es.ppt

Polls predicting 1992 . presidential election es
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Polls predicting 1996 . presidential election es
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How many interviews it took to estimate the behaviors of 90 million voters?
Less than 2,000
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The History of Sampling
In 1920, Literary Digest mailed postcards to people in 6 states, asking whom they were planning to vote for in the presidential campaign.
The Digest correctly predicted that Harding would be elected.
In the elections that followed, the Literary Digest expanded the size of its poll and made correct predictions in 1924, 1928, 1932.
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The History of Sampling
In 1936, Literary Digest conducted its most ambitious poll: 10 million ballots were sent to people listed in the telephone directories and on lists of automobile owners.
Over 2 million responded, given the Republican contender Alf London, a 57 to 43 percent landslide over the incumbent, president Roosevelt.
Election results: Roosevelt won 61% of the votes.
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The History of Sampling
Problem: 22% return rate.
A part of the answer to these questions lay in the sampling frame used by the Digest: telephone subscribers and automobile owners.
Such a design selected a disproportionately wealthy sample.
The sample effectively excluded poor people, and the poor people predominantly voted for Roosevelt’s New Deal recovery program during the depression period.
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The History of Sampling
In the same year (1936), e Gallup correctly predicted that Roosevelt would beat London.
Gallup’s ess in 1936 hinged on his use of quota sampling, which is based on a knowledge of the characteristics of the population being sampled. People are selected to match the population characteristics.
Using quota sampling, Gallup essfully predicting the presidential winner in 1940 and 1944.
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The History of Sampling
In 1948, Gallup mistakenly picked Thomas Dewey over incumbent president Harry Truman.
Factors accounted for 1948’s failure:
1). Most of the pollsters stopped polling in early Oct despite a st