Procedures. Pusanisa Thechatakerng Maejo University

Transcription

1 Sampling: Design & Procedures Ch.4 Pusanisa Thechatakerng Maejo University 1

2 The Basic of Sampling Theory (I) Population (ประชากร) The identifiable total set of elements of interest being investigated by a researcher Element/component (ส วนประกอบ) A person or object from the defined target population p from which data and information are sought (Male or female) Sampling units (กล มต วอย าง) The target population elements available for selection during the sampling process (Students, household) 2

3 The Basic of Sampling Theory (II) EX. Department t store patronage/favour project. The target population for the department store patronage project was defined as follows: Element: male or female head of the household responsible for most of the shopping at department stores Sampling units: households Extent: Amphoe Sansai 3

4 Determine the Sampling Frame Sampling frame is a representation of the elements of the target population. p It consists of a list or set of directions for identifying the target population Ex. Telephone book, an association directory listing the firms in an association, mailing list purchased from commercial organisation, a city directory 4

5 The sample size - ขนาดต วอย าง ขนาดตวอยาง The nature of the research has an impact on the sample size. Ex. Exploratory small, conclusive large. Influenced by the average size of samples in similar studies. Krejcie and Morgan (1970). Resource constrain (Time, money) 5

6 n N Sample size II 1 + Ne 2 n = ขนาดต วอย างท ควรส ม N = ประชากรท งหมด e = ความคลาดเคล อนการส ม ความคลาดเคลอนการส ม ต วอย าง ตวอยาง แทน n = 2, ,462 (0.05) 2 n = 344 คน 6

7 Sample Sizes Used in Marketing Research Studies Type of Study Minimum Size Typical Range - Problem identification research (e.g.,market potential) - Problem-solving research (e.g.,pricing) - Product tests Test marketing studies TV, Radio, or print advertising (per commercial or ad tested) - Test-market audits 10 stores stores - Focus groups 2 groups 4-12 groups 7

8 A Classification of sampling Techniques Sampling Techniques Nonprobability Probability Sampling Techniques - Exploratory Sampling Techniques Conclusive Convenience Judgmental Quota Snowball Sampling Sampling Sampling Sampling Simple Random Systematic ti Stratified Cluster Other Sampling Sampling Sampling Sampling Sampling Techniques 8

9 Nonprobability (II) Sampling Techniques - Exploratory Rely on personal judgment of researcher 1.convenience sampling Use of students, church groups, members of social, department store using charge account lists, people on street t Ex. A survey was conducted involving a convenience sample of 1,300 of fthe 1,700 student t leaders from 72 provinces who attended the 12 th annual national conference of the Nation Association of Student Councils. The survey, with 30 questions on current topics, trends, and value, found a things students considered most desirable are, a successful career, being better parent, etc 9

10 Nonprobability (II) Sampling Techniques - Exploratory 2. Judgmental sampling Chooses the elements to be included in the sample because he belives that they are representative of the population, or appropriate Ex. Judgment was used to select specify tracts, block, and household 10

11 Nonprobability (III) Sampling Techniques - Exploratory a.) Consists of developing control 3. Quotas Sampling categories or quotas, of population b) based on convenience elements (sex, age, race) or judgment Ex. Magazine readership in Metropolitan Control Characteristic Population Sample % % Num Sex Male Female 52 (100) 52 (100) 520 (1,000) Age (100) 65 (100) 650 (1,000) 11

12 Nonprobability (IV) Sampling Techniques - Exploratory 4.Snowball sampling An initial group of respondents is selected randomly. Subsequent respondents are selected based on the referrals or information provided by the initial respondents To identify buyer-seller pairs, demographic & psychographic p characteristics more similar to the person referring them 12

13 Probability (I) Sampling Techniques - Conclusive 1. Simple random (SRS) The method is equivalent to a lottery system Selecting a random, then 2. Systematic Sampling picking every ith element Ex. Sample of 1,472 of 1, 472, 000 subscribers, the sampling interval would be 1,000 (1,472,000/1,472). A number from 1 to 1,000 was drawn at random. Beginning with that number, every 1,000 th was selected. 13

14 Probability (II) Sampling Techniques - Conclusive To partition the population into subpopulations, or strata. Elements are selected from each stratum by random procedure 3. Stratified sampling p p p Ex. Because most household have annual incomes of less than 140,000 Baht. Very few households have annual incomes of 360,000 B. or more. If a simple random sample is taken, households with incomes of 360,000 or more may not be adequate represented. Stratified sampling combines the simplicity of SRS with potential gain in precision. 14

15 Probability (III) Sampling Techniques - Conclusive 4. Cluster Sampling The target population is first divided into mutually exclusive and clusters. Then, a random sample of clusters is selected, such as SRS 15

16 Discussion (I) Define the appropriate target population and the sampling frame in each of the following situations: a. The manufacturer of a new cereal brand wants to conduct in-home product usage tests in Chicago. b. A national chain store wants to determine the shopping behavior of customers who have its store charge card. c. A local TV station wants to determine households viewing habits and programming preferences. d. The local chapter of the American Marketing Association wants to test the effectiveness of its new member drive in Atlanta 16

17 Discussion (II) A manufacturer would like to survey user to determine potential for a new power press. The new press has a capacity of 500 tons and costs $225,000. It is use for forming products from lightweight and heavyweight steel and can be used by automobile, ob construction o equipment, e and the major appliance manufacturers. 17

18 Discussion (III) a. Identify the population and sampling frame that could be used. b. Describe how a simple random sample can be drawn using the identified sampling frame. c. Could a stratified sample be used? If so, how? d. Which sampling technique would you recommend? Why? 18