Political polls provide crucial information during elections. When done correctly, small samples can predict the outcomes. We’re approaching election time here in the U.S., and campaigns are switching into high gear along with political polls!
You’d think that conducting a poll is straightforward. You ask a bunch of people who they’ll vote for and count the results, right? But it’s not quite that simple.
For starters, political polls face the same challenges as other polls. However, a poll taken for political reasons also has some unique issues. When pollsters do everything correctly, the small, sampled group accurately reflects the entire population. The trick is to do it correctly!
In this post, learn how statistical concepts apply to political polls and the extra difficulties they face.
Political Polling and Representative Samples
Whether you’re working on a research project or a poll taken for political reasons, you can’t base your sample on convenience. Convenience sampling is a sure way to bias your results because the easy-to-obtain samples are probably different from the harder-to-obtain samples. For political polls, the people closest to you tend to have more similar views. Consequently, pollsters specifically find ways to include those who are not easily accessible in order to represent everyone.
Random samples are the best way to represent a population. In order to obtain a random sample for a political poll, all members of the population must have an equal probability of being selected. Political polling organizations can’t poll people at malls, ballparks, or office buildings because Americans are not equally likely to be at these places.
However, most people have a residence and a phone. Therefore, political polls are generally conducted by calling people at their residence. Pollsters can’t use the phone book because one-third of residential phone numbers are unlisted. And the massive growth of cell phones has changed the polling landscape even more.
So, political pollsters have a complicated process to create their own complete list. The polling organization can then randomly call household phones from their list to obtain a pretty good, but not perfect, random sample.
Even after all of this work, this process still excludes certain portions of the population, including students on campus, personnel on military bases, prisoners, hospital patients, and the homeless. Even for a dedicated, professional organization, it’s hard to get a truly random sample. (Don’t confuse a random sample with a haphazardly collected sample!)
Learn more about Representative Samples and various Sampling Methods in Research.
Identifying the Target Population for Political Polls
Whether you are sampling parts or people, you need to identify the population. For political pollsters, just calling people randomly isn’t good enough. They need to identify their target population. There’s more to this than meets the eye.
For political polls about specific races, you want to target the specific geographic region for that race. National numbers for a local race won’t help you! More specifically, you want to poll people who are not only old enough to vote but are also registered to vote. However, it goes even further than this!
If you want to predict an election, you only want to count registered voters who will actually vote! It really makes a difference. It’s not unusual that the turnout of eligible voters is only 40%. And, there are differences between those who vote and those who don’t. It’s not unusual to see a gap of 3-5 points when you compare eligible voters to likely voter groups in the same poll.
To pick out the likely voters, the political pollsters ask questions about the respondent’s voting history. Each polling organization has its own, highly-guarded method for filtering out the likely voters.
Learn more about using Samples to Estimate Populations and Sample Statistics vs. Population Parameters.
Political Polls and Accurate Measurements
Accurate measurements are important for any study, including a poll taken for political reasons. Each area has its own measurement challenges. For example, quality improvement initiatives need to worry about the standards by which inspectors approve and reject parts.
In political polling, the phrasing and order of questions are hugely important. It’s all too easy to bias the results with poor questions. According to Gallup, describing something as a “welfare program” or a “program for the poor” can change the answer. Should the pollster ask about “sending” or “contributing” troops to a UN program? Which wording yields the responses that truly represents the entire population?
Political pollsters will often test different wordings to assess the impact. Some questions will be asked different ways in the same poll to create a more nuanced understanding. Other questions will always be asked the same way to allow for a comparison over time. Measuring opinions is both an art and a science!
Learn more about Accuracy vs. Precision.
Margin of Error
Like all sample-based statistics, political poll results produce a point estimate and a margin of error/confidence interval. The margin of error assumes that the sample is randomly drawn and it depends on the sample size. A larger sample size will shrink the margin of error.
You can calculate the margin of error using statistical software. Suppose we wanted to calculate the margin of error for a politician with a 50% approval rating based on a sample size of 1,000. Fill out the dialog like this:
We get this output:
This tells us that the margin of error is approximately +/- 3.2%. The politician’s true approval rating is likely to be between 46.8% and 53.2%.
It also easy to calculate the margin of error by hand. To learn more this concept and its calculations, read my post about the Margin of Error.
Lessons Learned
The process required for a poll taken for political reasons is very similar to that of any statistics-based study.
- Don’t underestimate the effort required to get a true random sample. Be sure that all elements the population for your political polls have an equal chance of being selected.
- Accurately target your population. The results from political polls are only reliably representative of the population that the pollsters sample. If you sample the incorrect population, your results may be worthless.
- Accurate measurements are crucial. You can have a perfect random sample from the correct population, but it’s all for naught if your measurements are inaccurate.
- Understand the margin of error or confidence interval. Because you’re sampling a subset of the population, there is bound to be uncertainty. It’s crucial to factor that uncertainty into your assessment of political polls.
Finally, there is no substitute for using your subject area knowledge while conducting an experiment and interpreting the results. This remains true for political polls!
Comments and Questions