Mitt Romney is poised to capture an easy victory tonight in the Illinois primary. The prediction markets currently give the former governor a 97.4 percent chance of winning the state, with Rick Santorum trailing at just 3.2 percent. We've seen Santorum overcome long odds before, but not at this steep of a disadvantage going into the day.
The following chart shows the progression of our forecasts, compared with the poll-based forecast that the New York Times' Nate Silver publishes on the FiveThirtyEight blog:
Sources: Betfair, Intrade and FiveThirtyEight
Normally we can point to some major event that caused our forecast to jump when we see this sort of precipitous climb in a candidate's prospects, but Romney's ascend in the Illinois primary odds has been more of a solid progression. The polls and other information from Illinois have been a slow trickle of increasingly positive news for him. Even without any change to the situation on the ground, we observed on March 14, the likelihood of Romney's victory steadily increased as the election grew closer and Santorum failed to gain much traction in the state.
As Romney inches higher in the delegate count, the race becomes even more certain. The markets now give Mitt Romney an 88.9 percent likelihood of ultimately capturing the nomination.
David Rothschild is an economist at Yahoo! Research. He has a Ph.D. in applied economics from the Wharton School of Business at the University of Pennsylvania. Follow him on Twitter @DavMicRot and email him at firstname.lastname@example.org.
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