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Sampling 抽樣

11. Sampling 抽樣. 中央大學 . 資訊管理系 范錚強 mailto: ckfarn@mgt.ncu.edu.tw 2011.05 updated. Learning Objectives. Understand . . . The two premises on which sampling theory is based. The accuracy and precision for measuring sample validity.

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Sampling 抽樣

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  1. 11 Sampling 抽樣 中央大學.資訊管理系 范錚強 mailto: ckfarn@mgt.ncu.edu.tw 2011.05 updated

  2. Learning Objectives Understand . . . • The two premises on which sampling theory is based. • The accuracy and precision for measuring sample validity. • The five questions that must be answered to develop a sampling plan. 中央資管：范錚強

  3. Learning Objectives Understand . . . • The two categories of sampling techniques and the variety of sampling techniques within each category. • The various sampling techniques and when each is used. 中央資管：范錚強

  4. What Is a Sufficiently Large Sample? “In recent Gallup ‘Poll on polls,’ . . . When asked about the scientific sampling foundation on which polls are based . . . most said that a survey of 1,500 – 2,000 respondents—a larger than average sample size for national polls—cannot represent the views of all Americans.” Frank Newport, The Gallup Poll editor in chief, The Gallup Organization 中央資管：范錚強

  5. The Nature of Sampling • Sampling • Population Element • Population • Census • Sampling frame 中央資管：范錚強

  6. Greater speed Why Sample? Availability of elements Lower cost Sampling provides Greater accuracy 中央資管：范錚強

  7. When Is a Census Appropriate? Feasible Necessary 中央資管：范錚強

  8. What Is a Valid Sample? Accurate Precise 中央資管：范錚強

  9. 規劃樣本 目標母體 實際達成的樣本 正式描述 實際達成的母體 外部效度 External Validity 中央資管：范錚強

  10. Types of Sampling Designs 中央資管：范錚強

  11. Steps in Sampling Design What is the target population? What are the parameters of interest? What is the sampling frame? What is the appropriate sampling method? What size sample is needed? 中央資管：范錚強

  12. Population variance Desired precision Number of subgroups Confidence level Small error range When to Use Larger Sample Sizes? 中央資管：范錚強

  13. Advantages Easy to implement with random dialing Disadvantages Requires list of population elements Time consuming Uses larger sample sizes Produces larger errors High cost Simple Random 中央資管：范錚強

  14. Advantages Simple to design Easier than simple random Easy to determine sampling distribution of mean or proportion Disadvantages Periodicity within population may skew sample and results Trends in list may bias results Moderate cost Systematic 中央資管：范錚強

  15. Advantages Control of sample size in strata Increased statistical efficiency Provides data to represent and analyze subgroups Enables use of different methods in strata Disadvantages Increased error will result if subgroups are selected at different rates Especially expensive if strata on population must be created High cost Stratified 中央資管：范錚強

  16. Advantages Provides an unbiased estimate of population parameters if properly done Economically more efficient than simple random Lowest cost per sample Easy to do without list Disadvantages Often lower statistical efficiency due to subgroups being homogeneous rather than heterogeneous Moderate cost Cluster 中央資管：范錚強

  17. Stratified Population divided into few subgroups Homogeneity within subgroups Heterogeneity between subgroups Choice of elements from within each subgroup Cluster Population divided into many subgroups Heterogeneity within subgroups Homogeneity between subgroups Random choice of subgroups Stratified and Cluster Sampling 中央資管：范錚強

  18. Time Nonprobability Samples No need to generalize Feasibility Limited objectives Cost 中央資管：范錚強

  19. Nonprobability Sampling Methods Convenience Judgment Quota Snowball 中央資管：范錚強

  20. 特殊的設計考量 • 你的對象 • 個人？ • 企業？ • 企業裡的個人 • 誰？ • 是否能代表企業？ 中央資管：范錚強

  21. 複雜的設計 • 有一些構念是企業（團對、組織…） • 有一些構念是個人 • 甚至是不同的個人 • Matching • 事後配對 • 發給 CEO 和 CIO，針對回卷比對 • 事前配對 • 設計時就想好如何搭配 中央資管：范錚強

  22. 萬一要衡量的變數是有「社會正確」答案的 • 社會正確？ • 你會不會照顧團體利益？ • 你會不會非法 copy 軟體？ • 你會不會不顧一切，堅持己見？ • 得到的結果嚴重偏誤 • 如何能使得偏誤能降低 • 用兩端有張力的故事情節，挑選角色和看法 中央資管：范錚強

  23. Appendix 14a Determining Sample Size 中央資管：范錚強

  24. Random Samples 中央資管：范錚強

  25. Increasing Precision 中央資管：范錚強

  26. Confidence Levels & the Normal Curve 中央資管：范錚強

  27. Standard Errors 中央資管：范錚強

  28. Central Limit Theorem 中央資管：范錚強

  29. Estimates of Dining Visits 中央資管：范錚強

  30. Calculating Sample Size for Questions involving Means Precision Confidence level Size of interval estimate Population Dispersion Need for FPA 中央資管：范錚強

  31. Metro U Sample Size for Means 中央資管：范錚強

  32. Proxies of the Population Dispersion • Previous research on the topic • Pilot test or pretest • Rule-of-thumb calculation • 1/6 of the range 中央資管：范錚強

  33. Metro U Sample Size for Proportions 中央資管：范錚強

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