MSci_609_Sampling_distribution

# MSci_609_Sampling_distribution - 2/5/2011 SAMPLING...

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2/5/2011 1 SAMPLING DISTRIBUTION INSTRUCTOR: AMER OBEIDI Suppose you’re interested in the average amount of money that students in this class (the population) 2 have on them. How would you find out?

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2/5/2011 2 In January 2006, the New York Times asked half of the 1229 adults U.S. in their sample the following 3 question: •53% After 9/11, President Bush authorized government wiretaps on some phone calls in the U.S. without getting court warrants, saying this was necessary to reduce the threat of terrorism. Do you approve or disapprove. •46% After 9/11, President Bush authorized government wiretaps on some phone calls in the U.S. without getting court warrants. Do you approve or disapprove. 4
2/5/2011 3 Zogby International Zogby International is constantly searching, testing and measuring hypotheses and principles on 5 polling and public opinion research. Working with a panel of psychologists, sociologists, computer experts, linguists, political scientists, economists, and mathematicians, we explore every nuance in language and test new methods in public opinion research. It is this investment in time and money for research and development that makes us a leader in the public opinion field. Harris/Decima Ipsos-Reid Nanos Research Why bother determining the right sample size? Wouldn’t it be better to just include everyone and 6 Wouldn t it be better to just include everyone and “sample” the entire population? Such a special sample is called a census.

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2/5/2011 4 The physical impossibility of checking all items in the population. 7 The cost of studying all the items in a population. The sample results are usually adequate. Contacting the whole population would often be time-consuming. The destructive nature of certain tests The destructive nature of certain tests. 8
2/5/2011 5 Sample frame: the set of all sampling units (i.e., members, people) that have a chance to be selected. 9 A sample can only be representative of the population in the sample frame.

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## MSci_609_Sampling_distribution - 2/5/2011 SAMPLING...

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