The Washington Post mega-poll is not predictive in an election context
The Washington Post commissioned a poll of all registered voters and decided to draw conclusions about who holds an electoral advantage from the results. The problem for the Washington Post, and they undoubtedly know this, is that polls of all registered voters always heavily favor Democrats and skew the results in such a way that they are ineffective in determining a likely winner. It may be useful in determining public opinion of registered voters, but who cares about that when we are talking about who will actually win? We want likely voters' opinions.
The Survey Monkey poll weighted the results to match "demographic characteristics of registered voters in each state," rather than typical voter turnout models. Elections are not decided by a demographically representative pool of registered voters. If that were the case, the Democrats would win every national election because there are more registered Democrats. The problem for Democrats is that they have a big problem getting their voters to actually turn out and vote, and that is true every time.
Republicans do better in off-year elections because their voters turn out, even when the national focus is not on politics. Democrats do better in presidential years because so much attention is paid to politics. But even in a presidential year, only 60% of the potential electorate will turn out and vote.
The Washington Post's pollster is not filtering for who is likely to vote. What this method of polling achieves is a built-in bump for any Democrat, usually a big one. Nate Silver demonstrates the statistical bias towards Democrats in both presidential and non-presidential election years.
One need not delve into the statistics to see the invalidity of this type of poll for determining who will win fifty state elections. One need only look at the results to find that the poll is not predictive.
The Washington Post poll found that Trump is tied with Hillary in Mississippi and Texas. There is no chance that Hillary will win either state. There simply are not enough NeverTrumpers in the GOP to accomplish this task. But in the imaginary world the Washington Post created, that could happen.
This poll does accomplish one thing, however, something WaPo would not have wanted to demonstrate. Because Trump is running even or ahead in a number of normally Democratic states even when the sample is skewed to favor Democrats, it demonstrates that Trump has real strength in those states.
Clinton +2.1 Points in All Ref Battlegrounds (Trump +0.4 from last result)
Clinton +1.9 Points in Traditional GOP States (Trump +0.2 from last result)
Registered voter polls, as opposed to likely voter polls, always favor Democrats
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