1. Representative Sampling Presented at the AWDS Task Force’s Marketing Workshop Big Sky, Montana Friday, September 20, 2002 Len Singel, AWDS Coordinator

2. Overview  Definitions  Reducing Error  Sample Creation  Examples

3. Definitions  Population – consists of all the units (individuals, households, organizations) to which you desire to generalize survey results  Sample Frame – list from which your sample is drawn

4. Definitions  Sample – the set of respondents selected from a larger population for the purpose of a survey  Completed Sample – consists of all units that return completed questionnaires (instruments)

5. Definitions  Coverage Error – results from every unit in the Survey Population not having a known, non-zero chance of being included in the sample  Sampling Error – the result of collecting data from a subset, rather than all of the members of the sampling frame

6. Avoiding Coverage Error

7. How to Reduce Coverage Error?  Make certain your list contains everyone in the Survey Population Unique, non-repeating Sampling Units  Update & Properly maintain your list  Have your list contain other information that can be used to improve your survey

8. How Large Should Your Sample be?  Sample does not have to be arbitrarily selected  ALL THAT IS REQUIRED: Knowing about your study population AND Knowing your survey objectives

9. How Large Should Your Sample Be?  Sample Size Depends On: How much sampling error can be tolerated Population size Variation of Population (50/50 or 80/20) Amount of Confidence

10. Does Size Matter

11. Small Populations Population Size Sample Size for 95 Percent Confidence + 3 % Sampling Error + 5 % Sampling Error 50/50 Split 80/20 Split 50/50 Split 80/20 Split 10092878071 500341289217165 1,000516406278198 5,000880601357234

12. Larger Populations Population Size Sample Size for 95 Percent Confidence + 3 % Sampling Error + 5 % Sampling Error 50/50 Split 80/20 Split 50/50 Split 80/20 Split 10,000964639370240 50,0001,045674381245 100,0001,056678383245 1,000,0001,066682384246

13. 3 Easy Steps to Sampling 1)Identify your Target Population 2)Put together a Population List 3)Select the Sample

14. Hey, Wait a Minute….. I DON’T KNOW HOW TO SELECT THE SAMPLE!!!

15. Sampling Methods  Probability Simple Random Sampling (SRS) Systematic Sampling  Nonprobability (Purposeful)

16. Probability Sampling Method  Simple Random Sampling (SRS) Each member of the target population has an equal chance of being selected All elements are selected randomly – CAN BE CUMBERSOME!!!  Systematic Sampling Members of the target population have an equal chance of being selected Only the first element is selected randomly; rest selected systematically (every 5 th, 10 th, …)

17. Purposeful Sampling Method  Depends on subjective judgment Selected because it is convenient or typical  All members do not have the same chance of being selected

18. Purposeful Sampling Method  Appropriate for: Exploratory Research Focus Groups Organizing Committees Building Networks  Do not use if your goal is to learn about the larger population –Results are not generalizable!!

19. Example 1: Successful Hunting Experience  Target Population: 1 million Deer Hunters  Survey Objectives: Learn about Hunting Success  Acceptable Sampling Error: + 3%  Confidence Level: 95%  Population Variation: 80/20

20. Example 1: Successful Hunting Experience  Population List: Automated Licensing Database  Sample Size: 683  Sampling Method: Systematic Sampling

21. Example 2: Female Hunter Perceptions  You know you want to study female waterfowl hunters and their satisfaction levels.  But… You do not know much about them AND You do not know your survey objectives

22. Example 2: Female Hunter Perceptions  Target Population: Female Waterfowl Hunters (n = 100?)  Survey Objectives: Explore their satisfaction levels  Acceptable Sampling Error: + 3%  Confidence Level: 95%  Population Variation: 50/50 or 80/20 ???

23. Example 2: Female Hunter Perceptions  Source: Automated Licensing Database  Sample Method: ??  Sample Size:??

24. Example 2: Female Hunter Perceptions The Solution!  Conduct Exploratory Research  Increase Sampling Error to + 10%  Hold a series of focus groups (n = 50)

25. Example 2: Female Hunter Perceptions  Enables you to… Learn about Population Variation Learn about General Characteristics Define Survey Objectives Select appropriate sample size to be surveyed.

26. Review  What does sample size depend on?  What are the 3 steps to sampling?  Does size matter?

27. Sources  Dillman, D.A. 2000. Mail and Internet Surveys: The Tailored Design Method. John Wiley & Sons, Inc. 464pp.  Salant, P. and D.A. Dillman. 1994. How to Conduct your Own Survey. John Wiley & Sons, Inc. 232pp.