(CNN Student News) -- Use this information to understand how polls are conducted.
"If democracy is supposed to be based on the will of the people, then somebody should go out and find out what that will is."
Dr. George Gallup
In 1936, the Literary Digest predicted that Republican Alf Landon would defeat President Franklin Roosevelt. Dr. George Gallup interviewed a much smaller sample and got it right: Roosevelt by a landslide.
What happened? The Literary Digest surveyed people from its subscription lists, automobile registration lists and the telephone book. During the Great Depression, anyone who owned a car or had a telephone was more likely to be Republican. Gallup selected his sample randomly and managed to get the real pulse of the nation.
It's like asking a class of students if they are in favor of eliminating homework, as opposed to asking random people in a community. The students are unlikely to reflect the views of the community as a whole.
Gallup showed that surveying just 1,000 Americans provides an extremely accurate snapshot of American views, as long as pollsters choose those people randomly.
Today, technology helps pollsters select random samples.
With telephones in almost every home, polling companies use random-digit dialing to create computer-generated lists of phone numbers. Pollsters then call the numbers, not knowing anything about the person on the other end of the line. During the call, interviewers ask demographic questions such as age, education and income levels.
For political polls, people may be asked if they are "likely to vote." On political matters, polling "likely voters" yields better results than just polling everyone. That's why polls are often presented as a percentage of "likely voters."
A poll's margin of error is determined by sample size. According to Gallup Poll company experts, 1,000 Americans can validly indicate the political leanings of the rest of the nation within 3 percentage points, as long as the sample is truly random. In a survey of 2,000 randomly selected people, the margin of error drops only 1 percentage point, making 1,000 the most cost effective sample group, according to Gallup.
(Sources: Encyclopedia Britannica, Gallup) E-mail to a friend