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Data for Decisions Chapter 7

Data for Decisions Chapter 7

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Data for Decisions Chapter 7

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  1. Data for DecisionsChapter 7 Austin Cole February 16, 2010

  2. 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

  3. Population- entire group of individuals about which we want information Sample- part of population from which information is collected Sampling

  4. Monthly unemployment rate based on survey of 60,000 households Define population Define unemployed Final percentage Unemployment

  5. "Labor Force"

  6. 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

  7. Every individual in population has equal chance to be sampled Table of random digits Simple Random Sampling

  8. Undercoverage-group of the population is left out when choosing sample Nonresponse-individual chosen doesn’t participate Wording of questions Cautions about Sample Surveys

  9. Observational Study Experiment-imposes some treatment on individuals to observe their responses Confounding variables-variable whose effects cannot be distinguished Control group Experiments

  10. Online vs. classroom courses Randomized Comparative Experiment

  11. 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

  12. Placebo effect Double-blind experiment Prospective studies Thinking about Experiments

  13. 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

  14. Simulation

  15. Shape Center-mean of sampling distribution (g) Spread-standard deviation of sampling distribution Assessing simulations g(1- g) n

  16. 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

  17. 95% Confidence Interval

  18. 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

  19. 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: