Ok, it is time to talk polls. For the second Presidential election in a row, the lack of accuracy from major polling services has been an issue. Before the election, there was skepticism expressed by many, since the predictions of a blue wave as detected by the polls did not match the gut feelings of people on the ground, especially in those states declared to be battleground states. It is always difficult to determine the slope of a line with less than three data points, but in this case, since presidential polling only gets tested every four years, it is appropriate to declare a trend and try to understand why it is occurring. In this regard, I have no knowledge about the internals that polling firms have seen. I am only looking at trends in society in general, and extrapolating them to the polling results.
First, polls are very valuable in estimating the characteristics of a large population, if three criteria are met. Those criteria are:
- Those polled are a representative sample of the population
- Those who respond to polls are honest in their answers
- The technology used to reach those who are sampled matches the technology used by those who are sampled.
The first and third criteria are closely interrelated. Since most polling still depends upon land line responses, the audience for polling is becoming further and further divorced from the population as a whole. That is because fewer and fewer people use a land line, but instead are totally dependent upon their cell phones. If you look over the past decade, the growth of cell phone penetration has been explosive. And another factor that comes into play is that many people automatically disregard phone calls from an unknown number. So if you attempt to contact people on cell phones, you are likely to be ignored by an increasing percentage of the population. Finally, once you have answered the phone, you have the opportunity to opt in to being polled. I normally will opt in unless I am in the midst of doing something else and can’t split my attention. But I would be interested to see if there is a difference in behavior between those who lean left and those who lean right in terms of voluntary opt in percentages. Since so many of those on the right politically now distrust the government and the established elites, my sense is that more people on the right will decline to participate in a survey.
The second criteria, being honest in their answers, is the most subtle factor in determining whether a poll is accurate. Sometimes folks just want to throw a monkey wrench into the works, and so they will deliberately answer inaccurately in order to influence the results. The number who choose this option may be small, but when you are trying to assess a smaller population (like a state), the smaller sample size means each response is proportionally more important. So it can appeal to those who feel powerless in society to try to exert more influence on polls than normal by screwing with the results. For this to affect polling accuracy, it would mean that more people on one side of the electoral continuum would use this than those on the other side. Sounds like a good project for a social scientist to take on over the upcoming years.
Why has polling been so heavily used over the past few decades? Because it worked. When the US was a more homogenous nation, and we all shared a common communications technology (the telephone), it was possible to ensure that you could select a random slice of the population. Call someone up, have them answer a few questions regarding age, sex, and race, and you could slot them into one of the acceptable demographic categories for a poll. In case you haven’t noticed, we no longer fit neatly into categories as we used to. And the longer we go with alternative communications technologies, the further we stray from the easy-to-sample population we had from the 50’s through the 90’s.
Now, as to how the polls are used, you have to stray into the world of mathematics. One of the most common terms you hear is “Margin of Error”. That phrase is bandied about by the Steve Kornacki’s of the cable world along with many others of the pundit class. The formula for margin of error is this:
The margin of error in a sample = 1 divided by the square root of the number of people in the sample
This is what is amazing to understand. It doesn’t matter what is the size of the population being sampled, it only matters what is the size of the sample. That is why having a representative, but random sample of the population is so important. Incidentally, for a +3% margin of error, the sample size would need to be 1090. For a +5% margin of error, the sample size would need to be 400. Usually national samples are larger in order to ascertain valid statistics for subgroups (male, female, white, black, age groupings). But if just the top result is desired with a +3% margin of error, it is possible to sample the entire population of the US with a sample size of slightly over 1000 individuals. This is the magic of polling.
When someone speaks about the margin of error being +3%, what that means is that you would expect the true value for the population to be equal to the sampled value, +3% for 95% of the time. The 95% is a standard confidence limit in statistics, used often to determine if an effect is real or may be just a chance result. So if someone shows a poll support of 45% with a margin of error of +3%, then we would expect the real value to be within 42% to 48% for 95% of the time. If two candidates are being sampled, you look to see if there is any overlap between the 95% confidence intervals for the two. In this case, if candidate A had 45%, and candidate B had 49%, there would be some overlap between the 95% confidence intervals for the two. The range from 46% to 48% would fit both of these candidates. Now, if there is only slight overlap between the two, it is more likely that the one who samples higher is truly ahead, but it is not outside of the standard of 95%.
The 95% confidence interval is used many times in science. It is used in testing of drugs and medical treatments. I used it in production trials in a chemical plant, when we were attempting to determine whether one set of conditions was better than another. Once you are familiar with the math behind sampling, you can use that math in many different ways.
But once again, it all depends upon whether the population that responds to a survey is truly a representative sample of the population as a whole. It seems obvious that at least in the US, there is something wrong with the methodology used to select a random, representative sample. It remains to be seen whether these problems can be diagnosed and fixed before the next huge use of polling coming up in 2024.