6_stratified_sampling

6_stratified_sampling - Stratified Sampling Lecture 6 STAT...

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Unformatted text preview: Stratified Sampling Lecture 6 STAT 651: Survey Sampling Methods, Kaizar p.1/22 Lecture 6: Stratified Sampling Reading: Lohr Chapter 3, sections 1-5 Definitions and Notation Why stratify? Bias and Variance Sample allocation STAT 651: Survey Sampling Methods, Kaizar p.2/22 Motivating Example Goal: Estimate the average income of OSU graduate students one year past graduation. How? SRS of graduated students. Ask each alum their salary. target population: observation unit: sampling frame: sampling unit: sampled population: STAT 651: Survey Sampling Methods, Kaizar p.3/22 Motivating Example, cont. y = sample average V [ y ] = parenleftBig 1- n N parenrightBig S 2 y n Is there a sampling plan that would get us a better estimate without increasing the sample size? Suggest some strata? STAT 651: Survey Sampling Methods, Kaizar p.4/22 Stratified Random Sampling To estimate a population average: 1. Divide the sampling frame into groups (strata) 2. Conduct a SRS within each group 3. Estimate the average for each group (stratum) 4. Take a weighted average of the group averages STAT 651: Survey Sampling Methods, Kaizar p.5/22 Strata Strata: 1. are a partition of the population Non-overlapping Constitute the whole population 2. Must be defined (partitioned) before sampling Stratification variable should be related to the variable(s) of interest....
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6_stratified_sampling - Stratified Sampling Lecture 6 STAT...

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