Introduction to Research Methods

Sampling & External Validity2KNR 497Research MethodsSamplingSlide 1Chapter 2

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KNR 497Research Methods:SamplingSlide 2External Validity: Critiquing1

41KNR 497Research Methods:SamplingSlide 3External Validity: CritiquingThe sampling modelGoal (claim) is representative samplingOften not attainable - Who to generalize to?Availability of the true representative sample?Will the sample be representative of other times?An alternative is to model (or critique) the differences in a systematic way

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Proximal similarity model (Campbell, 1963)321KNR 497Research Methods:SamplingSlide 4External Validity: Critiquingthis is the crux of it

1KNR 497Research Methods:SamplingSlide 5External Validity: CritiquingProximal similarity model (Campbell, 1963)The idea here is to quantify the difference between the various properties of the study you are considering, and that to which you want to generalize, and then consider the likelihood that this difference would alter the researchs findings

Critiquing and responding to (improving) external validitySampling model (depends upon)Random sample (impossible)Minimal drop outProximal similarityEvaluate, critique, consider21KNR 497Research Methods:SamplingSlide 6External Validity: Critiquing

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4321KNR 497Research Methods:SamplingSlide 7Sampling TerminologyPopulation the group to whom you wish to generalizeTheoreticalAccessibleSampling frame the listing of the accessible population from which youll draw your sample (or the procedure by which youll draw them)Sample the group of people you select to be in your study

1KNR 497Research Methods:SamplingSlide 8The Different Groups in the Sampling Model

KNR 497Research Methods:SamplingSlide 9Statistical Terms in Sampling

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KNR 497Research Methods:SamplingSlide 10The Sampling DistributionHow do you get from a sample statistic to an estimate of the population parameter?The distribution of an infinite number of samples of the same size as the sample in your studyAverage of the averages is close to the population parameterSampling distribution is theoreticalStandard error and the 65, 95, 99 percent rule4321