Post Mortem: 9am, November 6
It looks like Trump will take all the swing states. He won Michigan and all the states ranked below Michigan, consistent with the ranking assumption. Note that the betting markets were off for Michigan and Wisconsin in that they had a probability above 50 percent that Harris would win, but this does not affect the ranking assumption.Background
Predictit no longer has probabilities by states, but Smarkets, Betfair, and Polymarket do. The Betfair and Polymarket probabilities sum to 100, but the Smarkets probabilities do not. For Smarkets, the following was done. Let Di be the Smarkets probabiity that the Democrats win state i, and let Ri be the Smarkets probability that the Repubicans win state i. The Democratic probability was then taken to be Di/(Di + Ri).There are 8 states in play for the 2024 presidential election. Table 1 lists in alphabetic order the states assumed to go Democratic, the 8 swing states, and in alphabetic order the states assumed to go Republican. The swing states are ranked by the Smarkets probability for the Democrats. The Betfair probabilities are in parentheses, and the Polymarket probabilities are in brackets. The following is a discussion of the data.
Data collected from Smarkets, (Betfair), and [Polymarket] at 7:00pm EST on November 4, 2024
The 8 swing states are:
| state | prob | votes | sumvotes | |
| Michigan | 65.0 (65) [61] | 15 | 241 | |
| Wisconsin | 57.2 (59) [57] | 10 | 251 | |
| Pennsylvania | 46.5 (47) [42] | 19 | 270 | pivot |
| Nevada | 45.1 (47) [44] | 6 | ||
| Georgia | 35.3 (36) [35] | 16 | ||
| North Carolina | 33.8 (34) [33] | 16 | ||
| Arizona | 26.1 (25) [25] | 11 | ||
| Florida | 9.2 ( 7) [ 6] | 30 | ||
41.9, (41.0), [41.5] = Smarkets, (Betfair), [Polymarket] market probability that the Democrats win the presidential election.
"sumvotes" is the sum of the electoral votes of all the states ranked above the state plus the state's vote. (See Table 1.) 270 votes are needed to win. You can see that Pennslyvania is the pivot state using Smarkets (and the other two). If the Democrats take Pennsylvania and all the states ranked above it, they get 270 votes (assuming 1 vote from Nebraska). Of the states ranked below Pennsylvania, the Democrats could also win by not taking Pennsylvania, but, say, taking Nevada and Georgia. This would, of course, violate the ranking assumption.
According to the ranking assumption, the probability that the Democrats get a majority in the electoral college is the probability that they win the pivot state, Pennslyvania, which is 46.5 for Smarkets. The Smarkets market probability that the Democrats win the presidential election (in the electoral college) is 41.9, smaller than 46.5. For Betfair the market probability is 41.0, which compares to 45 for the Betfair Pennsylvania probability. For Polymarket the market probability is 41.5, which compares to 42 for Polymarket Pennslyvania probability. For all three markets the market probability is thus slightly lower than the ranking probability, although for Polymarket it is essentially the same.
The probabilities for the Democrats are generally up from those that existed on October 22, 2024, below.
I also compiled the probabilites for the Kalshi betting market. The pivot state is also Pennsylvania, with a probability of 45. The overall market probability for Kalshi is 46, higher than the other three, but essentially the same as the ranking probability using Kalshi.
Data collected from Smarkets, (Betfair), and [Polymarket] at 7:00pm EDT on October 22, 2024
The 8 swing states are:
| state | prob | votes | sumvotes | |
| Michigan | 46.0 (46) [41] | 15 | 241 | |
| Pennsylvania | 45.6 (43) [39] | 19 | 260 | |
| Wisconsin | 44.3 (47) [43] | 10 | 270 | pivot |
| Nevada | 43.2 (42) [37] | 6 | ||
| North Carolina | 33.0 (32) [30] | 16 | ||
| Georgia | 33.0 (34) [29] | 16 | ||
| Arizona | 28.7 (26) [26] | 11 | ||
| Florida | 9.0 ( 9) [ 6] | 30 | ||
39.1, (37.9), [35.9] = Smarkets, (Betfair), [Polymarket] market probability that the Democrats win the presidential election.
"sumvotes" is the sum of the electoral votes of all the states ranked above the state plus the state's vote. (See Table 1.) 270 votes are needed to win. You can see that Wisconsin is the pivot state using Smarkets. If the Democrats take Wisconsin and all the states ranked above it, they get 270 votes (assuming 1 vote from Nebraska). Of the states ranked below Wisconsin, the Democrats could also win by not taking Wisconsin, but, say, taking Georgia or North Carolina. This would, of course, violate the ranking assumption. For Betfair and Polymarket the pivot state is Pennsylvania, with probabilities of 43 and 39, respectively.
According to the ranking assumption, the probability that the Democrats get a majority in the electoral college is for Smarkets the probability that they win the pivot state, Wisconsin, which is 44.3. The Smarkets market probability that the Democrats win the presidential election (in the electoral college) is 39.1 for Smarkets, smaller than 44.3. For Betfair the market probability is 37.9, which compares to 43 for the Betfair pivot state, Pennsylvania. For Polymarket the market probability is 35.9, which compares to 39 for the Polymarket pivot state, Pennslyvania. For all three markets the market probability is thus lower than the probabiity of the pivot state.
The probabilities for the Democrats are down from those that existed on October 8, 2024, below.
