Copyright © 2009 Pearson Education, Inc. Publishing as Longman. The 1936 Literary Digest Presidential Election Poll Case Study: Special Topic Lecture Chapter 6: Public Opinion and Political Action Edwards, Wattenberg, and Lineberry Government in America: People, Politics, and Policy Fourteenth Edition

Copyright © 2009 Pearson Education, Inc. Publishing as Longman Literary Digest Poll Poll Process –Sample of 10,000,000 people, drawn from telephone books and motor vehicle registrations, were sent postcards. 2.3 million responded. –Predicts Alf Landon will win in 1936, 57% to 43%. –Literary Digest had been right in every previous election.

Copyright © 2009 Pearson Education, Inc. Publishing as Longman Literary Digest Poll... but not this time! –Anyone remember President Landon? –Roosevelt wins 62% of the vote. Why did it go wrong?

Copyright © 2009 Pearson Education, Inc. Publishing as Longman. Sampling A small sample closely approximates the whole population if randomly chosen. –Population: the group about which a poll is seeking information. Citizens, registered voters, likely voters, women between the ages of 18 and 25, etc. –Sample: a subset of the poll’s population to whom the questions are actually asked. –Random sample: everyone in the poll population is equally likely to be included in the sample.

Copyright © 2009 Pearson Education, Inc. Publishing as Longman. Sampling Random sample: everyone in the poll population is equally likely to be included in the sample. –Random digit dialing is the most common solution, especially for political polls. –Choosing every fourth voter leaving a supermarket is random for some populations (grocery consumers) but not others (registered voters).

Copyright © 2009 Pearson Education, Inc. Publishing as Longman. Sampling Population Value: 84% Number of Samples with Sample Value 84% Sample Values 74%79%89%94% Larger samples are more accurate. –As samples get larger, a higher percentage resemble the population. –There is a limit (2,000 is a common figure). –Population size has no effect!

Copyright © 2009 Pearson Education, Inc. Publishing as Longman. Sampling Population Value: 84% Number of Samples with Sample Value 84% Sample Values 74%79%89%94% Margin of Error –Measures the level of confidence in the findings of a public opinion poll. –Expressed as the range within which the population value lies: +/- 3%. –90% of the time, the population value is within 3 points above or below the sample value.

Copyright © 2009 Pearson Education, Inc. Publishing as Longman. Poll Biases Poll processes can undermine accuracy. Sample Bias –Not everyone in the population is equally likely to be in the sample. –In-person election polling at a mall: not all voters are equally likely to shop at a mall. –People with only cell phones are a growing problem for pollsters.

Copyright © 2009 Pearson Education, Inc. Publishing as Longman. Poll Biases Response Bias –Not everyone is equally likely to respond to a poll. Minorities and people with low trust in government may not respond to pollsters. People with strong opinions are more likely to respond than people who don’t care. –Oversampling as a solution. Including more of such groups in the sample can ensure that they are represented in proportion to their portion of the population.

Copyright © 2009 Pearson Education, Inc. Publishing as Longman. Poll Biases Question Bias –Poll questions can lead people to not answer as they really feel. –Changes in question wording and order can suggest an answer. –People may give the answer that they think the pollster is seeking. –People may not admit to socially unacceptable views.

Copyright © 2009 Pearson Education, Inc. Publishing as Longman. Poll Biases Deliberately Bad Polls –Some polls are deliberately biased to get a desired result that can be used for public relations. –Entertainment polls, often on web sites, aren’t designed to get accurate information but to amuse visitors. –“Push polls” appear to be polls but are really ways to trick people into believing deceptive information.

Copyright © 2009 Pearson Education, Inc. Publishing as Longman Literary Digest Poll: What Went Wrong? A serious case of sample bias! –The wealthy were more likely to be included in the sample. Telephones and cars were luxury items in –The wealthy were more likely to support Landon. Many Roosevelt supporters were not included in the poll.

Copyright © 2009 Pearson Education, Inc. Publishing as Longman Literary Digest Poll A 2005 poll on CNN.com asked, “Is Texas ready for Hurricane Rita?” –52% of respondents said “yes.” –The sample size is 117,000. Does this reflect American opinion? –Sample Bias? Only certain groups go to news web sites. Only certain news viewers go to CNN.com. –Question Bias? –Response Bias? People who have a strong opinion are more likely to respond.