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Business Research Methods
William G. Zikmund
Chapter 16: Sample Designs and Sampling Procedures
Sampling TerminologySamplePopulation or universePopulation elementCensus
SampleSubset of a larger population, on which data is collected
PopulationAny complete groupPeopleSales territoriesStores
CensusInvestigation of all individual elements that make up a population
Define the target populationSelect a sampling frameConduct fieldworkDetermine if a probability or nonprobability sampling method will be chosenPlan procedure for selecting sampling unitsDetermine sample sizeSelect actual sampling unitsStages in the Selectionof a Sample
Target PopulationRelevant populationMust be operationally defined
Sampling FrameA list of elements from which the sample may be drawnWorking populationMailing lists - data base marketersSampling frame error
Sampling UnitsGroup selected for the samplePrimary Sampling Units (PSU)Secondary Sampling UnitsTertiary Sampling Units
Random Sampling ErrorThe difference between the sample results and the result of a census conducted using identical proceduresStatistical fluctuation due to chance variations
Systematic Errors (Bias)Non-sampling errorsUnrepresentative sample resultsNot due to chanceDue to study design or imperfections in execution
Errors Associated with SamplingRandom sampling errorSampling frame errorNonresponse error
Two Major Categories of SamplingProbability samplingKnown, nonzero probability for every elementNonprobability samplingProbability of selecting any particular member is unknown
Probability SamplingSimple random sampleSystematic sampleStratified sampleCluster sampleMultistage area sample
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
Systematic Sampling A simple processEvery nth name from the list will be drawn
Stratified SamplingProbability sampleSubsamples are drawn within different strataEach stratum is more or less equal on some characteristicDo not confuse with quota sample
Cluster SamplingThe 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 The primary sampling unit is a larger cluster of elements located in proximity to one another
Nonprobability SamplingConvenienceJudgmentQuotaSnowball
Convenience Sampling Also called haphazard or accidental samplingThe sampling procedure of obtaining the people or units that are most conveniently available
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
Quota Sampling Ensures that the various subgroups in a population are represented on pertinent sample characteristicsTo the exact extent that the investigators desireIt should not be confused with stratified sampling.
Snowball Sampling A variety of procedures Initial respondents are selected by probability methods Additional respondents are obtained from information provided by the initial respondents
What is the Appropriate Sample Design?Degree of accuracyResourcesTimeAdvanced knowledge of the populationNational versus localNeed for statistical analysis
Internet Sampling is UniqueInternet surveys allow researchers to rapidly reach a large sample. Speed is both an advantage and a disadvantage. Sample size requirements can be met overnight or almost instantaneously. Survey should be kept open long enough so all sample units can participate.
Internet SamplingMajor disadvantage lack of computer ownership and Internet access among certain segments of the populationYet Internet samples may be representative of a target populations. target population - visitors to a particular Web site. Hard to reach subjects may participate
Web Site VisitorsUnrestricted samples are clearly convenience samplesRandomly selecting visitorsQuestionnaire request randomly "pops up" Over- representing the more frequent visitors
Panel SamplesTypically yield a high response rate Members may be compensated for their time with a sweepstake or a small, cash incentive. Database on membersDemographic and other information from previous questionnairesSelect quota samples based on product ownership, lifestyle, or other characteristics.Probability Samples from Large Panels
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