Bài giảng Business Research Methods - Chapter 14: Determining Sample Size

Determining Sample SizeAppendix 14aMcGraw-Hill/IrwinCopyright © 2014 by The McGraw-Hill Companies, Inc. All rights reserved.Random SamplesIncreasing PrecisionConfidence Levels & the Normal CurveStandard ErrorsStandard Error(Z score)% of AreaApproximate Degree of Confidence1.0068.2768%1.6590.1090%1.9695.0095%3.0099.7399%Central Limit TheoremμμCentral Limit TheoremCentral Limit TheoremEstimates of Dining VisitsConfidenceZ score% of AreaInterval Range (visits per month)68%1.0068.279.48-10.5290%1.6590.109.14-10.8695%1.9695.008.98-11.0299%3.0099.738.44-11.56Calculating Sample Size for Questions involving MeansPrecisionConfidence levelSize of interval estimatePopulation DispersionNeed for FPAMetro U Sample Size for MeansStepsInformationDesired confidence level95% (z = 1.96)Size of the interval estimate .5 meals per monthExpected range in population0 to 30 mealsSample mean10Standard deviation4.1Need for finite population adjustmentNoStandard error of the mean.5/1.96 = .255Sample size(4.1)2/ (.255)2 = 259Proxies of the Population DispersionPrevious ResearchPilot or PretestRule-of-thumb: 1/6 of rangeMetro U Sample Size for ProportionsStepsInformationDesired confidence level95% (z = 1.96)Size of the interval estimate .10 (10%)Expected range in population0 to 100%Sample proportion with given attribute30%Sample dispersionPq = .30(1-.30) = .21Finite population adjustmentNoStandard error of the proportion.10/1.96 = .051Sample size.21/ (.051)2 = 81Appendix 14a: Key Terms Central limit theoremConfidence intervalConfidence levelInterval estimatePoint estimateProportionDetermining Sample SizeAppendix 14aMcGraw-Hill/IrwinCopyright © 2014 by The McGraw-Hill Companies, Inc. All rights reserved.Photo AttributionsSlideSource10©Chris Whitehead/cultura/Corbis12Verdina Anna/Getty Images