copyright © 2008 by nelson, a division of thomson canada limited chapter 14 part 4 sampling and...

Copyright © 2008 by Nelson, a division of Thomson Canada Limited

Chapter

14

Part 4

Sampling and Data Collection

SAMPLING DESIGNS AND SAMPLING PROCEDURES

LEARNING OBJECTIVESLEARNING OBJECTIVESLEARNING OBJECTIVESLEARNING OBJECTIVES

1. To define the terms sample, population, population element, and census

2. To explain why a sample rather than a complete census may be taken

3. To discuss the issues concerning the identification of the target population and the selection of a sampling frame

4. To discuss common forms of sampling frames and sampling frame error

5. To distinguish between random sampling and systematic (nonsampling) errors

What you will learn in this chapter

Copyright © 2008 by Nelson, a division of Thomson Canada Limited 14–1

LEARNING OBJECTIVES (cont’d)LEARNING OBJECTIVES (cont’d)LEARNING OBJECTIVES (cont’d)LEARNING OBJECTIVES (cont’d)

6. To explain the various types of systematic (nonsampling) errors that result from sample selection

7. To discuss the advantages and disadvantages of the various types of probability and nonprobability samples

8. To understand how to choose an appropriate sample design

What you will learn in this chapter


• SampleSampleA subset, or some part, of a larger population

• Population (universe)Population (universe)Any complete group of entities that share some

common set of characteristics

• Population elementPopulation elementAn individual member of a population

• CensusCensusAn investigation of all the individual elements that

make up a population

Sampling TerminologySampling TerminologySampling TerminologySampling Terminology


• Pragmatic ReasonsPragmatic ReasonsSampling cuts costs, reduces labour requirements,

and gathers vital information quickly

• Accurate and Reliable ResultsAccurate and Reliable ResultsMost properly selected samples give sufficiently

accurate resultsIf the elements of a population are quite similar, only

a small sample is necessary to accurately portray the characteristic of interest

Why Sample?Why Sample?Why Sample?Why Sample?


• Defining the Target PopulationDefining the Target PopulationAnswering questions about the crucial

characteristics of the population is the usual technique for defining the target population

Practical Sampling ConceptsPractical Sampling ConceptsPractical Sampling ConceptsPractical Sampling Concepts


• The Sampling FrameThe Sampling FrameA list of elements from which a sample may be

drawn; also called working populationSampling frame error

An error that occurs when certain sample elements are not listed or are not accurately represented in a sampling frame

Sampling frames for international marketing research The availability of sampling frames around the globe varies

dramatically Not every country’s government conducts a census of

population

Practical Sampling Concepts (cont’d)Practical Sampling Concepts (cont’d)Practical Sampling Concepts (cont’d)Practical Sampling Concepts (cont’d)


• Sampling UnitsSampling UnitsSampling unit

A single element or group of elements subject to selection in the sample

Primary sampling unit (PSU) A term used to designate a unit selected in the first stage of

sampling

Secondary sampling unit A term used to designate a unit selected in the second

stage of sampling

Tertiary sampling unit A term used to designate a unit selected in the third stage of

sampling

Practical Sampling Concepts (cont’d)Practical Sampling Concepts (cont’d)Practical Sampling Concepts (cont’d)Practical Sampling Concepts (cont’d)


• Random Sampling ErrorRandom Sampling ErrorThe difference between 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 (Nonsampling) ErrorSystematic (Nonsampling) ErrorError resulting from some imperfect aspect of the

research design, such as mistakes in sample selection, sampling frame error, or nonresponses from persons who were not contacted or refused to participate

Random Sampling and Nonsampling ErrorsRandom Sampling and Nonsampling ErrorsRandom Sampling and Nonsampling ErrorsRandom Sampling and Nonsampling Errors


Random Sampling and Nonsampling Errors Random Sampling and Nonsampling Errors (cont’d)(cont’d)Random Sampling and Nonsampling Errors Random Sampling and Nonsampling Errors (cont’d)(cont’d)

• Less Than Perfectly Representative SamplesLess Than Perfectly Representative SamplesNonresponse error

The statistical differences between a survey that includes only those who responded and a perfect survey that would also include those who failed to respond


• Probability SamplingProbability SamplingA sampling technique in which every member of the

population has a known, non-zero probability of selection

• Nonprobability SamplingNonprobability SamplingA 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

Probability Versus Nonprobability SamplingProbability Versus Nonprobability SamplingProbability Versus Nonprobability SamplingProbability Versus Nonprobability Sampling


• Convenience SamplingConvenience SamplingThe sampling procedure of obtaining those people or

units that are most conveniently available

• Purposive (Judgment) SamplingPurposive (Judgment) SamplingA nonprobability sampling technique in which an

experienced individual selects the sample based on personal judgment about some appropriate characteristic of the sample member

Nonprobability SamplingNonprobability SamplingNonprobability SamplingNonprobability Sampling


