Of the 37 Senate seats contested in the November 2, 2010 elections, 36 were resolved by November 4, including very close outcomes in several states. Of these 36, the FiveThirtyEight model had correctly predicted the winner in 34. One of the two misses was in Colorado, in which the incumbent Michael Bennet (D) outpolled the challenger Ken Buck (R) by less than 1 percentage point. The 538 model had forecast that Buck would win by 1 percentage point. The second miss was in Nevada, in which the incumbent Harry Reid beat challenger Sharron Angle by 5.5 percentage points, whereas the 538 model had forecast Angle to win by 3.0 percentage points. Silver has speculated the error was due at least in part to the fact that polling organizations underrepresented Hispanic voters by not interviewing in Spanish.[95]
In the remaining contest for U.S. Senate, in Alaska, the electoral outcome was not yet determined as of November 4, pending a count of the write-in ballots, but in the end the FiveThirtyEight forecast of GOP nominee Joe Miller as winner ultimately proved to be wrong, as write-in candidate, incumbent Republican Senator Lisa Murkowski, prevailed.
The 538 model had forecast a net pickup of 7 seats by the Republicans in the Senate, but the outcome was a pickup of 6 seats.