From 2004 to 2012, only thirteen Senate races have had margins of less than three percentage points in the week before the election. Of these, four were won by the trailing candidate. One more, the Florida 2004 race, was tied in the polls, and was eventually won by the Republican, Mel Martinez, by 2 percentage points. Scoring that one as half correct, the overall rate of wins by a front-runner is 65%, a bit better than chance.
In light of that, the probability that all six close Senate races (AK, CO, IA, KS, NH, and NC) will be won by the candidate in the lead is only 7%. A wrong call is almost inevitable. We should not be surprised to see one to three races to be won by the candidate who trails this morning. This allows us to hazard a guess as to the most probable path to Democratic retention of the Senate (which PEC currently has at 35%).
Last night, I gave poll-based probabilities for Senate and governorships. Republicans are favored to take over, but what is the likeliest route to Democrats retaining control? To estimate that, I will use the margin/standard-error-of-the-mean (margin/SEM) ratio (see table at the end of this post) as a measure of which margins are flakiest. From this, upsets seem likely in Iowa (margin/SEM=1.0/0.8=1.3), followed by Alaska (margin/SEM=1.0/1.7=0.6). If they flip, that gives
Democrats+existing Independents: 45 safe seats plus NH, NC, IA, and AK. Total: 49 seats.
Republicans: 45 safe seats plus AR, KY, LA (runoff), GA (maybe runoff). and CO. Total: 50 seats.
Kansas: Orman, who would make the 50th vote for the Democrats+Independents – or facilitate a power-sharing arrangement.
I note that the margin/SEM ratio in New Hampshire is 3.1, suggesting I might escape having to eat a bug.