More Numbers Crunched from SUSA State-by-State Polling

[Joanne98]

by Jonathan Singer, Sun Mar 16, 2008 at 12:40:17 PM EST

Earlier this month, SurveyUSA released state-by-state polling pitting John McCain against either Barack Obama or Hillary Clinton. In each state, SUSA surveyed 600 voters, so in total, 30,000 voters were interviewed for this massive project. This weekend over at Pollster.com, Professors Robert S. Erikson and Karl Sigman of Columbia University run further statistical analyses on these numbers and come up with some interesting results.


What do our results show? First, we pooled the state polls to ascertain the national vote, weighing each state's percent in proportion to the size of its House delegation. We also assign the District of Columbia as a 436th district and assign each Democratic candidate 85 percent of the vote to McCain's 15 percent. With these assumptions, the national popular "vote" is tight as of late February. Obama wins 51.5 percent versus McCain's 48.5 percent. Clinton also wins by an even razor thin margin, 50.7 to 49.3. With 30,000 cases, both estimates are statistically significant. McCain would be in the actual popular vote lead less than one time in 20.

That being said, our simulations yield a 88% chance of Obama beating McCain (with 306 Electoral College votes on average versus 233 for McCain), and a 74% chance of Hillary beating McCain (with 285 Electoral College votes on average versus 253 for McCain). About one percent of our simulated outcomes were Electoral College ties. (We ignored within-state variation in Maine and Nebraska, which divide their electoral votes by district.)

On the one hand, we find the expected numbers of electoral votes (the average from the simulations) for Obama or Clinton to be slightly higher than SurveyUSA reports. On the other hand, there is sufficient variance in the outcomes, so that McCain wins a nontrivial portion of the simulations, even with Obama as the opponent. Our two million simulations remind us that the popular vote winner is not always the Electoral College winner, although probably due mainly to chance -- the lottery aspect of the Electoral College -- and not any identifiable partisan bias in the 2008 Electoral College.


It would be wrong to think on the basis of these numbers that the Democrats necessarily have a 74 percent or even 88 percent chance of landing the presidency this fall. While SurveyUSA has done a very good job at pegging results in recent years and their numbers largely pass a smell test for validity, these numbers come a long way away from election day. With so many intervening events to come -- we cannot even begin to think what effect a brokered convention might have on the overall populace -- and the great likelihood that voters will become even more interested and knowledgeable about the campaigns, numbers will undoubtedly shift between the early spring and the late fall.

That said, these numbers are at least comforting at a time when a lot of folks are exceedingly willing to write this election off already as yet another in a long series of disappointments for the Democrats. If we do not allow ourselves to be divided, we truly have a great opportunity to win in 2008 -- and in fact to win with more than 50.1 percent of the popular vote for the first time in more than 40 years. So the time is not now to take our eyes off the ball.
http://www.mydd.com/story/2008/3/16/114810/718