COMM88 - 0428

COMM88 - 0428 - Communication 88 4/28/09 Sampling...

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Communication 88 4/28/09 Sampling Representative Sampling (probability sampling) -Representative because everyone in population has equal chance of being included in sample -Sampling Error: -Sample data will be slightly different from population because of chance alone -Estimate this statistically (margin of error) -Smaller margin of error if: -more homogeneous population -Larger sample size -Systematic Error (sampling bias): -Systematically over- or under-represent certain segments of population -Caused by: -Improper weighting; very low response rate -Using non-representative sampling methods Representative Sampling Techniques -Simple random sampling Select elements randomly from population -List populations: random #’s table -phones: random-digit dialing -Systematic sampling From a list of the population, select every “n th ” element Must have random start ; cycle through entire list -Similar results as SRS -But watch out for potential “periodicity” -Stratified Sampling Divide population into subsets (“strata”), then select randomly from each
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COMM88 - 0428 - Communication 88 4/28/09 Sampling...

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