Hanging on the wall of the National Press Club’s Truman Lounge is a testament to the fallibility of polling. It’s the famous photo of a triumphant President Harry S. Truman waving a copy of the Chicago Tribune with the banner headline, “Dewey Defeats Truman” two days after the 1948 election.
It was perhaps the first big flop for predictive polling in American politics. It wouldn't be the last.
This is not to suggest that scientific polling properly conducted is a waste of time, because it’s not. Polling can give an indication of what might happen in a future election, and in many cases it’s reasonably accurate. But sometimes, such as in the March 8 Michigan primary elections for Democratic and Republican presidential candidates, they can also be very wrong.
In the case of Michigan, the polls had Bernie Sanders losing to Hillary Clinton by at least 11 percent. Some polls predicted a larger margin. Yet Sanders pulled out a narrow win.
Likewise, while the polls correctly predicted that Donald Trump would win the primary election for the Republicans, they did not predict that former Ohio governor John Kasich would virtually tie Senator Ted Cruz for second in the delegate count. Nor did the polls suggest that Senator Marco Rubio would finish a distant fourth.
Part of the problem with polling, as it’s performed by the news media and by campaign organizations, is that it’s not happening in real time. This means that poll results that are released on a Monday will probably reflect contact with potential voters sometime in the previous week. At best, they reflect voter sentiment as it was perhaps days in the past.
Another part of the problem is that the polling doesn’t necessarily reflect reality, at least in terms of what a specific voter might do when it’s actually time to cast a ballot. There are several reasons for this lack of accuracy.
First, poll participants lie. Really, they don’t necessarily tell the pollster what they really believe or what they might actually do when it comes to voting or purchasing a product.
Sometimes the lack of truthfulness is because the person doesn’t actually know the answer, but doesn’t want to admit that. Or the voter in an election poll might change their mind not even having a clear idea of who the candidates are. Or, their choice isn’t available, so they make up an answer since they can’t choose Jeb Bush or Lindsay Graham, for example, when the poll is performed.
And sometimes, for whatever reason, the polling subject doesn't want to truthfully say who their favorite really is. They might say they are undecided, for example, when they’re not. The reasons range from feeling that it’s not the pollster’s business to wanting all the attention that goes with being an undecided voter in a swing state.
There are other reasons. Polling organizations make an adjustment to the results to reflect the levels of participation they think will take place. This is what happened in polls preceding the Democratic primary in Michigan in which some pollsters discounted the under-35 vote as being unlikely to show up.
In fact, those younger voters did show up in large numbers, according to the exit poll data shared by the broadcast organizations covering the election, and the fact that, Sanders, who consistently polls well among younger voters, won him the Michigan primary much to the surprise of all the political prognosticators who expected a big win by rival Hillary Clinton.