Presidential elections are poll-driven. The candidate ahead in the surveys usually gets better coverage, and the results energize supporters. The one behind often comes across as doing little right, and campaigns and constituencies lose confidence. But what if the polls are wrong, and we aren't surveying the real likely electorate? This might be more than an academic issue. A number of polls this presidential race show a gap in the preferences of registered voters vs. likely voters. In these models, the president usually does better with likely voters, the figure most news organizations emphasize. To get to likely voters, all polling organizations use what is called a "screen," asking questions to determine who is likely to actually turn out on election day. [more
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