How does polls work?

JOSEPH LEWIS / ELECTION 2020: 

Hello!  The news is jam-packed with polls.  But how accurate are they?  How much faith should we as voters put in polls, particularly political polls that attempt to predict the outcome of an election?

Political poll is a type of public opinion polling. When done right, polls can be accurate with strict rules about sample size, random selection of participants and margins of error.

How do polls work?  A polling company determines a pool of phone numbers from across the country. Interviewers sit down at computers that begin calling numbers at random. The number of people called varies, but generally it is between 600 and 1,000.  Once an interviewer connects with a respondent, the responses from the call are logged into a database. Those responses are tracked to ensure that the people who are answering the questions represent the region being polled. 

A poll’s margin of error depends largely on the number of people you talk to. If you talk to 100 people for a national poll, you’re looking at a nine-percentage-point margin of error. Crank it up to 600, and you’re down to a four-percentage-point margin of error. As you add respondents, the reduction on margin of error diminishes.

Even the best public opinion poll is only a snapshot of public opinion at the particular moment in time, not an eternal truth.  Voter opinion shifts dramatically from week to week, even day to day, as candidates battle it out on the campaign field.

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Polling has had a bumpy few years after polls in several states overestimated Hillary Clinton’s support in 2016, which led observers to think she was a heavy favorite to be elected president that year, but she lost.  This is unfortunate, largely because polling is broadly trustworthy and informative.

That’s all for now.   I will see you next time.

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