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Chapter 4
Sample Surveys in the Real World
In this chapter
•
Types of error
•
Survey questions
•
Believing a statistic
Types of error
Sampling frame
– list of every individual in the population
Undercoverage
– when some groups in the population are left out of the sample
Example
Suppose your population is all Lexington residents and you are going to conduct phone
surveys. A list of all residents in Lexington would be your sampling frame. If you use a
phone book to make the calls this would be undercoverage. Obviously, everyone does
not have a phone.
Sampling errors
– Errors that result from sampling
•
Random sampling error – This is the error we that comes from us taking a sample we
expect this error and can calculate it. Margin of error covers only random sampling
error. (other sources of error can cause large bias)
•
Bad sampling methods – Any deviation from a random sample is a bad sampling
method which causes bias and increases the error in our estimate.
Nonsampling errors
– Errors that do not result from sampling
•
Processing error – Any data entry or arithmetic mistake.
•
Response error – Incorrect response from subject either intentionally or just because
no effort was given when taking the survey.
•
Nonresponse – This is the biggest problem with surveys. If you send out 1000
surveys, you will not typically get 1000 back.
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View Full DocumentExample
If you send out 3200 surveys and you only get back 1200, then you have a problem.
When setting up a study we make sure the sample is representative of the population.
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 Fall '10
 Bradley,W
 Statistics

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