Grover's Take on Things

This is Part 3 of a weekly series I am doing, tracking the 2014 political predictions of polling guru Nate Silver. (This is a stand-alone essay, but it’s possible you may wish to look at Part 1 and Part 2.) Here are the most important, and in some cases quite surprising, bullet points in his predictions as of today; details and expanded information are in the sections below.

• National Senate Predictions.  Silver predicts there is a 60.7% chance that Republicans will win a majority in the U.S. Senate. The New York Times and The Washington Post both predict the same outcome, but with larger percentages.
• North Carolina.  Silver predicts a 71% chance of Kay Hagan (D) defeating Thom Tillis (R). Currently he predicts a 48.1%-46.2% margin, the gap having shrunk to +1.9 percentage points. Two major polling and analysis organizations, Real Clear Politics and Rasmussen, have moved the race to the level of “toss-up.”
• The Maroon 6.  Silver has moved Georgia from a close Republican win to an exact tie in the vote between Michelle Nunn (D) and David Perdue (R), 47.7% to 47.7%. He nevertheless lists a 51% chance that Nunn will win. (According to Silver’s Maroon 6 theory, this could significantly lessen the Republican’s probability of winning the Senate. See below for the theory behind the Maroon 6.) The New York Times also now predicts this race is a percentage point tie.

(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.)

National Senate Predictions.  As seen in the “How It’s Changed” graph, Silver’s projection has contracted slightly this week for the GOP, predicting the probability of Republicans controlling the Senate now at 60.7%, down slightly from last week’s 62.2%.

Analysis and Graph by Nate Silver (24 Oct 2014)

Senator Kay Hagan and Speaker Thom Tillis

North Carolina.  For the NC Senate race, Silver’s prediction of a Kay Hagan (D) win over Thom Tillis (R) has fallen to 71%, down from last week’s 76%. This is coupled with a much reduced predicted margin of victory, down to 1.9 percentage points, 48.1% to 46.2%. Two other major polling and analysis organizations have moved this race to the level of “toss-up.” (See “Other Predictions” section, below.)

(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%.)

The Maroon 6.  Somehow, Silver is predicting that Georgia’s Senate race is exactly tied, 47.7% to 47.7%, but he has predicted a 51% probability that Michelle Nunn (D) will win. (I’m not sure how this math works, unless he is factoring in some sort of “trending” factor.) This prediction potentially has huge implications for Silver’s “Maroon 6” construct. He has identified six states that he calls the “Maroon 6,” with Senate races 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%. Given his current prediction of the Democrats’ taking Georgia, this theory automatically depresses the “Maroon 6 Prediction” of Republicans’ taking the Senate to 84%. Should Georgia and any other of the 6 states go to the Democrats, Republicans’ chances to control the Senate drop precipitously, to levels that strongly predict Democrats’ keeping the Senate. The table shows Silver’s current “Maroon 6” state predictions.

Other Predictions:

• The New York Times‘ online TheUpshot page currently predicts: “According to our statistical election-forecasting machine, the Republicans have a moderate edge, with about a 67% chance of gaining a majority.” They predict an 79% likelihood that Kay Hagan (D) will defeat Thom Tillis (R), and that the margin will be +2.4 percentage points. [These are down slightly from last week, when Hagan was 81% likely to win by a predicted 2.9 percentage points.]
• The Washington Post’s Election Lab states: “Republicans are favored to control the Senate. 91% chance as of today.” [This is down slightly from last week’s predicted 96% chance of a Republican win.] They continue to give Kay Hagan (D) a 95% chance of keeping her seat.
• When forced to make best current predictions for all Senate races (including those they now call “toss-ups,” Real Clear Politics predicts a 6-seat net pickup by the Republicans, giving them a 53-47 majority. [This is down from their last week prediction of an 8-seat majority for the GOP.] They list the NC Senate race a “toss-up,” showing Kay Hagan’s (D) current margin over Thom Tillis (R) a mere +1.6 percentage points, up very slightly from last week’s 1.4 percentage point prediction.
• There is no difference this week in the predictions by Rasmussen Results. They label the NC Senate race a “toss-up.” In their most recent poll (taken Oct. 6-7), Hagan (D) polled at 48% and Tillis (R) polls at 46%. The margin of error in that poll of likely voters was +/-3 points, placing these results within that range.

That’s all until next Friday.