Very small changes in the Dem / GOP mix make a YUGE difference.
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A recent WaPo poll had Clinton over Trump by 2 points.
Naturally, voter preference varied by self-proclaimed party affiliation:
Clinton got 86% of of the Dem vote; Trump got 88% of the GOP vote.
Independents went 47% to Trump and 40% to Clinton.
WaPo weighted their sample 37% Dems, 30% GOP and 29% Independents.
In concept that weighting should represent WaPo’s best guess as to the mix of voters on election day.
Some pundits argue that WaPo’s aggregate tally over-weights towards Dems.
Maybe it does, maybe it doesn’t. We’ll know in a couple of days.
For today, let’s just play around with the numbers to demonstrate how critical the turnout assumptions are …
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Let’s start by checking the WaPo calculations…
The WaPo weightings and the voter preferences actually roll up to slightly different numbers than WaPo puts in the headline.
Not a big deal: Clinton 45.2%, Trump 43% … 2.2 points difference.
Why are the numbers different?
Sharp eyes may have noticed that 37% + 30% + 29% doesn’t add up to 100% … it only adds up to 96%.
Again, that’s not a big deal … just means that the numbers need to be massaged a bit.
To make things simple, we’ll compare to these ‘actual’ calculations from this point forward.
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Now, let’s see what relatively small changes in the turnout weightings do to the overall result.
Still using the WaPo voter preferences by party affiliation, we can solve for a turnout mix that puts Clinton and Trump in a dead heat.
Note that it only takes a 1.4% shift in the Dem / GOP weightings to make the race a tie.
Said differently, if Dem turnout is 35.6% (instead of 37%) and GOP turnout is 31.4% (instead of 30%) … then the race is tried.
And, that’s still using the WaPo party-affiliated voter preferences – 86% of Dems for Clinton, 88% of GOP for Trump.
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Let’s do one more scenario ….
Let’s assume – as some pundits do — that an equal number of Democrats, Republicans and Independents show up at the polls.
That is, Dems are 32% of the mix (instead of 37%), GOP are also 32% (up from 30%) and Independents go from 29% to to 32%
Look what happens:
Through the miracle of simple arithmetic, Trump goes from a 2.2% deficit to a 3.5% lead … all while holding the WaPo party-affiliated voter preferences constant.
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So what?
Bottom line: The headline numbers that are being reported shouldn’t be taken too literally … they are way too sensitive to the the polls’ turnout assumptions.
More practically, the conclusion to be drawn is that — since both candidates are preferred by roughly the same percentage of their own-party voters – the election will hinge on relatively small spreads in voter turnout.
It’ll be Clinton’s ground game against Trump’s momentum.
We’ll know in a couple of days.
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