Ranking Assumption for 2020 Presidential election Data collected from Predictit on September 8, 2020 On this date, 19 states had market probabilities on the Predictit website less than 90 percent and greater than 10 percent for the Democrats winning the state. The 19 states, ranked by market probabilities for the Democratic candidate, are:
 state prob votes sumvotes Maine not 02 82 3 212 Nevada 80 6 218 New Hampshire 71 4 222 Minnesota 70 10 232 Michigan 69 16 248 Nebraska 02 67 1 249 Wisconsin 65 10 259 Arizona 63 11 270 pivot Pennsylvania 63 20 290 pivot Florida 53 29 North Carolina 49 15 Ohio 36 18 Maine 02 36 1 Georgia 35 16 Iowa 31 6 Texas 29 38 Alaska 15 3 Missouri 12 10 Montana 12 3
 60 = Predictit market-based 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. 270 votes are needed to win. You can see that Arizona or Pennsylvania is the pivot state (they have equal probabilities). If Biden takes Arizona or Pennsylvania and all the states ranked above it, he gets 270 or 290 votes. Of the states ranked below Arizona and Pennslyvania, he could also win by not taking Arizona and Pennsylvania but taking Florida. This would, of course, violate the ranking assumption. There is evidence that traders are more or less using 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, Arizona or Pennslyvania, which is 63. On the Predictit website, the market-based probability that the Democrats win the presidential election (in the electoral college) is 60, close to 63. Data collected from Predictit on September 22, 2020 On this date, 19 states had market probabilities on the Predictit website less than 90 percent and greater than 10 percent for the Democrats winning the state. The 19 states, ranked by market probabilities for the Democratic candidate, are:
 state prob votes sumvotes New Mexico 89 5 200 Colorado 89 9 209 Maine not 02 86 3 212 Nevada 76 6 218 Minnesota 75 10 228 Michigan 72 16 244 New Hampshire 71 4 248 Wisconsin 66 10 258 Nebraska 02 65 1 259 Arizona 65 11 270 pivot Pennsylvania 64 20 Florida 48 29 North Carolina 47 15 Maine 02 47 1 Iowa 36 6 Ohio 34 18 Georgia 34 16 Texas 26 38 Alaska 16 3
 59 = Predictit market-based 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. 270 votes are needed to win. You can see that Arizona is the pivot state. If Biden takes Arizona and all the states ranked above it, he gets 270 votes. Of the states ranked below Arizona, he could also win by not taking Arizona, but taking Pennsylvania, Florida, or North Carolina. This would, of course, violate the ranking assumption. There is evidence that traders are more or less using 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, Arizona, which is 65. On the Predictit website, the market-based probability that the Democrats win the presidential election (in the electoral college) is 59, close to 65. Data collected from Predictit on October 6, 2020 On this date, 21 states had market probabilities on the Predictit website less than 90 percent and greater than 10 percent for the Democrats winning the state. The 21 states, ranked by market probabilities for the Democratic candidate, are:
 state prob votes sumvotes Minnesota 79 10 222 New Hampshire 79 4 226 Nevada 78 6 232 Nebraska 02 78 1 233 Michigan 77 16 249 Wisconsin 72 10 259 Pennsylvania 71 20 279 pivot Arizona 68 11 Maine 02 56 1 Florida 55 29 North Carolina 53 15 Ohio 44 18 Georgia 43 16 Iowa 41 6 Texas 31 38 Alaska 21 3 South Carolina 20 9 Missouri 14 10 Montana 13 3 Kansas 11 6 Indiana 11 11
 66 = Predictit market-based 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. 270 votes are needed to win. You can see that Pennsylvania is the pivot state. If Biden takes Pennsylvania and all the states ranked above it, he gets 279 votes. Of the states ranked below Pennsylvania, he could also win by not taking Pennsylvania, but taking Arizona, Florida, or North Carolina, where he is favored. 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 71. On the Predictit website, the market-based probability that the Democrats win the presidential election (in the electoral college) is 66, slightly below 71. So the market participants are not quite using the ranking assumption. Data collected from Predictit on October 20, 2020 On this date, 20 states had market probabilities on the Predictit website less than 90 percent and greater than 10 percent for the Democrats winning the state. The 20 states, ranked by market probabilities for the Democratic candidate, are:
