The senatorial forecasts have remained remarkably steady over the last week with two small exceptions. First, Kansas has come into stronger focus and the Independent Orman is pulling away from the incumbent Roberts. Second, Michigan, which was leaning heavily Democratic is now a solid Democratic (and off of our chart!).
I have also updated the forecast for balance of power. For those of you who watch the site closely, you may have seen a small, but reasonable discrete jump when I went live with my updates about 2 AM ET on 10/8/2014. The reason is that I was previously assuming that Orman was 100% likely to caucus with the Democrats. Now, the calculations assume that Orman is 100% to caucus with the Democrats if they get 50 or more seats, 100% to caucus with the Republicans if they get 51 or more seats, and 50% to the caucus with either party of the final tally (excluding him) is 50 Republicans and 49 Democrats. Thus, what I have done is derived the balance of power as if the Kansas race did not exist and then add in the possible effect of the Kansas election. I will update this choice as Orman’s choice comes into focus. Further, the prediction market forecast that is directly forecasting balance of power is a few percentage points different from the aggregated balance of power prediction generated from the state-by-state elections. In order to ensure consistency, the topline balance of power numbers now reflect the aggregated forecast of the states, but all data is noted.
The forecasts from the major news organizations are converging, which is not surprising. More unique fundamental forecasts that dominate early stage forecasting are now completely supplanted by heavy polling, which everyone sees.
Here is New York Times and FiveThirtyEight compared with PredictWise. Not too much difference: