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SAMPLING METHODS Stratification and Clustering Richard L. Scheaffer University of Florida

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Presentation on theme: "SAMPLING METHODS Stratification and Clustering Richard L. Scheaffer University of Florida"— Presentation transcript:

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2 SAMPLING METHODS Stratification and Clustering Richard L. Scheaffer University of Florida

3 The Sampling Process Population Sampling Unit Sampling Frame Sampling Design Sample

4 …and Process Failures Sampling errors Non-sampling errors*

5 PSI Example

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7 SIMPLE RANDOM SAMPLING

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9 STRATIFIED RANDOM SAMPLING Stratified sampling designs: Convenience (administration efficiency) Estimates desired for each of the strata Reduced variation (statistical efficiency)

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13 CLUSTER SAMPLING Commonly used when: Frame for elements is relatively difficult to obtain Frame for clusters of elements of elements is relatively easy to obtain Examples: Classrooms versus students City blocks versus residents Cartons of items stored in a warehouse versus individual items

14 Examples of Clusters Polls (home or workplace) Crop yield surveys (trees, corn, sugar cane) Animal studies (traps, colonies) Systematic sample

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18 Two-stage cluster sampling with equal cluster sizes

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21 FIGURE 1: Distribution of class GPA s

22 FIGURE 2: Distribution of sample means from simple random sampling

23 FIGURE 3: GPA S by gender

24 FIGURE 4: Distribution of sample means from stratified random sampling

25 FIGURE 5: Distribution of sample means from cluster sampling; ordered clusters

26 FIGURE 6: Distribution of sample means from cluster sampling; random clusters

27 FIGURE 7: Distribution of sample means from cluster sampling; systematic clusters

28 Summary Chart

29 Names to Explore P. C. Mahalanobis –"The I.S.I. has taken the lead in the original development of the technique of sample surveys, the most potent fact finding process available to the administration". R. A. Fisher Walter Shewhart Jerzy Neyman William Cochran Edwards Deming Warren Mitofsky

30 References Groves, Robert; Dillman, Donald; Eltinge, John; and Little, Roderick, editors Survey Nonresponse. New York: Wiley. Lohr, S Sampling: Design and Analysis, Pacific Grove, CA: Brooks Cole. Scheaffer, Richard; Mendenhall, William; and Ott, R. Lyman Elementary Survey Sampling, 5 th ed. Belmont,CA: Duxbury Press.

31 EXTRAS!

32 Equal cluster sizes- comparison to SRS

33 For a random sample of size mn,


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