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# Chapter 5 Stratified Random Sampling

Chapter 5 Stratified Random Sampling. Advantages of stratified random sampling How to select stratified random sample Estimating population mean and total Determining sample size, allocation Estimating population proportion; sample size and allocation Optimal rule for choosing strata.

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## Chapter 5 Stratified Random Sampling

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1. Chapter 5Stratified Random Sampling • Advantages of stratified random sampling • How to select stratified random sample • Estimating population mean and total • Determining sample size, allocation • Estimating population proportion; sample size and allocation • Optimal rule for choosing strata

2. Stratified Random Sampling • The ultimate function of stratification is to organize the population into homogeneous subsets and to select a SRS of the appropriate size from each stratum.

3. Stratified Random Sampling • Often-used option • May produce smaller BOE than SRS of same size • Cost per observation may be reduced • Obtain estimates of population parameters for subgroups • Useful when the population is heterogeneous and it is possible to establish strata which are reasonably homogeneous within each stratum

4. Chapter 5Stratified Random Sampling Improved Sampling Designs with Auxiliary Information Stratified Random Sampling Chapter 6 Ratio and Regression Estimators

5. Stratified Random Sampling: Notation

6. Stratified Random Sampling

7. Stratified Random Sampling: Estimate of Mean 

8. Stratified Random Sampling: Estimate of Mean , BOE

9. Stratified Random Sampling: Estimate of Population Total 

10. Stratified Random Sampling: BOEfor Mean  and Total , t distribution • When stratum sample sizes are small, can use t dist.

11. Degrees of Freedom(worksheet cont.)

12. Compare BOE in Stratified Random Sample and SRS (worksheet cont.) Strat. random sample has more precision

13. Approx. Sample Size to Estimate 

14. Approx. Sample Size to Estimate 

15. Summary: Approx. Sample Size to Estimate ,

16. Example: Sample Size to Estimate  (worksheet cont.)

17. Example: Sample Size to Estimate  (worksheet cont.)

18. 5.5 Allocation of the Sample • Objective: obtain estimators with small variance at lowest cost. • Allocation affected by 3 factors: • Total number of elements in each stratum • Variability in each stratum • Cost per observation in each stratum

19. 5.5 Allocation of the Sample: Proportional Allocation • If don’t have variability and cost information for the strata, can use proportional allocation. In general this is not the optimum choice for the stratum sample sizes.

20. Directly proportional to stratum size and stratum variability

21. Worksheet 11

22. Directly proportional to stratum size and stratum variability Inversely proportional to stratum cost/obs

23. Worksheet 12

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