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FiveThirtyEight

Politics

I thought this was a poll-less day in so far as general election matchups go, but we do have a couple.

Firstly, in Washington, Survey USA has Obama leading by 7, but Clinton trailing by 1, against John McCain. These results are quite consistent with other polling we’ve seen in Washington, and not otherwise noteworthy.

Secondly, in Pennsylvania, a commenter tipped us to a new Strategic Vision poll, which, while it contains relatively good news for Obama in the primaries, shows Clinton faring much better in the general election (+3 versus -7). The general election numbers are a near-match for Strategic Vision’s 3/29 poll of Pennsylvania, which showed Clinton leading McCain by 6 points but Obama trailing him by 5. A couple of additional notes/comments after the break.

#1. A number of people have asked me what I think about the primary polls in Pennsylvania; I think you should all read Mark Blumenthal. I don’t particularly believe that there’s actually been movement toward Clinton; Survey USA seems to show that, but three or four other pollsters show continued movement toward Obama. I do believe it’s possible that Survey USA’s turnout model, which seems more pessimistic for Obama, may be closer to the mark. In particular, their 58/42 female/male split seems highly consistent with previous primaries, and perhaps more reasonable than the 54/46 split they had before. However, their estimate of 14% African-American turnout may be low. The general rule of thumb is that African-American turnout in a Democratic primary is about 175% of the state’s African-American population as a whole, which would imply turnout closer to 18 or 19%.

EDIT:Actually, the ratio is closer to 150% than 175%. So, Survey USA’s estimate is not unreasonable. More on this in a moment.

#2. (Technical) I’ve made a slight adjustment to the ‘recentness factor’ based on some testing of previous election results that I’ve done. The half-life for discounting polls is now set at 30 days, regardless of the number of days until the election. I owe you guys a more thorough explanation on this and a couple of other things, but basically — this turns out to be just as accurate as the method I’d been using before (actually, a little bit more so), and it has the virtue of being less complicated. The practical upshot of this for the time being is that older polls are discounted somewhat more heavily.

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