March 26, 2017

Trump Isn’t Losing; The Polls are Just Biased

In recent weeks people have been debating whether or not presidential match up polls are biased in terms of the proportion of their samples which identifies as democrats, republicans, and independents. This article shows that the polls are in fact biased, that correcting for this bias cuts Clinton’s lead over Trump in half, and that looking at likely voter polling, as opposed to registered voter polling, or correcting for general pro democrat bias in polls, suggests that the race is currently too way too close to call and will come down to turnout.

The Polls are Biased Against Trump

Determining whether or not polls are biased is fairly simple. All you need to do is compare the party ID proportions of the general population, or recent voters in presidential elections, to the party ID proportions of match-up polls.

I did this with 5 recent polls by Reuters/Ipsos, Fox, Yougov, Quinnipiac, and Morning Consult. Comparing their party ID proportions to Party ID polls done by Pew and Gallup, as well as 2012 presidential NYT exit poll party ID proportions, it was clear that recent polls over sample democrats and under-sample republicans and independents.

The Reuters poll, which had Clinton winning by 10 points, is the most extreme example of this.

Bias Chart 1

These 5 recent polls had Clinton winning by an average of 5.6 points. Re-weighting their samples based on 2012 voter turnout shrank that lead to 2.72 points, a reduction of more than 50%.

Correction Chart

The Polls are Usually Biased Against Republicans

Moreover, polls are generally biased in favor of democrats, especially this far out from the election. Specifically, according to an analysis of American polling in every presidential election between 1952 and 2012 polling done around this time period normally over-predicts democrat performance by about 2 points.

Pro Democrat Bias.PNG

Wang (2016)

Now, this might be because polls at this time always have a party ID bias that goes away later on, but I doubt it. There is no reason to think pollsters magically get better at sampling as we get closer to elections.

If this is right, then we can reasonably predict that Clinton will do about 2 points worse than polls are currently saying she will which, after correcting for party ID bias, implies she would win by 0.7 points. In other words, we might reasonably say that the polls are way to close too call and the election will come down to turnout.

It’s worth mentioning that not all poll exhibit anti republican bias. Specifically,  an analysis of American presidential polls from the years 1992 to 2012 found that the median registered voter poll was biased in favor of democrats (by 2 points) but the median likely voter poll exhibited no bias at all.

Likely vs Reg polls.PNG

Silver (2014)

Currently, the only major pollster doing likely voter polls on a regular basis is Rasmussen. Likely voter polls in general have a history of no bias, but Rasmussen in particular over-predicted Romney’s performance in 2012 by 3.7 points. So, with that being said, Trump is ahead by 4 points in the most recent Rasmussen poll. Thus, if we adjusted for their 2012 pro republican bias, we might reasonable say, once again, that the polls are way to close to call and the election will come down to turnout

 

Facebook Comments
  • Alex Andrés

    FIRST!

  • Alex Andrés

    pretty sure this is the only time i’ve ever gotten first comment.

    • Erwin Rommeow

      White privilege strikes again!

  • The Last American

    Looking a swing state polls is also encouraging. Thanks for the analysis

  • Anthony Thomas

    This makes no sense at all. Stop trying to ‘unskew’ the polls. Hillary is still winning either way, so I don’t see your point

    • John J. Barrister

      The issue, from what I gather is when you “unskew” the polls fall within the margin of error and the polls cannot clearly predict the result.

      • Anthony Thomas

        The thing is though, is that polls are not really supposed to predict results. Polls are there to give a range of what the candidate could get. Trying to make the polls all fall in margin of error misses the entire point and is just trying to make every election a toss-up

  • Mengerian Knight

    Hopefully the ((media)) lying will come back to bite them, with Leftists not showing up as they believe the outcome a forgone conclusion.

  • FLOYDINFLORIDA

    Who do they poll certainly not me!
    I like most of you will not answer my cell phone if it is out of area or I don’t know you!
    Just who are they polling and how?
    Every year they poll south Florida and yet West Florida is Extremely Conservative!
    Yep and if I’m a Pollster I can word the poll to make you vote the way I want you too?