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Learning Math Home
Data Measurement and Variation
 
Session 1 Part A Part B Part C Part D Homework
 
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B C D

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Notes for Session 1, Part D


Note 4

A voter poll taken during the 1936 presidential election provides a good example of the danger of biased sampling. The magazine Literary Digest sent a survey to 10 million Americans to determine how they would vote in the upcoming election between Democrat Franklin Roosevelt and Republican Alf Landon. More than two million Americans responded to this poll, and 60% supported Landon. The magazine published these findings, suggesting that Landon was guaranteed to win the election.

Despite the findings of the poll, however, Roosevelt defeated Landon in one of the largest landslide presidential elections ever. What happened? The sample used in the Literary Digest poll -- a sample collected through magazine subscription lists, lists of car owners, and telephone directories -- was not representative. Not all Americans at this time owned cars, had telephones, or subscribed to magazines. Moreover, Democrats were much less likely to own a car or have a telephone, and thus were less likely to be included in the sample. As a result, the sample was not representative, and the poll did not predict the outcome of the election.

<< back to Part D: Bias in Sampling


 

Note 5

  

Good sampling practices rely on some form of random selection in order to remove the bias caused by human involvement in the selection process. The Interactive Activity in Part D is intended to demonstrate how human selection might result in biased results. You are asked to select a sample of five circles from a population of 60 circles in order to estimate the size of the circles in the entire population. You will then compare the accuracy of your sample with the accuracy of a random sample. A bias should appear: Most people tend to pick a sample that greatly overestimates the size of the circles.

<< back to Part D: Bias in Sampling


 

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