I make a big point on this blog of highlighting the importance of the fundamentals in determing the outcomes of presidential elections. Andrew Gelman has a nice graph illustrating how the fundamentals become more relevant as the election approaches (I've added a red arrow illustrating how far out we are from election day right now):
We should expect to see this process continuing in the next few weeks. As UW-Milwaukee's Tom Holbrook points out, one of the key effects of conventions is to bring the polls closer to the expected outcome:
[C]andidates who are running ahead of where they "should" be (based on the expected election outcome) tend to get smaller bumps, and those running behind their expected level of support get larger bumps. In this way, the conventions help bring the public closer to the expected outcome and help to make elections more predictable.
On the other hand, the fundamentals seems pretty closely aligned with current polls so it's not clear how much either candidate will gain from the conventions. Leading models forecast that Obama will receive 51.5-53% of the two-party vote and he's currently at 50.8% in the Pollster.com estimate. At the most, we might expect a small net gain for Obama (i.e. a slightly larger convention bump).
Has Andrew Gelman considered the variability within his model? The magnitude of the change was only around 0.2%.
The scale makes it look as if there was a dramatic change in the last 100 days. However, another way to view that graph would be that there was essentially no change during that period.
Posted by: David | August 21, 2008 at 02:33 PM
I agree with David. I think the graph is a bit difficult to interpret. The number of data points before day 120 are too sparse to be statistically significant and in the final 20 days the variance goes through the roof. Throw out the last 3 data points and it looks like the trend would remain nearly flat.
Couldn't we as easily interpret this as meaning that something significant happened in the last few days of the election?
Posted by: Jinchi | August 21, 2008 at 04:51 PM