Justin Meyer dismantles the bad math behind the media’s new ‘the wave is fading’ narrative

My science professor friend, Justin Meyer, is back at it (see our earlier blog post on Oct. 3rd). He, like me, follows political news and enjoys dispelling gibberish. He sniffs out mathematical mischief the way a German Shepherd sniffs out a jittery perp. He has a nose, in particular, for  problems with the interpretation of political numbers. Here’s his description of why the news of a narrowed enthusiasm gap between Republicans and Democrats may not mean what you think it does. (In typical scientist fashion, he makes it short and sweet.)

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Recently, it was reported by NBC and other news outlets that the enthusiasm gap is narrowing between Republicans and Democrats. Everyone is well aware of the predicted ‘blue wave.’ Do the numbers behind this new reporting really suggest there won’t be a wave? No one can know for sure whether the wave will materialize, but the statistics, somewhat counterintuitively, foretells a sizeable wave.

A recent NBC/WSJ poll revealed that Democrats are still more enthusiastic than Republicans, but not by much. 72% of Democrats are enthusiastic to vote, while 68% of Republicans are. Even though this margin seems slim, it does not mean that there will be a close election. This is because there are more Democrats than Republicans. If the larger political party has more enthusiasm, even slightly more enthusiasm, then there’s no hope for the smaller party.

Let’s walk through what this 4-point gap means for the election.

If we assume that Independents don’t vote and that all voters are faithful to their registered parties, then the Democrats would win by 16 percentage points nationally.

How was this calculated? A 2017 Gallup poll reported that 31% of registered voters are Democrats, while 24% were Republican. In 2016, the US reached a new high level of registered voters, 200 million. If we assume that the number of voters hasn’t increased and that all the self-reported enthusiastic voters vote, then by taking the size of the electorate (200 million) and multiplying by the fraction of registered voters who are Democrats (0.31) and then multiplying by the proportion that is enthusiastic (0.72), the number of Democratic votes is ~45 million. The same calculation for the Republicans yields ~33 million. These numbers translated into percentages show a huge national victory for the Democrats; ~58% to ~42%.

The problem with the 4-point gap figure is that the percentages being compared (72 verses 68) are of two different populations (Democrats and Republicans) and so the calculation is meaningless. If you did this on a math exam, your professor would rightfully fail you.

The take-home message is to be careful when interpreting polling data. And, bottom line, don’t let poll numbers affect your mood or shape your enthusiasm. Democrats, keep volunteering and make sure to vote. Bring your predicted win across the finish line.

 

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