Sampling Designs and Sampling Procedures

Transcription

1 Business Research Methods 9e Zikmund Babin Carr Griffin 16 Sampling Designs and Sampling Procedures Chapter 16 Sampling Designs and Sampling Procedures 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.

2 LEARNING OUTCOMES 1. Explain reasons for taking a sample rather than a complete census 2. Describe the process of identifying a target population and selecting a sampling frame 3. Compare random sampling and systematic (nonsampling) errors 4. Identify the types of nonprobability sampling, including their advantages and disadvantages 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 16-2

3 LEARNING OUTCOMES 5. Summarize the advantages and disadvantages of the various types of probability samples 6. Discuss how to choose an appropriate sample design, as well as challenges for Internet sampling 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 16-3

4 Changing Pocketbook Problems for Today s Families Each quarter, the Gallup Corporation develops a representative sample of approximately 1,000 U.S. adults to capture public perceptions of financial concerns of the family. The most important problem facing families can often change over time Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 16-4

5 Sampling Terminology Population (universe) Any complete group of entities that share some common set of characteristics. Population Element An individual member of a population. Census An investigation of all the individual elements that make up a population. Sample A subset, or some part, of a larger population Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 16 5

6 Why Sample? Pragmatic Reasons Budget and time constraints. Limited access to total population. Accurate and Reliable Results Samples can yield reasonably accurate information. Strong similarities in population elements makes sampling possible. Sampling may be more accurate than a census. Destruction of Test Units Sampling reduces the costs of research in finite populations Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 16 6

7 Finding Out about Work Is a Lot of Work! The U.S. Census Bureau and the Bureau of Labor Statistics conduct the Current Population Survey (CPS). Uses a scientifically derived panel sample of 60,000 households. Sophisticated and detailed Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 16-7

8 EXHIBIT 16.1 Stages in the Selection of a Sample 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 16 8

9 Practical Sampling Concepts Defining the Target Population What is the relevant population? Whom do we want to talk to? Population is operationally defined by specific and explicit tangible characteristics. The Sampling Frame A list of elements from which a sample may be drawn; also called working population. Sampling Frame Error Occurs when certain sample elements are not listed or are not accurately represented in a sampling frame Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 16 9

10 EXHIBIT 16.2 Mailing List Directory Page 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

11 Practical Sampling Concepts (cont d) Sampling services (list brokers) Provide lists or databases of the names, addresses, phone numbers, and addresses of specific populations. Reverse directory A directory similar to a telephone directory except that listings are by city and street address or by phone number rather than alphabetical by last name. International Research Availability of sampling frames varies dramatically around the world Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

12 Sampling Units Sampling Unit A single element or group of elements subject to selection in the sample. Primary Sampling Unit (PSU) A unit selected in the first stage of sampling. Secondary Sampling Unit A unit selected in the second stage of sampling. Tertiary Sampling Unit A unit selected in the third stage of sampling Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

13 Random Sampling and Nonsampling Errors Random Sampling Error The difference between the sample result and the result of a census conducted using identical procedures. A statistical fluctuation that occurs because of chance variations in the elements selected for a sample. Systematic Sampling Error Systematic (nonsampling) error results from nonsampling factors, primarily the nature of a study s design and the correctness of execution. It is not due to chance fluctuation Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

14 Random Sampling and Nonsampling Errors (cont d) Less than Perfectly Representative Samples Random sampling errors and systematic errors associated with the sampling process may combine to yield a sample that is less than perfectly representative of the population Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

15 EXHIBIT 16.3 Errors Associated with Sampling 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

16 Probability versus Nonprobability Sampling Probability Sampling A sampling technique in which every member of the population has a known, nonzero probability of selection. Nonprobability Sampling A sampling technique in which units of the sample are selected on the basis of personal judgment or convenience. The probability of any particular member of the population being chosen is unknown Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

17 How Much Does Your Prescription Cost? It Depends on Who You Buy It From A survey of 200 pharmacies found that prices for the same prescription could vary as much as $100! 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

18 Nonprobability Sampling Convenience Sampling Obtaining those people or units that are most conveniently available. Judgment (Purposive) Sampling An experienced individual selects the sample based on personal judgment about some appropriate characteristic of the sample member. Quota Sampling Ensures that various subgroups of a population will be represented on pertinent characteristics to the exact extent that the investigator desires Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

19 American Kennel Club Tries to Keep Pet Owners out of the Doghouse The American Kennel Club (AKC) used quota sampling in a Dog Ownership Study. Sampled 500 dog owners and 500 nonowners. Dog owners described themselves as more laid-back and happy than non-owners Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

20 Nonprobability Sampling (cont d) Possible Sources Of Bias Respondents chosen because they were: Similar to interviewer Easily found Willing to be interviewed Middle-class Advantages of Quota Sampling Speed of data collection Lower costs Convenience 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

21 Nonprobability Sampling (cont d) Snowball Sampling A sampling procedure in which initial respondents are selected by probability methods and additional respondents are obtained from information provided by the initial respondents Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

22 Probability Sampling Simple Random Sampling Assures each element in the population of an equal chance of being included in the sample. Systematic Sampling A starting point is selected by a random process and then every nth number on the list is selected. Stratified Sampling Simple random subsamples that are more or less equal on some characteristic are drawn from within each stratum of the population Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

23 Proportional versus Disproportional Sampling Proportional Stratified Sample The number of sampling units drawn from each stratum is in proportion to the population size of that stratum. Disproportional Stratified Sample The sample size for each stratum is allocated according to analytical considerations Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

24 EXHIBIT 16.4 Disproportional Sampling: Hypothetical Example 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

25 Cluster Sampling Cluster Sampling An economically efficient sampling technique in which the primary sampling unit is not the individual element in the population but a large cluster of elements. Clusters are selected randomly Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

26 Who s at Home? Different Ways to Select Respondents Methods of generating representative samples: Full enumeration Kish method Who had last birthday? 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

27 Multistage Area Sampling Multistage Area Sampling Involves using a combination of two or more probability sampling techniques. Typically, geographic areas are randomly selected in progressively smaller (lower-population) units. Researchers may take as many steps as necessary to achieve a representative sample. Progressively smaller geographic areas are chosen until a single housing unit is selected for interviewing Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

28 EXHIBIT 16.6 Illustration of Multistage Area Sampling in the United States 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

29 EXHIBIT 16.7 Geographic Hierarchy Inside Urbanized Areas 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

30 What is the Appropriate Sample Design? Degree of accuracy Resources Time Advanced knowledge of the population National versus local project 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

31 New on Campus: Student Adjustment to College Life Stress and tension can impact students when they first arrive at school. Students were surveyed when they arrived and at the end of the first year. It s not good to engage in negative coping behaviors or have perfectionist tendencies. Better to be optimistic and socially oriented. Used a panel approach to assess change that occurred within a sample of students over time Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

32 Internet Sampling is Unique Website Visitors Internet surveys use unrestricted samples. May not be representative. Panel Samples Recruited Ad Hoc Samples Opt-in Lists 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part