Grover's Take on Things

This is Part 4 of a weekly series of reports I am doing, tracking the 2014 political predictions of polling guru Nate Silver prior to Election Day. I will have a “How Did He Do?” report next week to close out this series. (This is a stand-alone essay, but it’s possible you may wish to look at Part 1, Part 2, and Part 3.) Below are the most important bullet points in his predictions as of today.

Analysis and Graph by Nate Silver (31 Oct 2014)

• National Senate Predictions.  Silver’s prediction concerning control of Congress’ upper chamber has moved to its highest probability level since he started assigning them: a 68.9% chance that Republicans will win a majority in the U.S. Senate. This equals The New York Times‘s 68% probability of a GOP takeover.
• 

  Senator Kay Hagan and Speaker Thom Tillis

  North Carolina.  The NC Senate race, according to Silver, continues to tighten. As opposed to the 3-percentage-point margin he predicted 4 weeks ago, he has now shrunk Kay Hagan’s (D) margin over Thom Tillis (R) to 1.3 percentage points. He sees a 67% chance of a Hagan (D) win, which is down considerably from his 79% probability 4 weeks ago. The New York Times, Real Clear Politics, and Rasmussen are all leaning toward Hagan (D), and all currently see the gap at a whisker-thin 1 percentage point.
• The Maroon 6.  Silver has switched his prediction in Georgia back to a win by David Perdue (R) over Michelle Nunn (D). This has significant ramifications for Silver’s “Maroon 6” concept. (See below.)The New York Times also now predicts this race is a 0.6 percentage point dead-heat, with a 57% chance of a Perdue (R) victory.

(Why keep an eye on Nate Silver? He’s the young probability/statistics guru who, unlike all of his peers in the business, correctly predicted the results of the 2008 Presidential race in 49 of 50 states, and the results of the 2012 Presidential race in all 50 states.)

In his construct of the Maroon 6. Silver has identified six states with Senate races he says are key to watch: Alaska, Arkansas, Georgia, Iowa, Kentucky, and Louisiana. His calculations tell him that if Republicans win all 6, they have a 99% chance to take the Senate. If they win 5, their chance slips slightly to 84%. With anything less than 5 wins, however, Republicans’ chances to control the Senate drop precipitously, to levels that strongly predict Democrats’ keeping the Senate. Right now, on his state-by-state predictions, he is showing Republicans ahead in all 6 — though the races in Iowa and Georgia are currently extremely close.

(Please note that when I use the shorthand “Silver predicts victory…,” I am saying that, in that race, his percentage probability of victory for that candidate currently sits at greater than 50%.)

Other Predictions:

• The New York Times‘ online page TheUpshot page currently predicts: “According to our statistical election-forecasting machine, the Republicans have a moderate edge, with about a 69% chance of gaining a majority.” They predict an 68% likelihood that Kay Hagan (D) will defeat Thom Tillis (R), and they predict that the margin will be +1.1 percentage points for her. [These are down appreciably from last week, when Hagan was 79% likely to win by a predicted 2.4 percentage points.]
• The Washington Post’s Election Lab states: “Republicans are favored to control the Senate. 95% chance as of today.” Currently they predict the GOP will begin 2015 with 52 seats in the Senate. In North Carolina, the Post gives Kay Hagan (D) a 77% chance of keeping her seat, which is appreciably smaller than their 95% prediction last week.
• When forced to make best current predictions for all Senate races (including those they now call “toss-ups”) Real Clear Politics predicts a 7-seat net pickup by the Republicans, giving them a 52-48 majority. RCP’s average of polls currently predicts the following for North Carolina: Hagan (D) 44.1%, Tillis (R) 43%, and Haugh (L) 4.7%
• Rasmussen Results is now showing Hagan (D) 47% over Tillis (R) 46% in their most recent polling. Hagan (D), therefore, has lost a percentage point since their previous poll, where the gap was 48% to 46%.
  
  That’s all until after the election.