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Unformatted text preview: Interval Estimation Review So far we have developed two different methods for interval estimation for a population mean: 1. The population standard deviation σ is known. ¯ x ± z α/ 2 σ √ n 2. The population standard deviation σ is not known. ¯ x ± t α/ 2 s √ n Some guidelines for using these two methods: To use the confidence interval ¯ x ± z α/ 2 σ √ n • We must know the value of σ . • The sample size should be over 30. • If the sample size is less than 30, the population distribution must be normal. To use the confidence interval ¯ x ± t α/ 2 s √ n • We do not know the value of σ . • The sample size should be above 50. • If the sample size is between 30 and 50, the population distribution should not be highly skewed and not contain any outliers. • If the sample size is less than 30, the population distribution must be normal, or close to normal. 1 Ex : A National Retail Foundation survey found households intended to spend an average of $649 during the December holiday season. Assume that thean average of $649 during the December holiday season....
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This note was uploaded on 01/24/2011 for the course STATISTICS 19897 taught by Professor Jager,abigaill during the Fall '10 term at Kansas State University.
 Fall '10
 Jager,AbigailL
 Standard Deviation

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