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Unformatted text preview: Chapter 6: Using the Normal distribution for confidence intervals and hypothesis testing for a population mean NO SPSS in this chapter! Ellen Gundlach STAT 301 Course Coordinator Purdue University What can we do with our sample data? Statistical inference : hypothesis testing and confidence intervals Population Sample (parameter) (statistic) Inference Sampling Confidence intervals allow us to estimate the population parameter Confidence interval created from our sample Population mean Where we sample SRSs and Confidence Intervals Confidence The 95% confidence refers to our method and how well it works over the long run. Applet: http://bcs.whfreeman.com/scc6e/content/cat_040/spt/confidence/confidenceinterval.html Video of me using the applet: http://www.screencast.com/users/EllenGundlach/folders/Jing/media/82da566346d140d3ba2aba3fb53dcbf2 Sample size As sample size , margin of error (width) . Confidence level As confidence level , margin of error (width) . Is a bigger CI better? Confidence level Sample size Confidence interval formulas If you know the population standard deviation, : Confidence level 90% 95% 99% Z* 1.645 1.960 2.576 * x z n Margin of error, sample size The margin of error: Know margin of error, want to know sample size: * m z n = 2 * z n m = Confidence interval example A questionnaire of drinking habits was given to a random sample of 30 fraternity members, and each student was asked to report the # of beers he had drunk in the past month. The sample resulted in an average of 22 beers with a population standard deviation of 9 beers. Give a 90% confidence interval for the population mean number of beers drunk by fraternity members in the past month. Confidence interval example Give a 90% confidence interval for the population mean number of beers drunk by fraternity members in the past month. 22, 9, 30, 90%, * 1.645 9 * 22 (1.645) 22 2.7 30 (19.3, 24.7) x n C z x z n = = = = = = = Confidence interval example How many students should you sample if you want a margin of error of 1 for a 90% confidence interval? Confidence interval example How many students should you sample if you want a margin of error of 1 for a 90% confidence interval?...
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This note was uploaded on 11/08/2010 for the course STAT 301 taught by Professor Staff during the Spring '08 term at Purdue UniversityWest Lafayette.
 Spring '08
 Staff
 Normal Distribution, Spss

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