Data collected from Smarkets, (Betfair), and [Polymarket] at 5:30pm EDT on October 8, 2024
The 8 swing states are:
| state | prob | votes | sumvotes | |
| Michigan | 57.6 (58) [54] | 15 | 241 | |
| Wisconsin | 56.4 (57) [53] | 10 | 251 | |
| Nevada | 56.0 (56) [52] | 6 | 257 | |
| Pennsylvania | 51.6 (49) [44] | 19 | 276 | pivot |
| North Carolina | 40.5 (41) [40] | 16 | ||
| Georgia | 38.1 (37) [36] | 16 | ||
| Arizona | 35.0 (32) [33] | 11 | ||
| Florida | 15.7 (14) [11] | 30 | ||
50.0, (48.9), [46.7] = Smarkets, (Betfair), [Polymarket] market probability that the Democrats win the presidential election.
"sumvotes" is the sum of the electoral votes of all the states ranked above the state plus the state's vote. (See Table 1.) 270 votes are needed to win. You can see that Pennsylvania is the pivot state. If the Democrats take Pennsylvania and all the states ranked above it, they get 276 votes (assuming 1 vote from Nebraska). Of the states ranked below Pennsylvania, the Democrats could also win by not taking Pennsylvania, but, say, taking North Carolina or Georgia. This would, of course, violate the ranking assumption.
According to the ranking assumption, the probability that the Democrats get a majority in the electoral college is the probability that they win the pivot state, Pennsylvania, which is 51.6 for Smarkets, 49 for Betfair, and 44 for Polymarket. The market probability that the Democrats win the presidential election (in the electoral college) is 50.0 for Smarkets, slightly lower than 51.6. For Betfair the two numbers are 48.9 and 49. For Polymarket the two numbers are 46.7 and 44. It is thus roughly the case that the behavior of the market participants is consistent with their using the ranking assumption.
It is interesting that the probabilities for the Democrats are generally down from those that existed on September 24, 2024. Also, Betfair and Polymarket now have less that 50 percent probability for the Democrats.
Data collected from Smarkets, (Betfair), and [Polymarket] at 5pm EDT on September 24, 2024
The 8 swing states are:
| state | prob | votes | sumvotes | |
| Michigan | 65.0 (66) [68] | 15 | 241 | |
| Wisconsin | 62.3 (63) [58] | 10 | 251 | |
| Pennsylvania | 54.3 (53) [52] | 19 | 270 | pivot |
| Nevada | 51.6 (53) [51] | 6 | ||
| Georgia | 41.7 (39) [38] | 16 | ||
| North Carolina | 40.9 (43) [44] | 16 | ||
| Arizona | 39.4 (37) [37] | 11 | ||
| Florida | 12.2 (13) [15] | 30 | ||
52.3, (53.6), [51.0] = Smarkets, (Betfair), [Polymarket] market probability that the Democrats win the presidential election.
"sumvotes" is the sum of the electoral votes of all the states ranked above the state plus the state's vote. (See Table 1.) 270 votes are needed to win. You can see that Pennsylvania is the pivot state. If the Democrats take Pennsylvania and all the states ranked above it, they get 270 votes (assuming 1 vote from Nebraska). Of the states ranked below Pennsylvania, the Democrats could also win by not taking Pennsylvania, but, say, taking Nevada and Georgia. This would, of course, violate the ranking assumption.
According to the ranking assumption, the probability that the Democrats get a majority in the electoral college is the probability that they win the pivot state, Pennsylvania, which is 54.3 for Smarkets, 53 for Betfair, and 52 for Polymarket. The market probability that the Democrats win the presidential election (in the electoral college) is 52.3 for Smarkets, slightly lower than 54.3. For Betfair the two numbers are 53.6 and 53. For Polymarket the two numbers are 51.0 and 52. It is thus roughly the case that the behavior of the market participants is consistent with their using the ranking assumption.
Data collected from Smarkets and Betfair at 5pm EDT on September 11, 2024
The 8 swing states are:
| state | prob | votes | sumvotes | |
| Michigan | 60.2 (61) | 15 | 241 | |
| Wisconsin | 60.1 (60) | 10 | 251 | |
| Nevada | 50.6 (52) | 6 | 257 | |
| Pennsylvania | 49.5 (51) | 19 | 276 | pivot |
| Georgia | 42.0 (40) | 16 | ||
| Arizona | 39.2 (42) | 11 | ||
| North Carolina | 35.0 (42) | 16 | ||
| Florida | 11.9 (15) | 30 | ||
52.3 (51.4) = Smarkets (Betfair) market probability that the Democrats win the presidential election.
"sumvotes" is the sum of the electoral votes of all the states ranked above the state plus the state's vote. (See Table 1.) 270 votes are needed to win. You can see that Pennsylvania is the pivot state. If the Democrats take Pennsylvania and all the states ranked above it, they get 276 votes. Of the states ranked below Pennsylvania, the Democrats could also win by not taking Pennsylvania, but, say, taking Georgia. This would, of course, violate the ranking assumption.
According to the ranking assumption, the probability that the Democrats get a majority in the electoral college is the probability that they win the pivot state, Pennsylvania, which is 49.5 for Smarkets and 51 for Betfair. The market probability that the Democrats win the presidential election (in the electoral college) is 52.3 for Smarkets, higher than 49.5. For Betfair the two numbers are 51.4 and 51. The Betfair numbers are thus consistent with the market participants using the ranking assumption, but not Smarkets.