Thursday, August 18, 2016

Presidential Election & Polls: Mid-August Update, Battleground States

In early July I posted a 2012 presidential election analysis, comparing state-level outcomes of the election for the "battleground states" with polling from May-July 15 of that year, and found that polling even that early was an excellent indicator of who would win that state: looking only at PPP polling, they correctly predicted 13 of the 15 states, and by taking an average of just 3 polls from that time period, you could correctly predict all 15 states. This post updates a look at the polls from those same 15 states from a post two weeks ago, which looked at the polls up through Aug 5. At that point Clinton seemed to be in a good position. Now she looks even better.

Looking again at the 2012 presidential election, I broadened the number of states included in the analysis, from the original 15, now to 23. Originally I only looked at states that were won with a 10% margin, now I include states won with a 15% margin. Averaging all polls that only included "likely voters" (and PPP, which uses "registered voters", but is a highly reliable pollster) that were administered from Aug 1-Aug 20*, produced the results in Table 1. Comparing those averages with the actual win margin for either Romney or Obama produced a staggeringly high correlation: r=0.93. Usually social scientists get excited with r>0.5, and ecstatic for r>0.7. What r=0.93 indicates is an incredibly strong reliability between the August polling and the margin of the win. For example, the only poll on record for Montana for early August gave Romney a 17 pt win, and he won by 14%. Similarly, the only poll for Washington gave Obama a 17% win margin, and he won by 15%.

In the current election, various problems have arisen with the Trump campaign--largely because of continued inflammatory statements by Trump himself. While Clinton has some of the lowest "favorability" ratings of presidential nominees, she is still far ahead of Trump in the polls, and she is particularly cutting away at the leads that Trump needs to have in these battleground states. The data from current polls can be found in Table 2, which represent an average of all of the polls from Aug 1-Aug 18 for these states, where polls are available for this time frame. Polls were retrieved from RealClearPolitics and 270ToWin.

At a baseline, Trump needs to win all of the states that Romney won in 2012, plus more, in order to beat Clinton. In the table, I have highlighted in red the states that Romney won, and in blue the states that Obama won. Column 3 is the win margin for either candidate. The last column is the average of all August polls ("likely voters" only). Several states do not have any August polling yet, designated with "NA". In that column, I have highlighted in red those states where Trump leads with more than 5%, and in blue those states where Clinton leads with more than 5%. Green are those states with less than 5% win for either candidate. Recall that the 2012 August polling was highly predictive not only of who would win that state, but of the win margin. So even though the states here highlighted in green are largely within the margin of error, going by the 2012 results, they might still be predictive.

The problem for Trump at this point is that he is under water, and not just by a little bit. He is only winning one of these 23 battleground states by more than 5%, Indiana, based on just one poll. However, for what it's worth, a Democratic internal poll for Indiana actually shows that Clinton and Trump are tied. Clinton is winning seven of these states by by more than 8% according to these polls. Even a state like South Carolina, which has Trump in the lead by 2%, Romney won by more than 10%. Arizona has Clinton with a tiny lead, which Romney won by more than 9%, and he is tied with Clinton in Georgia. In Georgia!

While pundits have got this election wrong for the last year--mainly in predicting that Trump would never get as far as he did--none of those predictions were based on data (unless you count historical wisdom as data). In this case, polling is clearly on the side of Clinton, and at least in the 2012 election, it seems that the voters in these states had already made up their minds as of August, and polling detected it quite accurately. If pollsters are doing a similarly good job this year, and if voters are on the same cognitive-political timeline as in 2012, then Hillary should start measuring for White House drapes, unless the old ones are still in storage.

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