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TrimSize:170mmx244mm Barton ffirs.tex V2-07/22/2014 12:36A.M. Pageii TrimSize:170mmx244mm Barton ffirs.tex V2-07/22/2014 12:36A.M. Pagei Medical Statistics A Guide to SPSS, Data Analysis and Critical Appraisal TrimSize:170mmx244mm Barton ffirs.tex V2-07/22/2014 12:36A.M. Pageii TrimSize:170mmx244mm Barton ffirs.tex V2-07/22/2014 12:36A.M. Pageiii Medical Statistics A Guide to SPSS, Data Analysis and Critical Appraisal Second Edition Belinda Barton Children’sHospitalEducationResearchInstitute,TheChildren’sHospitalatWestmead, Sydney,Australia Jennifer Peat HonoraryProfessor,AustralianCatholicUniversityandResearchConsultant, Sydney,Australia TrimSize:170mmx244mm Barton ffirs.tex V2-07/22/2014 12:36A.M. Pageiv Thiseditionfirstpublished2014©2014byJohnWiley&SonsLtd. BMJBooksisanimprintofBMJPublishingGroupLimited,usedunderlicencebyJohnWiley&Sons. Firstedition©2005byBlackwellPublishingLtd. 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[DNLM:1.StatisticsasTopic–methods.2.ResearchDesign.WA950] R853.S7 610.285’555–dc23 2014020556 AcataloguerecordforthisbookisavailablefromtheBritishLibrary. Wileyalsopublishesitsbooksinavarietyofelectronicformats.Somecontentthatappearsinprintmaynot beavailableinelectronicbooks. Typesetin9.5/12ptMeridien&FrutigerbyLaserwordsPrivateLimited,Chennai,India 1 2014 TrimSize:170mmx244mm Barton ftoc.tex V2-07/22/2014 12:37A.M. Pagev Contents Introduction,ix Acknowledgements,xiii Aboutthecompanionwebsite,xv Chapter1 CreatinganSPSSdatafileandpreparingtoanalysethedata,1 1.1 CreatinganSPSSdatafile,1 1.2 OpeningdatafromExcelinSPSS,6 1.3 Categoricalandcontinuousvariables,7 1.4 Classifyingvariablesforanalyses,7 1.5 HypothesistestingandPvalues,8 1.6 Choosingthecorrectstatisticaltest,9 1.7 Samplesizerequirements,10 1.8 Studyhandbookanddataanalysisplan,12 1.9 Documentation,13 1.10 Checkingthedata,13 1.11 Avoidingandreplacingmissingvalues,14 1.12 SPSSdatamanagementcapabilities,16 1.13 ManagingSPSSoutput,20 1.14 SPSShelpcommands,21 1.15 Goldenrulesforreportingnumbers,21 1.16 Notesforcriticalappraisal,21 References,23 Chapter2 Descriptivestatistics,24 2.1 Parametricandnon-parametricstatistics,25 2.2 Normaldistribution,25 2.3 Skeweddistributions,26 2.4 Checkingfornormality,29 2.5 Transformingskewedvariables,43 2.6 Dataanalysispathway,49 2.7 Reportingdescriptivestatistics,49 2.8 Checkingfornormalityinpublishedresults,50 2.9 Notesforcriticalappraisal,51 References,51 Chapter3 Comparingtwoindependentsamples,52 3.1 Comparingthemeansoftwoindependentsamples,52 3.2 One-andtwo-sidedtestsofsignificance,54 3.3 Effectsizes,55 3.4 Studydesign,57 3.5 Influenceofsamplesize,58 3.6 Two-samplet-test,71 v TrimSize:170mmx244mm Barton ftoc.tex V2-07/22/2014 12:37A.M. Pagevi vi Contents 3.7 Confidenceintervals,73 3.8 Reportingtheresultsfromtwo-samplet-tests,75 