Perhaps the only bigger loser than Hillary Clinton in yesterday’s election was the polling industry itself. Those of us who conduct surveys for a living should be asking if we can’t even get something as simple as a Presidential election right, why should our clients have confidence in any data we provide?
First, a recap of how poorly the polls and pundits performed:
- FiveThirtyEight’s model had Clinton’s likelihood of winning at 72%.
- Betfair (a prediction market) had Clinton trading at an 83% chance of winning.
- A quick scan of Real Clear Politics on Monday night showed 25 final national polls. 22 of these 25 polls had Clinton as the winner, and the most reputable ones almost all had her winning the popular vote by 3 to 5 points. (It should be noted that Clinton seems likely to win the popular vote.)
There will be claims that FiveThirtyEight “didn’t say her chances were 100%” or that Betfair had Trump with a “17% chance of winning.” Their predictions were never to be construed to be certain. No prediction is ever 100% certain, but this is a case where almost all forecasters got it wrong. That is pretty close to the definition of a bias – something systematic that affected all predictions must have happened.
The polls will claim that the outcome was in the margin of error. But, to claim a “margin of error” defense is statistically suspect, as margins of error only apply to random or probability samples and none of these polls can claim to have a random sample. FiveThirtyEight also had Clinton with 302 electoral votes, way beyond any reasonable error rate.
Regardless, the end result is going to end up barely within the margin of error of most of these polls erroneously use anyway. That is not a free pass for the pollsters at all. All it means is rather than their estimate being accurate 95% of the time, it was predicted to be accurate a little bit less: between 80% and 90% of the time for most of these polls by my calculations.
Lightning can strike for sure. But this is a case of it hitting the same tree numerous times.
So, what happened? I am sure this will be the subject of many post mortems by the media and conferences from the research industry itself, but let me provide an initial perspective.
First, it seems that it had anything to do with the questions themselves. In reality, most pollsters use very similar questions to gather voter preferences and many of these questions have been in use for a long time. Asking whom you will vote for is pretty simple. The question itself seems to be an unlikely culprit.
I think the mistakes the pollster’s made come down to some fairly basic things.
- Non-response bias. This has to be a major reason why the polls were wrong. In short, non-response bias means that the sample of people who took the time to answer the poll did not adequately represent the people who actually voted. Clearly this must have occurred. There are many reasons this could happen. Poor response rates is likely a key one, but poor selection of sampling frames, researchers getting too aggressive with weighting and balancing, and simply not being able to reach some key types of voters well all play into it.
- Social desirability bias. This tends to be more present in telephone and in-person polls that involve an interviewer but it happens in online polls as well. This is when the respondent tells you what you want to hear or what he or she thinks is socially acceptable. A good example of this is if you conduct a telephone poll and an online poll at the same time, more people will say they believe in God in the telephone poll. People tend to answer how they think they are supposed to, especially when responding to an interviewer. In this case, let’s take the response bias away. Suppose pollsters reached every single voter who actually showed up in a poll. If we presume “Trump” was a socially unacceptable answer in the poll, he would do better in the actual election than in the poll. There is evidence this could have happened, as polls with live interviewers had a wider Clinton to Trump gap than those that were self-administered.
- Third parties. It looks like Gary Johnson’s support is going to end up being about half of what the pollster’s predicted. If this erosion benefited Trump, it could very well have made a difference. Those that switched their vote from Johnson in the last few weeks might have been more likely to switch to Trump than Clinton.
- Herding. This season had more polls than ever before and they often had widely divergent results. But, if you look closely you will see that as the election neared, polling results started to converge. The reason could be that if a pollster had a poll that looked like an outlier, they probably took a closer look at it, toyed with how the sample was weighted, or decided to bury the poll altogether. It is possible that there were some accurate polls out there that declared a Trump victory, but the pollster’s didn’t release them.
I’d also submit that the reasons for the polling failure are likely not completely specific to the US and this election. We can’t forget that pollsters also missed the recent Brexit vote, the Mexican Presidency, and David Cameron’s original election in the UK.
So, what should the pollsters do? Well, they owe it to the industry to convene, share data, and attempt to figure it out. That will certainly be done via the trade organizations pollsters belong to, but I have been to a few of these events and they devolve pretty quickly into posturing, defensiveness, and salesmanship. Academics will take a look, but they move so slowly that the implications they draw will likely be outdated by the time they are published. This doesn’t seem to be an industry that is poised to fix itself.
At minimum, I’d like to see the polling organizations re-contact all respondents from their final polls. That would shed a lot of light on any issues relating to social desirability or other subtle biases.
This is not the first time pollsters have gotten it wrong. President Hillary Clinton will be remembered in history along with President Thomas Dewey and President Alf Landon. But, this time seems different. There is so much information out there that seeing the signal to the noise is just plain difficult – and there are lessons in that for Big Data analyses and research departments everywhere.
We are left with an election result that half the country is ecstatic about and half is worried about. However, everyone in the research industry should be deeply concerned. I am hopeful that this will cause more market research clients to ask questions about data quality, potential errors and biases, and that they will value quality more. Those conversations will go a long way to putting a great industry back on the right path.