Ch. 16 SAMPLING DESIGNS AND SAMPLING PROCEDURES

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1 Ch. 16 SAMPLING DESIGNS AND SAMPLING PROCEDURES Dr. Werner R. Murhadi

2 Sampling Terminology Sample is a subset, or some part, of a larger population. population (universe) is any complete group of entities that share some common set of characteristics. population element is an individual member of a population. Census is an investigation of all the individual elements that make up a population.

3 Why Sample? Pragmatic Reason: Applied business research projects usually have budget and time constraints. Accurate and Reliable Results: see figure

4 Practical Sampling Concepts sampling frame A list of elements from which a sample may be drawn; also called working population. sampling unit A single element or group of elements subject to selection in the sample.

5 Random Sampling and Nonsampling Errors Random sampling error is The difference between the sample result and the result of a census conducted using identical procedures. Random sampling error is a function of sample size. As sample size increases, random sampling error decreases. Systematic (nonsampling) errors result from onsampling factors, primarily the nature of a study s design and the correctness of execution.

6 Total Error Random Sampling Error, occur because the particular sample selected is an imperfect representation of the population of interest Response Error Nonsampling Error Nonresponse Error Researcher Error Interviewer Error Respondent Error Surrogate Information Error Measurement Error Population Definition Error Sampling Frame error Data Analysis error Respondent Selection Error Questioning Error Recording Error Cheating error Inability Error Unwillingness Error

7 Sampling frame errors eliminate some potential respondents. Random sampling error (due exclusively to random, chance fluctuation) may cause an imbalance in the representativeness of the group. Additional errors will occur if individuals refuse to be interviewed or cannot be contacted.

8 Probability versus Nonprobability Sampling probability sampling is A sampling technique in which every member of the population has a known, nonzero probability of selection. nonprobability sampling is 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.

9 Sampling technique Nonprobability Probability Convenience/ Haphazard/ Accidental Judgmental/ Purposive Quota Snowball Simple Random Systematic Stratified Cluster Others Proportionate Disproportionate

10 Convenience Sampling Also called haphazard or accidental sampling The sampling procedure of obtaining the people or units that are most conveniently available (people passing in a mall).

11 Judgment Sampling Also called purposive sampling An experienced individual selects the sample based on his or her judgment about some appropriate characteristics required of the sample member (CPI Consumer Price Index).

12 Quota Sampling Ensures that the various subgroups in a population are represented on pertinent sample characteristics (Brand of DVD owners ie. Sony, Samsung, Toshiba ) To the exact extent that the investigators desire It should not be confused with stratified sampling.

13 Snowball Sampling A variety of procedures Initial respondents are selected by probability methods Additional respondents are obtained from information provided by the initial respondents (Buyers of more than 50 DVDs per year).

14 Simple Random Sampling A sampling procedure that ensures that each element in the population will have an equal chance of being included in the sample (Lottery)

15 Systematic Sampling A simple process Initial random point Every n-th name from the list will be drawn

16 Stratified Sampling Probability subsample in each strata Subsamples are drawn within different strata or groups Each stratum is more or less equal on some characteristic Do not confuse with quota sample

17 Cluster Sampling The purpose of cluster sampling is to sample economically while retaining the characteristics of a probability sample. The primary sampling unit is no longer the individual element in the population (ie. Cities, universities, career) The primary sampling unit is a larger cluster of elements located in proximity to one another

18 What is the Appropriate Sample Design? Degree of accuracy Resources Time Advanced knowledge of the population National versus local Need for statistical analysis

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