While presidential candidates George W. Bush and Al Gore will be making plenty of speeches in the coming months, the American public will be talking back in numbersthe numbers of national polls. What can these polls tell us?
According to the Gallup Organization, one of the nation's best known polling groups, Texas Governor George W. Bush is on a roll in the race for president. A Gallup survey of likely voters on July 25 and 26 found that Bush leads his rival, Vice President Al Gore, by a 54% to 40% margin. Less than two weeks earlier, Bush led by only 48% to 46%.
But not so fast! Political
experts point to a Bush "bounce" leading
up to last week's Republican convention
in Philadelphia, Pennsylvania. A similar
bounce may benefit candidate Gore later
this month when the Democrats convene
in Los Angeles, California. The lesson
here is that a candidate's popularity
in the polls may vary greatly from week
Below, you can get a longer view of how Bush and Gore have fared in Gallup polls:
Based on the data above, what has been the smallest percentage difference between the candidates? What has been the largest percentage difference?
Estimate what Bush's average lead has been since February.
How many times has Gore led the Gallup presidential poll since February?
Many organizations poll the voters, from news outlets to public interest groups to the candidates themselves. Their hope is to predict accurately how the entire population will vote, based on interviews with only a small percentage of that population. According to Gallup, which has been in the polling business for much of the last century, a poll of any kind is only as good as the sample selected to interview.
The key, says Gallup, "is a fundamental principle called equal probability of selection, which states that if every member of a population has an equal probability of being selected in a sample, then the sample will be representative of the population."
How accurately has Gallup predicted the outcome of recent elections? In 1996, the final Gallup poll predicted a 52% victory for President Bill Clinton. Clinton actually won 49.2% of the vote. In 1992, Gallup predicted 49% of the vote for Clinton, but he received just 43%. That was enough for victory in a three-candidate race.
Getting a Good Sample
The Gallup Organization has gone to considerable lengths to get a fully random sampling of the people they are polling. From the 1930s to 1980s, Gallup representatives went door-to-door to homes in every state in the country.
Gallup began using the telephone to reach the public. Gallup researchers developed a computerized process that generates a list of all the possible phone numbers in the United States (including those that are unlisted). The computer then randomly selects a group of numbers to call.