讲义教程说明13.sampling

1、Quantitative SamplingIan CrawfordSurvey ErrorsTotal ErrorSampling ErrorNonsampling Error Inadequate sampling frame. Poor implementation of the sampling plan. Random errors. Respondent distortions. Interviewer effects. Sponsor effects. Nonresponse.The Sampling Process Specify data to be collectedTarg

2、et populationData collection instrumentSample sizeSampling techniquesError estimationsampling framesampling unitsscreening questionsincidence ratesprobabilitynonprobabilitydesired accuracyProbability DesignsTaxonomy Of Sampling DesignsNonprobability SamplingSimple Random SamplingStratified SamplingC

3、luster SamplingProportionateAllocationOptimalAllocationQuota SamplingOne StageClusterMultistageClusterConvenience SamplingJudgementalSamplingSnowball SamplingSystematicSamplingSystematic Sampling Of Retail StoresExample Of A Table Of Random NumbersDecisions When Stratifying SamplesBasis of Stratific

4、ation - the variables to use to subdivide the population into strata.Number of strata - the number of strata to be constructed and the stratum boundaries.Sample sizes within strata - the number of observations to be taken in each stratum.Stratified Sampling - proportional allocationStratumNumber of

5、Items in StratumAB10,00090,000Sampling Fraction:Sample sizePopulation size= 0.550010,000=Stratum A (10,000 x 0.5% = 50 Stratum B (90,000 x 0.5% = 450Optimal AllocationOptimal i.e. lowest standard deviation possible.Only used when we know the S.D. in each stratum.The larger the stratum the larger the

6、 sample needed from that stratum.The strata with larger variances (SDs) are sampled more heavily.NA = 10, 000 SD = 5,000NB = 90,000 SD = 1,000Optimal sample From stratum(10,000) (5,000)_(10,000) (5,000) + (90,000) (1,000)500Sample in stratum A = 179Sample = 500Area Sampling00123456789101112131415161

7、71819202122232425262728293031323334353637Random Walks0012345678910111213141516171819202122232425262728293031323334353637Multistage Cluster SamplingStage 1: Randomly select 3regions in France .Multistage Sampling 2BrittanyStage 2: Within each regionrandomly select 5 DepartmentsMultistage Sampling 3St

8、age 3: Randomly select 4 towns/cities within eachDepartment.Stage 4: Randomly select 2 districts within each town/city.Stage 5: Randomly select 3 streets or blocks within eachtown or city district.Stage 6: Interview all households in those streets/blocks.Quota SamplingEthnic GroupShona120Ndebele20Eu

9、ropean50Other10Upper e - 60Middle e - 7Lower e - 20Lower e - 3Lower e - 10Lower e - 2Middle e - 40Middle e - 15Middle e - 3Upper e - 10Upper e - 25Upper e - 5 e LevelLocationUrban - 40Rural - 20SexFemale - 20Male - 20Statistical Sample Size Estimationn = (Z)2 (SD)2(P)2n = (Z)2 (SD)2(P)2Sample size r

10、equiredfor a given level ofaccuracySquare of theConfidence intervalSquare of theStandard deviation(i.e. the variance)The square of thePrecision requiredStatistical Sample Size Estimation Examplen = (Z)2 (SD)2(P)2An exploratory study of 20 Greek students estimates that weekly alcohol consumption is 40 units with a standard deviation of +/- 10 units. This is considered to be too inac