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Data for DecisionsChapter 7
Austin ColeFebruary 16, 2010
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Outline
I. Samplinga. Bad Sampling Methodsb. Random Sampling
II. ExperimentsIII. Applying Sample to a PopulationIV. SimulationsV. Confidence IntervalsVI. Discussion
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Sampling
Population- entire group of individuals about which we want informationSample- part of population from which information is collected
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Unemployment
Monthly unemployment rate based on survey of 60,000 householdsDefine populationDefine unemployedFinal percentage
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"Labor Force"
UnemployedNot looking for workEmployed
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Bad Sampling Methods
Convenience sample-sample of easiest to reach members of populationBias-systematically favoring a certain outcomeVoluntary Response Sample-people choose to respond to a general appeal
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Simple Random Sampling
Every individual in population has equal chance to be sampledTable of random
digits
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Cautions about Sample Surveys
Undercoverage-group of the population is left out when choosing sampleNonresponse-individual chosen doesn’t participateWording of questions
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Experiments
Observational StudyExperiment-imposes some treatment on individuals to observe their responsesConfounding variables-variable whose effects cannot be distinguishedControl group
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Randomized Comparative Experiment
Online vs. classroom courses
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Random Sampling Exercise
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.
Starting at line 105: 07, 19, 14, 17, 13, 15
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Thinking about Experiments
Placebo effectDouble-blind experimentProspective studies
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From Sample to Population
Statistical inference-using fact of a sample to estimate about whole populationParameter-fixed number that describes populationStatistic-number that describes a sampleSampling Distribution-distribution of values taken by the statistic in all possible samples of the same size from the same population
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Simulation
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Assessing simulations
ShapeCenter-mean of sampling distribution (g)Spread-standard deviation of sampling distribution
g(1- g)n
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Confidence Intervals
Percent of all samples will produce an interval containing the true population parameter68-95-99.7 RuleMargin of error for 95% confidence interval:
ĝ(1- ĝ)n2
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95% Confidence Interval
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Exercise
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.
ĝ(1- ĝ)n
ĝ=.42 =.023
95% Confidence Interval: .376 to .466
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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: