copyright © 2009 pearson education, inc. publishing as longman. the 1936 literary digest...

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 LineberryGovernment in America: People, Politics, and

PolicyFourteenth Edition


1936 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.


1936 Literary Digest Poll

. . . but not this time!– Anyone remember President Landon?– Roosevelt wins 62% of the vote.

Why did it go wrong?


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.


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).


SamplingPopulation Value: 84%

Num

ber

of S

ampl

es w

ith S

ampl

e V

alue

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!


SamplingPopulation Value: 84%

Num

ber

of S

ampl

es w

ith S

ampl

e V

alue

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.


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.


Poll BiasesResponse 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.


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.


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.


1936 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

1936.

– The wealthy were more likely to support Landon.• Many Roosevelt supporters were not

included in the poll.


1936 Literary Digest PollA 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.

copyright © 2009 pearson education, inc. publishing as longman. the 1936 literary digest...

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