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## Data for Decisions Chapter 7

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**Data for DecisionsChapter 7**Austin Cole February 16, 2010**Outline**I. Sampling a. Bad Sampling Methods b. Random Sampling II. Experiments III. Applying Sample to a Population IV. Simulations V. Confidence Intervals VI. Discussion**Population- entire group of individuals about which we want**information Sample- part of population from which information is collected Sampling**Monthly unemployment rate based on survey of 60,000**households Define population Define unemployed Final percentage Unemployment**Convenience sample-sample of easiest to reach members of**population Bias-systematically favoring a certain outcome Voluntary Response Sample-people choose to respond to a general appeal Bad Sampling Methods**Every individual in population has equal chance to be**sampled Table of random digits Simple Random Sampling**Undercoverage-group of the population is left out when**choosing sample Nonresponse-individual chosen doesn’t participate Wording of questions Cautions about Sample Surveys**Observational Study**Experiment-imposes some treatment on individuals to observe their responses Confounding variables-variable whose effects cannot be distinguished Control group Experiments**Online vs. classroom courses**Randomized Comparative Experiment**1.Starting on line x, read 2-digit groups until you have**chosen 6 restaurants. 2.Ignore groups not in the range and ignore any repeated labels. Random Sampling Exercise • Starting at line 105: 07, 19, 14, 17, 13, 15**Placebo effect**Double-blind experiment Prospective studies Thinking about Experiments**Statistical inference-using fact of a sample to estimate**about whole population Parameter-fixed number that describes population Statistic-number that describes a sample Sampling Distribution-distribution of values taken by the statistic in all possible samples of the same size from the same population From Sample to Population**Shape**Center-mean of sampling distribution (g) Spread-standard deviation of sampling distribution Assessing simulations g(1- g) n**Percent of all samples will produce an interval containing**the true population parameter 68-95-99.7 Rule Margin of error for 95% confidence interval: Confidence Intervals ĝ(1- ĝ) 2 n**A Gallup poll asked a random sample of 1785 adults if they**attended church or synagogue in the last 7 days. Of the respondents, 750 said yes. Find the 95% confidence interval. Exercise ĝ(1- ĝ) ĝ=.42 =.023 n 95% Confidence Interval: .376 to .466**Discussion**• In real world examples, what are some uses of knowing the spread/standard deviation? • Other uses/applications for this information? 9,38,44a (7th edition) Homework Problems: