Posted by Dan McLaughlin (Diary)

In a long election season, it’s never wise to get too high or too low over any one poll. Presidential elections are won at the state level, but statewide polling is fairly sporadic at this stage of the race, so we’re stuck reading national polls a lot. But the latest poll is bad news for President Obama.

We all know the major issues by now to look for with individual polls: some polls are adults, and are totally useless, because only registered voters can vote. Polls of likely voters, in turn, are vastly more accurate and less Democratic-biased than polls of registered voters, many of whom also don’t show up to vote. Most polls are also reported after weighting to achieve some guesstimate of the partisan breakdown of the general electorate among Democrats, Republicans and Independents. Even polls that don’t feature egregious hackery are an inexact science, because they rest on the pollster’s current assumptions about the D/R/I split and the ‘screen’ they use to decide who is a likely voter. If the shape of the electorate is not as projected, the poll will be wrong.

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