Imposing a very tight screen on potential voters narrows the gap. Will those people turn out? While pollsters argue and point spreads open and close, only next week's vote count will tell.

Brennan is director of the Los Angeles Times Poll.