Bài giảng Business Research Methods - Chapter 14: Sampling

SamplingChapter 14Learning ObjectivesUnderstand . . .The two premises on which sampling theory is based.The accuracy and precision for measuring sample validity.The five questions that must be answered to develop a sampling plan.Learning ObjectivesUnderstand . . . The two categories of sampling techniques and the variety of sampling techniques within each category.The various sampling techniques and when each is used.Pull Quote“We have to hear what’s being said in a natural environment, and social media is an obvious place to do this, but we also have to go and discover the opinions that are not being openly shared. Only then can we understand the dichotomy between the public and private persona.”Ben Leet, sales directoruSampThe Nature of Sampling Population Population Element Sampling Frame Census SampleWhy Sample?Greater accuracyAvailability of elementsGreater speedSampling providesLower costWhat Is a Sufficiently Large Sample?“In recent Gallup ‘Poll on polls,’ . . . When asked about the scientific sampling foundation on which polls are based . . . most said that a survey of 1,500 – 2,000 respondents—a larger than average sample size for national polls—cannot represent the views of all Americans.”Frank Newport The Gallup Poll editor in chiefThe Gallup OrganizationWhen Is a Census Appropriate?NecessaryFeasibleWhat Is a Valid Sample?AccuratePreciseSampling Design within the Research ProcessTypes of Sampling DesignsElement SelectionProbabilityNonprobabilityUnrestrictedSimple randomConvenienceRestrictedComplex randomPurposiveSystematicJudgmentClusterQuotaStratifiedSnowballDoubleSteps in Sampling DesignWhat is the target population?What are the parameters of interest?What is the sampling frame?What is the appropriate sampling method?What size sample is needed?When to Use Larger Sample?Desired precisionNumber of subgroupsConfidence levelPopulation varianceSmall error rangeSimple RandomAdvantages Easy to implement with random dialingDisadvantagesRequires list of population elementsTime consumingLarger sample neededProduces larger errorsHigh costSample FrameList of elements in populationComplete and correctError rate increases over timeMay include elements that must be screened outInternational frames most problematicHow to Choose a Random SampleSystematicAdvantagesSimple to designEasier than simple randomEasy to determine sampling distribution of mean or proportionDisadvantagesPeriodicity within population may skew sample and resultsTrends in list may bias resultsModerate costStratifiedAdvantagesControl of sample size in strataIncreased statistical efficiencyProvides data to represent and analyze subgroupsEnables use of different methods in strataDisadvantagesIncreased error if subgroups are selected at different ratesEspecially expensive if strata on population must be created High costCluster AdvantagesProvides an unbiased estimate of population parameters if properly doneEconomically more efficient than simple randomLowest cost per sampleEasy to do without listDisadvantagesOften lower statistical efficiency due to subgroups being homogeneous rather than heterogeneousModerate costStratified and Cluster SamplingStratifiedPopulation divided into few subgroupsHomogeneity within subgroupsHeterogeneity between subgroupsChoice of elements from within each subgroupClusterPopulation divided into many subgroupsHeterogeneity within subgroupsHomogeneity between subgroupsRandom choice of subgroups Area SamplingWell defined political or geographical boundariesLow costFrequently usedDouble SamplingAdvantagesMay reduce costs if first stage results in enough data to stratify or cluster the populationDisadvantagesIncreased costs if discriminately usedNonprobability SamplesCostFeasibilityTimeNo need to generalizeLimited objectivesNonprobability Sampling MethodsConvenienceJudgmentQuotaSnowballKey TermsArea samplingCensusCluster samplingConvenience samplingDisproportionate stratified samplingDouble samplingJudgment samplingMultiphase samplingNonprobability samplingPopulationPopulation elementPopulation parametersPopulation proportion of incidenceProbability samplingKey TermsProportionate stratified samplingQuota samplingSample statisticsSamplingSampling errorSampling frameSequential samplingSimple random sampleSkip intervalSnowball samplingStratified random samplingSystematic samplingSystematic varianceAdditional Discussion opportunitiesChapter 14Snapshot: Ford’s New SampleDealers control 75% of advertisingRecruited 30 influential dealersMorpace conducted focus groups72-hour marathon of questionsGave voice to important groupSnapshot: Research for GoodPicProfile: Mixed-Access SamplingCloseUp: Keynote ExperimentCloseUp: Keynote Experiment (cont.)Pull Quote“The proof of the pudding is in the eating. By a small sample we may judge of the whole piece.”Miguel de Cervantes Saavedra authorPulsePoint: Research Revelation80The average number of text messages sent per day by American teens.SamplingChapter 14Photo AttributionsSlideSource5©Ocean/Corbis9Chris Satttlberger/Getty Images12Jochen Sands/Getty Images 13Getty Images15KidStock/Getty Images23Ryan McVay/Getty Images24Photodisc/Getty Images28David and Les Jacobs/Blend Images