101 Ch. 12 - Chapter 12 Sample Surveys 1 Idea 1 Take a...

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1 Chapter 12 Sample Surveys
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2 Idea 1: Take a sample Population Group of people we want information from Examples: » Registered voters in US » ISU undergraduates Generally large Impractical or too expensive to talk to everyone
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3 Idea 1: Take a Sample Sample Smaller group of people from population Examples: » 200 registered voters » 100 ISU undergrads Group we get information from Want sample to be representative of population
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4 Idea 2: Select the Sample Randomly Controls for factors that you know in the data Examples: Gender, Race, Religion, etc. Controls for factors you don’t know in data Allows you to make inferences about Population The point of Statistics Without random selection, your sample does not tell you anything about population
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5 Idea 3: Sample Size Matters Size of sample matters Usually need a couple of hundred Size of population doesn’t matter Fraction of the population sampled is not important!
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6 Terminology Information (what do we want to know?) Examples: Percent of Registered Voters that would vote for a candidate. Mean age of ISU undergraduates Population Parameter Percent of all registered voters that will vote for a candidate Mean age of all ISU undergrads Sample Statistic Percent of the sample that will vote for a candidate Mean age of sample
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7 Parameters and Statistics Most common parameters and statistics Name Statistic Parameter Mean μ Std. Dev. s σ Proportion p Correlation r ρ y p ˆ
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8 How Do You Sample Randomly? Some might want every population member
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This note was uploaded on 03/30/2008 for the course STAT 101 taught by Professor Graham during the Spring '08 term at Iowa State.

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101 Ch. 12 - Chapter 12 Sample Surveys 1 Idea 1 Take a...

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