 state prob votes sumvotes New Mexico 89 5 200 Colorado 89 9 209 Maine not 02 88 3 212 New Hampshire 78 4 216 Nebraska 02 77 1 217 Minnesota 76 10 227 Nevada 74 6 233 Wisconsin 68 10 243 Pennsylvania 68 20 263 Michigan 67 16 279 pivot Arizona 58 11 North Carolina 52 15 Florida 51 29 Maine 02 42 1 Georgia 41 16 Ohio 36 18 Iowa 33 6 Texas 29 38 Alaska 15 3 South Carolina 11 9
64 = Predictit market-based 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. 270 votes are needed to win. You can see that Michigan is the pivot state. If Biden takes Michigan and all the states ranked above it, he gets 279 votes. Of the states ranked below Michigan, he could also win by not taking Michigan, but taking Arizona, where he is favored. 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, Michigan, which is 67. On the Predictit website, the market-based probability that the Democrats win the presidential election (in the electoral college) is 64, close to 67. So the market participants are roughly using the ranking assumption.
 Ranking Assumption for 2020 Senate elections Data collected from Predictit on September 8, 2020 The current make up of the Senate is 53 Republicans and 47 Democrats, counting the 2 independents as Democrats. Only 14 states are in play in having market probabilities on the Predictit website less than 90 percent and greater than 10 percent. The 14 states ranked by the market probabilities from Predictit for the Democratic candidate are:
 state prob now Colorado 88 R Arizona 87 R Minnesota 84 D Michigan 77 D Maine 72 R pivot for 50 Democratic seats North Carolina 67 R pivot for 51 Democratic seats Iowa 45 R Montana 41 R Georgia, reg. 30 R Alaska 26 R South Carolina 23 R Georgia, spec. 20 R Texas 13 R Alabama 11 R
 56 = Predictit market-based probability of the Democrats controlling the Senate. If the Democrats win North Carolina and all the states above it, they will have 51 seats, counting the 2 independents as Democrats. If they win Maine and all the states above it but lose North Carolina, they will have 50 seats. They will still control the Senate if they win the White House. According to the ranking assumption, the Predictit market probablility that they control the Senate is thus 72 percent (the probablity they win Maine) if they win the White House and 67 percent (the probablility they win North Carolina) if they don't. If we use the Predictit market-based probabilty of 60 percent that the Democrats win the presidential electon, then the ranking assumption probability that the Democrats control the Senate is 0.60x72 + 0.40x67, which is 70 percent. This is noticeably higher than the Predictit market-based probability of the Democrats controlling the Senate of 56 percent. In this case, unlike in the Presidential case, it does not look like the market is using the ranking assumption. Data collected from Predictit on September 22, 2020 The current make up of the Senate is 53 Republicans and 47 Democrats, counting the 2 independents as Democrats. Only 16 states are in play in having market probabilities on the Predictit website less than 90 percent and greater than 10 percent. The 16 states ranked by the market probabilities from Predictit for the Democratic candidate are:
 state prob now Minnesota 87 D Colorado 84 R Arizona 83 R Michigan 73 D Maine 73 R pivot for 50 Democratic seats North Carolina 65 R pivot for 51 Democratic seats Iowa 49 R Montana 42 R Georgia, reg. 35 R South Carolina 30 R Georgia, spec. 27 R Alaska 26 R Kansas 22 R Texas 16 R Alabama 12 R Kentucky 11 R
 57 = Predictit market-based probability of the Democrats controlling the Senate. If the Democrats win North Carolina and all the states above it, they will have 51 seats, counting the 2 independents as Democrats. If they win Maine and all the states above it but lose North Carolina, they will have 50 seats. They will still control the Senate if they win the White House. According to the ranking assumption, the Predictit market probablility that they control the Senate is thus 73 percent (the probablity they win Maine) if they win the White House and 65 percent (the probablility they win North Carolina) if they don't. If we use the Predictit market-based probabilty of 59 percent that the Democrats win the presidential electon, then the ranking assumption probability that the Democrats control the Senate is 0.59x73 + 0.41x65, which is 70 percent. This is noticeably higher than the Predictit market-based probability of the Democrats controlling the Senate of 57 percent. In this case, unlike in the Presidential case, it does not look like the market is using the ranking assumption. Data collected from Predictit on October 6, 2020 The current make up of the Senate is 53 Republicans and 47 Democrats, counting the 2 independents as Democrats. Only 16 states are in play in having market probabilities on the Predictit website less than 90 percent and greater than 10 percent. The 16 states ranked by the market probabilities from Predictit for the Democratic candidate are:
 state prob now Colorado 87 R Arizona 83 R Maine 77 R pivot for 50 Democratic seats Michigan 71 D North Carolina 58 R pivot for 51 Democratic seats Iowa 54 R Montana 42 R Georgia, reg. 38 R Georgia, spec. 34 R Alaska 34 R South Carolina 32 R Kansas 31 R Mississippi 19 R Texas 18 R Alabama 13 R Kentucky 11 R
 66 = Predictit market-based probability of the Democrats controlling the Senate. If the Democrats win North Carolina and all the states above it, they will have 51 seats, counting the 2 independents as Democrats. If they win Maine and all the states above it but lose North Carolina, they will have 50 seats. They will still control the Senate if they win the White House. According to the ranking assumption, the Predictit market probablility that they control the Senate is thus 77 percent (the probablity they win Maine) if they win the White House and 58 percent (the probablility they win North Carolina) if they don't. If we use the Predictit market-based probabilty of 66 percent that the Democrats win the presidential electon, then the ranking assumption probability that the Democrats control the Senate is 0.66x77 + 0.34x58, which is 70.5 percent. This is somewhat higher than the Predictit market-based probability of the Democrats controlling the Senate of 66 percent. So the market is not quite using the ranking asssumption. Data collected from Predictit on October 20, 2020 The current make up of the Senate is 53 Republicans and 47 Democrats, counting the 2 independents as Democrats. Only 16 states are in play in having market probabilities on the Predictit website less than 90 percent and greater than 10 percent. The 16 states ranked by the market probabilities from Predictit for the Democratic candidate are:
 state prob now Minnesota 87 D Colorado 87 R Arizona 80 R Maine 76 R Michigan 64 D North Carolina 60 R pivot for 50 Democratic seats Iowa 60 R pivot for 51 Democratic seats Georgia, spec. 43 R Montana 37 R Georgia, reg. 37 R South Carolina 27 R Kansas 26 R Alaska 24 R Texas 23 R Mississippi 14 R Alabama 13 D
 65 = Predictit market-based probability of the Democrats controlling the Senate. If the Democrats win Iowa and all the states above it, they will have 51 seats, counting the 2 independents as Democrats, and assuming that they lose Alabama. If they win North Carolina and all the states above it but lose Iowa, they will have 50 seats. They will still control the Senate if they win the White House. According to the ranking assumption, the Predictit market probablility that they control the Senate is thus 60 percent (the probablity they win North Carolina) if they win the White House and also 60 percent (the probablility they win Iowa) if they don't. If we use the Predictit market-based probabilty of 65 percent that the Democrats win the presidential electon, then the ranking assumption probability that the Democrats control the Senate is 0.65x60 + 0.35x60, which is 60 percent. This is slightly smaller than the Predictit market-based probability of the Democrats controlling the Senate of 65 percent. So the market is not quite using the ranking asssumption.