Dunnett's Test - Real Statistics Using Excel

Dunnett's test is used when we want to compare one group (usually the control treatment) with the other groups. · The test is similar to Tukey's HSD, except that ... Skiptocontent Menu Dunnett’stestisusedwhenwewanttocompareonegroup(usuallythecontroltreatment)withtheothergroups.Inthiscase,Dunnett’stestismorepowerfulthantheotherANOVApost-hoctestsdescribedonthiswebsite. ThetestissimilartoTukey’sHSD,exceptthatinsteadoftesting wetestwhether wheren=sizeofthegroupsamples, x̄o =meanofthecontrolgroup, x̄j isthemeanofanyothergroupandtdisthe(two-tailed)Dunnett’scriticalvaluegivenintheDunnett’sTable.Thetablecontainsthevaluestd(k,dfW,α) wherek =thenumberofgroups(treatments)includingthecontrol. Thetestcanalsobeusedwhenthegroupmeansarenotequalvia although,sinceDunnett’sTable isbasedonequalgroupsizes,theaboveformulaisonlyaccurateifthegroupsizesarenottoodifferent. RealStatisticsFunction:ThefollowingfunctionisprovidedintheRealStatisticsResourcePack: DCRIT(k,df,α,interp)=thecriticalvaluetdforkindependentvariables,thegivendegreesoffreedomandvalueofalpha. Ifinterp=TRUE(default)therecommendedinterpolationisused;otherwiselinearinterpolationisused. DPROB(x,k,df,iter,interp,txt)=estimatedp-valueforthe Dunnett’stestatxforthedistributionwith kgroups,degreesoffreedomdf,iter=#ofiterationsinestimatingthep-valuefromtheDunnett’stableofcriticalvalues(default=40)andinterp=TRUE(default)forrecommendedinterpolationandFALSE(linearinterpolation). Notethatwhentxt=FALSE(default)ifthep-valueislessthan.01,DPROBisroundeddownto0,whileifthep-valueisgreaterthan.1itisroundedupto1.Whentxt=TRUE,thentheoutputtakestheform“<.01>.1”. RealStatisticsDataAnalysisTool:WenowshowhowtousetheDunnett’sTestdataanalysistooltoaddressExample1. Example1:AssumingthatMethod1isthecontrolgroupinExample2ofANOVABasicConcepts,comparethemeanofthismethodwiththemeansoftheothermethodsusingDunnett’stest.ThedataisrepeatedinFigure1. WecanperformthistestusingtheSingleFactorANOVAtool.WhenthedialogboxshowninFigure1ofANOVAAnalysisToolappears,fillintheInputRangewithA3:D11,makesurethattheColumnheadingsincludedwithdataischeckedandchoosetheDunnett’soption.AfterclickingontheOKbutton,theoutputshownontherightsideofFigure1isdisplayed. Figure1–Dunnett’sTest WeseethatthereisasignificantdifferencebetweenMethod1(thecontrol)and2aswellasbetweenMethod1andMethod3. NotethatcellI11containstheformula=DCRIT(COUNT(I4:I7),H11,L2).ThusthecriticalvalueinDunnett’sTable whenk=4,df=28andα=.05is2.483. RealStatisticsResources Follow@Real1Statistics Search Searchfor: One-wayAnalysisofVariance(ANOVA) BasicConceptsforANOVA ANOVAAnalysisToolandConfidenceIntervals Experiment-wiseerrorrate PlannedComparisons UnplannedComparisons TukeyHSD(HonestlySignificantDifference) Tukey-KramerTest Games-HowellTest REGWQPost-hocTest Dunnett’sTest Hsu’sMCB ScheffeTest PairwisetTestsafterANOVA TrendAnalysisusingPolynomialContrastCoefficients AssumptionsforANOVA HomogeneityofVariances OutliersinANOVA EffectSizeforANOVA PowerforOne-wayANOVA EstimatingNoncentralityParameterforANOVA ConfidenceIntervalsforANOVAPowerandEffectSize PowerofTukeyHSDTest Kruskal-WallisTest Nominal-OrdinalChi-squareTest Jonckheere–TerpstreTest Welch’sANOVATest Brown-ForsytheF*Test Mood’sMedianTest HomogeneityofCoefficientsofVariation ResamplingforANOVA CharlesZaiontz CloseHome FreeDownload ResourcePack ExamplesWorkbooks QATAccess Donation(Optional) Basics Introduction ExcelEnvironment RealStatisticsEnvironment ProbabilityFunctions DescriptiveStatistics HypothesisTesting GeneralPropertiesofDistributions Distributions NormalDistribution SamplingDistributions BinomialandRelatedDistributions StudentstDistribution Chi-squareandFDistributions OtherKeyDistributions DistributionFitting OrderStatistics TestingforNormalityandSymmetry ANOVA One-wayANOVA FactorialANOVA ANOVAwithRandomorNestedFactors DesignofExperiments ANOVAwithRepeatedMeasures AnalysisofCovariance(ANCOVA) Miscellaneous Correlation Reliability Non-parametricTests TimeSeriesAnalysis PanelDataModels SurvivalAnalysis BayesianStatistics WinningatWordle HandlingMissingData Regression LinearRegression MultipleRegression LogisticRegression MultinomialRegression OrdinalRegression PoissonRegression Log-linearRegression Multivariate DescriptiveMultivariateStatistics MultivariateNormalDistribution HotellingT-square MANOVA RepeatedMeasuresTests BoxTest FactorAnalysis ClusterAnalysis DiscriminantAnalysis CorrespondenceAnalysis Appendix FAQs MathematicalNotation ExcelCapabilities MatricesandIterativeProcedures LinearAlgebraandAdvancedMatrixTopics OtherMathematicalTopics StatisticsTables Bibliography Author Citation Blogs Tools RealStatFunctionInfo DistributionFunctions Non-ParametricTestFunctions DescriptiveStatsandReformattingFunctions RegressionandANOVAFunctions Correlation/ReliabilityFunctions MultivariateFunctions TimeSeriesFunctions MissingDataFunctions MathematicalFunctions DataAnalysisTools YouTubeVideos ContactUs Search Searchfor: