Forecasting
What to expect tomorrow
Nov 5th 2012, 15:47 by R.A. | WASHINGTON
TOMORROW Americans will go to the polls to select a new president. (Technically, they'll go to the polls to select a slate of "electors", who will in turn choose the president, because that's just how clever the founding fathers were.) Months—years actually—of intense polling on how Americans are likely to vote will finally be put to the test; have the pollsters been measuring opinion accurately or not?
New research from David Rothschild and Justin Wolfers suggests that however accurate the polling, it's less accurate than it could be if opinion firms asked different questions. In particular, they should worry more about what voters think will happen than what voters intend to do themselves:
We find robust evidence that polls probing voters’ expectations yield more accurate predictions of election outcomes than the usual questions asking about who they intend to vote for. By comparing the performance of these two questions only when they are asked of the exact same people in exactly the same survey, we effectively difference out the influence of all other factors...Our alternative approach to political forecasting also provides a new narrative of the ebb and flow of campaigns, which should inform ongoing political science research about which events really matter. For instance, through the 2004 campaign, polls of voter intentions suggested a volatile electorate as George W. Bush and John Kerry swapped the lead several times. By contrast, polls of voters’ expectations consistently showed the Bush was expected to win re-election. Likewise in 2008, despite volatility in the polls of voters’ intentions, Obama was expected to win in all of the last 17 expectations polls taken over the final months of the campaign. And in the 2012 Republican primary, polls of voters intentions at different points showed Mitt Romney trailing Donald Trump, then Rick Perry, then Herman Cain, then Newt Gingrich and then Rick Santorum, while polls of expectations showed him consistently as the likely winner.
The intuition behind the result is that expectations polls are tapping into a broader vein of information. Individuals responding to polls actually know much more about the election than just their own voting intentions. They also have a sense for how people across their social networks are leaning. Aggregating this broader information flow in a poll is more informative and useful than just collecting from respondents comparatively meagre data on how they intend to vote.
The logic is similar to that underlying prediction markets, for which Mr Wolfers is an evangelist. The authors note that prediction markets like Intrade often outperform inidividual polls and even forecasts built on skillfully aggregated polls. Participants in prediction markets not only provide their own assessment of the probable outcome of a question, but provide information weighted by conviction, measured monetarily.
As of this moment, Barack Obama is favoured to win across several betting markets and in polls of expectations. Most polls of voter intentions give Mr Obama a slight edge, but are comparatively unsure about the race; some continue to show a lead for Mitt Romney. And so tomorrow will provide a bit more information on how best to assess the state of critical political races.
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