• Snowball (Referral) SamplingSnowball (Referral) SamplingA sampling procedure in which initial respondents

are selected by probability methods and additional respondents are obtained from information provided by the initial respondents

Nonprobability Sampling (cont’d)Nonprobability Sampling (cont’d)Nonprobability Sampling (cont’d)Nonprobability Sampling (cont’d)


• Quota SamplingQuota SamplingA nonprobability sampling procedure that ensures

that various subgroups of a population will be represented on pertinent characteristics to the exact extent that the investigator desires

Possible sources of bias Because respondents are selected according to a

convenience sampling procedure rather than on a probability basis, the haphazard selection of subjects may introduce bias

Advantages of quota sampling Speed of data collection, lower costs, and convenience

Nonprobability Sampling (cont’d)Nonprobability Sampling (cont’d)Nonprobability Sampling (cont’d)Nonprobability Sampling (cont’d)


• Simple Random SamplingSimple Random SamplingA sampling procedure that assures each element in

the population of an equal chance of being included in the sample

Selecting a simple random sample Example: Honda

• Systematic SamplingSystematic SamplingA sampling procedure in which a starting point is

selected by a random process and then every nth number on the list is selected

Probability SamplingProbability SamplingProbability SamplingProbability Sampling


• Stratified SamplingStratified SamplingA probability sampling procedure in which simple

random subsamples that are more or less equal on some characteristic are drawn from within each stratum of the population

• Proportional versus Disproportional SamplingProportional versus Disproportional SamplingProportional stratified sample

A stratified sample in which the number of sampling units drawn from each stratum is in proportion to the population size of that stratum

Disproportional stratified sample A stratified sample in which the sample size for each

stratum is allocated according to analytical considerations

Probability Sampling (cont’d)Probability Sampling (cont’d)Probability Sampling (cont’d)Probability Sampling (cont’d)


• Cluster SamplingCluster SamplingAn 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

• Multistage Area SamplingMultistage Area SamplingSampling that involves using a combination of two or

more probability sampling techniques

Probability Sampling (cont’d)Probability Sampling (cont’d)Probability Sampling (cont’d)Probability Sampling (cont’d)


• Degree of AccuracyDegree of AccuracyThe degree of accuracy required or the researcher’s

tolerance for sampling and nonsampling error may vary from project to project, especially when cost savings or another benefit may be a trade-off for a reduction in accuracy

• ResourcesResourcesIf the researcher’s financial and human resources

are restricted, certain options will have to be eliminated

What Is the Appropriate Sample Design?What Is the Appropriate Sample Design?What Is the Appropriate Sample Design?What Is the Appropriate Sample Design?


What Is the Appropriate Sample Design? What Is the Appropriate Sample Design? (cont’d)(cont’d)What Is the Appropriate Sample Design? What Is the Appropriate Sample Design? (cont’d)(cont’d)

• TimeTimeA researcher who needs to meet a deadline or complete a

project quickly will be more likely to select a simple, less time-consuming sample design

• Advance Knowledge of the PopulationAdvance Knowledge of the PopulationAdvance knowledge of population characteristics is an

important criterionA lack of adequate lists may rule out systematic sampling

or stratified sampling, or may dictate that a preliminary study be conducted to generate information to build a sampling frame


What Is the Appropriate Sample Design? What Is the Appropriate Sample Design? (cont’d)(cont’d)What Is the Appropriate Sample Design? What Is the Appropriate Sample Design? (cont’d)(cont’d)

• National versus Local ProjectNational versus Local ProjectGeographic proximity of population elements will

influence sample design

• Need for Statistical AnalysisNeed for Statistical AnalysisThe need for statistical projections based on the

sample often is a criterion


• Web Site VisitorsWeb Site VisitorsInternet surveys may not be representative because

of the haphazard manner by which many respondents arrived at a particular Web site or because of self-selection bias

• Panel SamplesPanel SamplesDrawing a probability sample from an established

consumer panel or other prerecruited membership panel is a popular, scientific, and effective method for creating a sample of Internet users

Internet Sampling Is UniqueInternet Sampling Is UniqueInternet Sampling Is UniqueInternet Sampling Is Unique


• Recruited Recruited Ad HocAd Hoc Samples SamplesAnother means of obtaining an Internet sample is to

obtain or create a sampling frame of e-mail addresses on an ad hoc basis

Researchers may create the sampling frame offline or online

• Opt-in ListsOpt-in ListsOpt in

To give permission to receive selected e-mail, such as questionnaires, from a company with an Internet presence

Internet Sampling Is Unique (cont’d)Internet Sampling Is Unique (cont’d)Internet Sampling Is Unique (cont’d)Internet Sampling Is Unique (cont’d)


copyright © 2008 by nelson, a division of thomson canada limited chapter 14 part 4 sampling and...

Documents

sampling frame4

sampling framesampling

sampling frame error5

sample result

certain sample elements

terms sample

sample selection7

small sample