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Sampling Methods Dr. Farzin Madjidi Pepperdine University Graduate School of Education and Psychology

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2 Sampling Methods Why take samples? Terminology: zUniverse zPopulation zSample zSubjects/Analysis Units zSampling Frame

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3 Sampling Methods zProbability Sampling yUsed to generate “random/non-biased) samples required for conducting inferential analyses zNon-probability Sampling yUsed mostly in qualitative analysis when the inferences are not sought

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4 Methods of Sampling zProbability Sampling ySimple Random yComplex or Systematic yStratified (proportional/disproportional) yCluster

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5 Probability Sampling All subjects have the same non-zero chance of being selected zSimple random Sampling ySample selected by a lottery yBest chance of eliminating selection bias yAdvantages and disadvantages

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6 Probability Sampling Complex/Systematic Sampling yStart with the sampling frame yRandom start yDecide on a selection strategy xEx: population of 10,000 xNeed a sample of 200 x10,000/200=50; Select every 50th name yAdvantages and Disadvantages

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7 Probability Sampling Stratified Sampling yStratify the sampling frame by some requirement into subgroups yRandomly survey within every strata(proportional/disproportional) yEx: xFirst stratify by age, within each age subgroup, you may stratify by sex and within in each resulting subgroup, conduct random sampling

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8 Probability Sampling Cluster Sampling yGenerally used when there is not an exhaustive list of all sample elements yRandomly select large clusters of your subjects (single/multi-staged) yWithin each cluster, randomly select subjects

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9 Probability Sampling zSample Size yUniformity/homogeneity of population ySize of population yDegree of confidence sought y Maximum tolerable error zRequire formula and/or tables

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10 Non-probability Sampling zHomogeneous yLook for uniformity within/among groups or subjects zMaximum Variation yLook for for a variety of subjects that identify important common patterns zTheoretical yLook for subjects/behaviors that exemplify theoretical constructs

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11 Non-probability Sampling zTypical Case yLook for a case that represents the norms zCritical Case yLook for a case that uniquely represent the key issues zIntensity yLook for cases that are information rich, but not extreme

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12 Non-probability Sampling zPolitically Important Cases yLook for the cases that attract attention to desired issues zExtreme (Deviant) Cases yLook for highly unusual manifestation of the desired issues zConfirming/Disconfirming Cases yElaborate on initial analysis, seek exceptions or variations

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13 zSnowball or Chain yAsk from one participant for others, who know others, … zOpportunistic yLook for unique opportunities consistent with your interest zCombination yLook for multiple cases, samples or subjects Non-probability Sampling

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14 zConvenience yLook for subjects, cases, or samples that are readily available zCriterion yLook for cases that meet a pre-described set of criteria Non-probability Sampling

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15 Non-probability Sampling zRandom purposeful yWith large purposeful samples, randomly select a subgroup zStratified Purposeful yUse stratification to sample subgroups within a large purposeful sample

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