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“The Myth of the Incumbent 50% Rule”

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Illinois
Polls

1) It is extremely common for an incumbent come back to win re-election while having less than 50 percent of the vote in early polls.

2) In comparison to early polls, there is no demonstrable tendency for challengers to pick up a larger share of the undecided vote than incumbents.

3) Incumbents almost always get a larger share of the actual vote than they do in early polls (as do challengers). They do not “get what they get in the tracking”; they almost always get more.

4) However, the incumbent’s vote share in early polls may in fact be a better predictor of the final margin in the race than the opponent’s vote share. That is, it may be proper to focus more on the incumbent’s number than the opponent’s when evaluating such a poll — even though it is extremely improper to assume that the incumbent will not pick up any additional percentage of the vote.

Go read the rest for his research.

posted by Rich Miller
Friday, Oct 17, 14 @ 9:38 am

Comments

This paragraph was interesting:

It is probably OK to focus on an incumbent’s vote share in early polls while downplaying the challenger’s number, but if you do, you need to add 6-7 percent to it to have the most accurate prediction of his likely performance in November. In Strickland’s case, for instance, polling at 44 percent in the early polls would predict a final vote share of 50-51 percent.

Comment by Illannoyed Friday, Oct 17, 14 @ 10:02 am
It’s good to have up-to-date research so we can more accurately assess poll data.

Comment by anon Friday, Oct 17, 14 @ 10:07 am
Nate Silver is really, really good at what he does. ESPN hiring him was a coup. He is one of those guys that you can’t be mad at because he merely uses statistics and trends to make predictions. He is the antithesis of a talking head on Fox, CNN or MSNBC.

Comment by Team Sleep Friday, Oct 17, 14 @ 10:30 am
Note: He is talking about early polls, those between January and June.

The actual results versus later polls are mixed.

Comment by walker Friday, Oct 17, 14 @ 11:19 am