Snapshot probability distribution of all possible outcomes calculated from current state polls. The blue bars represent combinations of outcomes leading to Democratic control. The red bars represent Republican control. The green bar indicates outcomes in which Democrats and Independents control 50 votes, and independent Greg Orman of Kansas provides one of the votes. In this case Orman’s choice of caucus will determine control of the chamber. This a snapshot, based on conditions today, of the polled demographic. It does not take into account the possibility of midterm polling bias, which adds uncertainty of +/- 2.5%.
Because the green bar is ambiguous, human factors come into play. The histogram above, which is based purely on polling data, allows you to play out your own scenario regarding those human factors.
This distribution includes pollster-to-pollster “house effects” as part of the variation. On Election Eve its center should be close to or at the final election outcome.