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If you choose to follow any links to the abstract and/or complete text of the item listed below, you will be leaving the Strategian Web site. If you wish to return to this page from the Web page you are sent to, please use the Back option of your browser. Andrew Gelman How can a Poll of only 1,004 Americans Represent 260 Million People with only a 3 percent Margin of Error? (... A "3 percent margin of error" means that there is a 95 percent chance that ... you would expect to see a less than 3 percent difference between the proportion of people who say "yes" to the survey question and the proportion of people in the population who would say "yes" if asked. How is it that a survey of only 1,000 people can reach this level of accuracy? You must first assume that the survey respondents have been sampled at random from the population, meaning that people are selected one at a time, with all persons in the U.S. being equally likely to be picked at each point. For most polls, this is approximated by calling phone numbers generated randomly by computer. The margin of error is a mathematical abstraction, and there are a number of reasons why actual errors in surveys are larger. Finally, the 3 percent margin of error is an understatement because opinions change ... A poll is a snapshot, not a forecast. Other keywords and phrases -- margin of error, opinion, poll, sample size, survey -- from the text of the article) Scientific American (March 15, 2004): published online. **The complete text of the article is available at http://www.sciam.com/askexpert_question.cfm?articleID=0009A260-B037-1047-AD4683414B7F0000&ref=sciam (the Web site of Scientific American)** How to find the above journal, magazine, or other publication? See Step 3: Locate of the Information Strategy for details. Questions? Please let me know. |
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