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Predicting the President

Can math pick the winner of the election?

Voters will cast their ballots for the next president of the United States on Tuesday, November 8. But before the votes are counted, people want to know: Which candidate has the best shot? 

To answer that question, we turn to pollsters. These political pros interview voters to learn which candidates they support and what issues they care about. Pollsters then use that data—and math—to make informed guesses about which box voters will check on election day.

With more than 146 million registered voters in the U.S., pollsters can’t speak to every single one. Instead they talk to a small group, called a sample. “The trick is that the sample has to represent the much bigger number of people who vote,” says J. Ann Selzer. She’s the president of Selzer & Co., her polling company in West Des Moines, Iowa.

After interviewing the sample, pollsters sit down to do some math. “The most important quality in a pollster is a math-centered mind,” says Selzer. “We do division daily! We take the number of people who gave a certain answer and divide it by the total number we talked to.” That data is used to calculate a percentage. 

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These percentages allow pollsters to make comparisons between groups—such as men and women, or older and younger voters—and to say that certain groups are more likely to vote a certain way.

Polls aren’t always 100 percent correct, though—and sometimes they’re totally wrong. The most famous misstep happened in 1948. Pollsters predicted that Thomas E. Dewey would win the presidency over Harry S. Truman. The Chicago Daily Tribune even printed a story declaring Dewey’s victory. Imagine everyone’s surprise when Truman won! 

Polls can be misleading for many reasons. For example, questions with confusing wording can skew results. And if the sample of respondents isn’t diverse enough, the poll won’t correctly reflect the opinions of all voters. But pollsters try to minimize these errors.

Reliable polls serve an important function in democracy: They help politicians understand what voters are thinking, and they show which candidates are in the lead. Most important, “polls are a way for the voice of the people to be heard,” says Julia Clark, a senior vice president at the polling company Ipsos. “That’s good for politics and good for everyone.” 

Calculate percents based on the results of a political poll, using the data shown in the table below.

A. What percent of respondents ages 18-29 said they would vote for Hillary Clinton for president?

B. What percent of that age group said they would vote for Donald Trump for president?

Among voters who support Trump, which age group represents the highest percentage? What was that percentage?

Among voters ages 30-59 combined, which candidate (or option) was chosen by the highest percentage of voters? What was that percentage?

According to this poll, what is the difference between the percent of respondents of all ages who would vote for Clinton and those who would vote for Trump?   

Do you think that the results of this poll accurately reflect what is likely to happen in November? Why or why not?

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