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Pennsylvania’s Delegate Rule: Tempest in a Teapot?

April 24th, 2016, 12:00pm by Sam Wang

I am chuffed about the initial match between Indiana polls (Trump +7%) and a “demographics-less” prediction based on border counties (also Trump +7%). A second demographics-less method, based on Google Correlate, also performs very well. In the coming weeks, we will see how these two approaches do.

I have provided predictions separate from polls. I find it confusing to mix up a secret-saucey prediction with hard polling numbers. Unlike other sites’ evaluations [NYT] [538], the approaches presented here are transparent. It is easy to do the predictive calculations yourself, and I hope you will try them out yourself!


As I pointed out in March, Kasich’s win in Ohio was good for Trump because it kept the anti-Trump opposition divided. In Pennsylvania, Donald Trump is polling at a median of 42% (n=4 polls, April 7-18), with a divided opposition (Ted Cruz at 26%, John Kasich at 23.5%). There is little doubt about who will win the popular vote there on Tuesday.

In the overall PEC calculation of expected GOP delegates, Trump should receive all 71 of Pennsylvania’s delegates based on voting. I’ve written about this calculation and assumption before. Today, to expand upon those thoughts…

Despite the lack of suspense, horserace commentators are attempting to inject uncertainty by going off about the delegate-selection rule in Pennsylvania, which lists delegates on the ballot without a candidate’s name listed. As the argument goes, Trump could be deprived of 54 district-level delegates (3 in each of the 18 Congressional districts).

I say: meh.

The problem with the argument is that the Republican National Committee has made it clear that delegates should commit on the first ballot to a statewide or district-level winner. Pennsylvania Republicans may have nominal freedom, but they know perfectly well that they should vote for their district’s winner. Since district-by-district standard deviation of vote share is typically around 5%, Trump’s 16-percentage-point lead will probably translate to winning all 18 districts, a clean sweep.

Support for the idea of delegate fidelity comes from the Tribune-Review, where Tom Fontaine and Salena Zito contacted Pennsylvania’s 162 delegate candidates, and 110 responded to their survey. The results suggest that the majority feel pressure to comply with voter wishes:

Only 21 respondents – 19% of the total – explicitly said they would vote for someone other than Trump. Let’s say that the 54 winning delegates are representative of this group. It seems to me that there would be fewer Cruz-supporting delegates if their preferences become known to voters by Tuesday. But let us imagine that Cruz picks up 19% of district-level delegates, 10 in all.

The PEC overall delegate calculation counts all Pennsylvania delegates as being committed. It currently puts Trump at a median of 1285 delegates; the probability of getting at least 1237 delegates for a majority is 75%. Under such uncertain conditions (I regard probabilities of 20-80% as uncertain), losing 1 delegate would reduce the probability by approximately 0.5%*. So if ten Pennsylvania delegates are faithless, then the probability of Trump getting a majority drops to 70%.

Of course, there are unpredictable multiplier effects here. If Trump does poorly enough that he drops below 1237 delegates, any indecisive delegates may feel at liberty to vote against Trump. And if Trump stays above 1237 delegates without Pennsylvania, Pennsylvania delegates may decide to abandon any thoughts of straying.

Anyway, from a modeling standpoint, considering delegate attitudes, a simple approach that comes fairly close to reality is to assume that Pennsylvania delegates will go with their voters’ wishes. From that, the reader can apply a correction based on human factors. So that’s what I am doing. I leave it to readers to work out for themselves what they think will happen in alternative scenarios.

Update, April 25th: I am starting to lean toward using the Tribune-Review survey to add a “faithlessness factor” in which the number of district-level delegates in Pennsylvania would be multiplied by 0.8. The difference is small, but it would actually capture the probable loss of about 10 delegates. It would also minimize the discrepancy between the model and the eventual outcome.

*This is true for now. if Trump’s expected number of delegates gets farther above 1237, the race will become more certain and the effect of losing a delegate will become much smaller. And of course the converse is true: if he falls short, the race again becomes more certain in the other direction – and the effect of losing a single delegate again becomes smaller.

Tags: 2016 Election · President

4 Comments so far ↓

  • 538 Refugee

    ” chuffed ” ? I’m starting to think you have a ‘word of the day calendar. ;)

  • Amitabh Lath

    Yes, the PA delegate issue, the mystery of unpolled Indiana, does Trump lead broadly enough in CA… all of these are desperate creations of a media being denied a horserace narrative.

    I hope the google correlate idea works out. While the agreement with your border-counties method, and then polls when they appeared is really great, it probably needs some validation before being accepted as a standalone prediction tool.

    • Sam Wang

      Agree, the method could use some error analysis.

      Tempted to implement a faithlessness factor in PA, just to get a stable estimate. It would be about 0.8.

    • AySz88

      For the Google Correlate technique, I would suggest splitting the known votes into two sets (either by calendar, or randomly, and not necessarily equal in size), and seeing how well the technique matches the test set given only the training set.

      I would volunteer, but I have to admit that I’m falling way behind in my ‘neat stuff to try coding’ queue.

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