Obama up by 3.2%; 77% chance of victory

Commentary

Obama has widened his lead by about 1.5%, and about half of his new votes are from Undecided. This suggests to me that the Clinton supporters who told pollsters they were undecided while the primaries were ongoing have now come home to the Democratic nominee.

Prediction for Election Day

• Probability of victory: 78% electoral, 77% popular. This includes a 1% chance of tie.
• Expected value of vote: 306 electoral votes, popular win by 1.1%.
• 95% range of electoral votes: 192 to 410.
• Swing states (pseudo-Banzhaf):
  • PA .055
  • MI .034
  • OH .033
  • NM .021
  • NV .013
  • CO .010
• Swing states (correlation):
  • 80%+ PA
  • 70%+ OH, MI
  • 60%+ NH
  • 50%+ NM, NV, MO
  • 40%+ CO, WI, VA, NJ
• Confidence map (states sized by electoral vote, darker red means higher confidence that McCain will win, darker green for Obama):

Prediction if the election were today

• Probability of victory: 99% electoral, 100% popular. This includes a <0.5% chance of a tie.
• Expected value of vote: 308 electoral votes, popular win by 3.2%.
• 95% range of electoral votes: 274 to 349.
• Swing states (pseudo-Banzhaf):
  • PA .010
• Swing states (correlation):
  • 50%+ PA
  • 30%+ MI
• Confidence map (states sized by electoral vote, darker red means higher confidence that McCain will win, darker green for Obama):

Popular vote estimate

(Darker red means more votes for McCain, darker green for Obama.)

Technical note

I increased my volatility parameter to assume 3.8% annual volatility in each candidate's national popular vote share, up from 2.7%. This is more in line with observed volatility this year. The effect of this is that more recent polls will have more weight, and that the election-day forecasts will be more uncertain (i.e., the expected probability of victory for each candidate will be closer to 50% than previously, all else equal).