There are 35 senate elections (excluding Louisiana) and 36 gubernatorial elections. We had expected vote shares for all of them, in terms of two-party vote share, which were primarily generated from traditional polling.
In 54 of 71 (76%) elections the Republican candidate over-performed (28 of 35, 80%, senate and 26 of 36, 72%, governor). The average error (the bias in one direction) was 2 percentage points (the average absolute error was just 2.8 percentage points). The bias was a little more extreme in the gubernatorial elections (2.3 percentage points), than in the senatorial (1.8 percentage points). Since almost all errors were in the same direction, the absolute error is not much larger than the error.
PredictWise went into Election Day with 27 elections that had a non-negligible probability for both candidates. Of those elections 20 or 74% moved more Republican; the bias was 1.8 percentage points and the average absolute error was 2.2 percentage points. Much of this was driven by Maryland where the error was 9.9 percentage points! The gubernatorial elections had a bias of 1.6 percentage points (1 percentage point without Maryland) and the senatorial elections had a bias of 1.9 percentage points.
The interesting thing is breaking the group up into likely Republican and likely Democratic. In 13 of 14 elections that leaned Republican, the Republican did better than expected. In the remaining 13 elections the Republicans did better than expected in 7 of them. Actually, without Maryland, the Democratic leaning states had no bias, and tiny average absolute error of 1.5 percentage points.
What does this all mean for traditional polling and voting? That is the puzzle that we will explore over the next few weeks and months.