3.9 Rank-basednon-parametrictests,80 3.10 Notesforcriticalappraisal,88 References,89 Chapter4 Pairedandone-samplet-tests,90 4.1 Pairedt-tests,90 4.2 Non-parametrictestforpaireddata,97 4.3 Standardizingfordifferencesinbaselinemeasurements,99 4.4 Single-samplet-test,102 4.5 Testingforabetween-groupdifference,106 4.6 Notesforcriticalappraisal,110 References,111 Chapter5 Analysisofvariance,112 5.1 BuildingANOVAandANCOVAmodels,113 5.2 ANOVAmodels,113 5.3 One-wayanalysisofvariance,117 5.4 EffectsizeforANOVA,127 5.5 Post-hoctestsforANOVA,128 5.6 Testingforatrend,133 5.7 Reportingtheresultsofaone-wayANOVA,134 5.8 FactorialANOVAmodels,135 5.9 Anexampleofathree-wayANOVA,140 5.10 Analysisofcovariance(ANCOVA),145 5.11 TestingthemodelassumptionsofANOVA/ANCOVA,149 5.12 ReportingtheresultsofanANCOVA,158 5.13 Notesforcriticalappraisal,158 References,160 Chapter6 Analysesoflongitudinaldata,161 6.1 Studydesign,161 6.2 Samplesizeandpower,162 6.3 Covariates,163 6.4 AssumptionsofrepeatedmeasuresANOVAandmixed models,163 6.5 Repeatedmeasuresanalysisofvariance,164 6.6 Linearmixedmodels,182 6.7 Notesforcriticalappraisal,195 References,196 Chapter7 Correlationandregression,197 7.1 Correlationcoefficients,197 7.2 Regressionmodels,205 7.3 Multiplelinearregression,213 7.4 Interactions,230 TrimSize:170mmx244mm Barton ftoc.tex V2-07/22/2014 12:37A.M. Pagevii Contents vii 7.5 Residuals,235 7.6 Outliersandremotepoints,237 7.7 Validatingthemodel,240 7.8 Reportingamultiplelinearregression,241 7.9 Non-linearregression,242 7.10 Centering,244 7.11 Notesforcriticalappraisal,247 References,247 Chapter8 Ratesandproportions,249 8.1 Summarizingcategoricalvariables,249 8.2 Describingbaselinecharacteristics,251 8.3 Incidenceandprevalence,252 8.4 Chi-squaretests,253 8.5 2×3Chi-squaretables,260 8.6 Cellswithsmallnumbers,262 8.7 Exactchisquaretest,263 8.8 Numberofcellsthatcanbetested,264 8.9 Reportingchi-squaretestsandproportions,266 8.10 Largecontingencytables,267 8.11 Categorizingcontinuousvariables,271 8.12 Chi-squaretrendtestfororderedvariables,273 8.13 Numberneededtotreat(NNT),277 8.14 Pairedcategoricalvariables:McNemar’schi-squaretest,281 8.15 Notesforcriticalappraisal,285 References,286 Chapter9 Riskstatistics,287 9.1 Riskstatistics,287 9.2 Studydesign,288 9.3 Oddsratio,288 9.4 Protectiveoddsratios,296 9.5 Adjustedoddsratios,298 9.6 Relativerisk,308 9.7 Numberneededtobeexposedforoneadditionalpersonto beharmed(NNEH),312 9.8 Notesforcriticalappraisal,312 References,313 Chapter10 Testsofreliabilityandagreement,314 10.1 Reliabilityandagreement,314 10.2 Kappastatistic,317 10.3 Reliabilityofcontinuousmeasurements,321 10.4 Intra-classcorrelation,322 10.5 Measuresofagreement,325 10.6 Notesforcriticalappraisal,329 References,329 TrimSize:170mmx244mm Barton ftoc.tex V2-07/22/2014 12:37A.M. Pageviii viii Contents Chapter11 Diagnosticstatistics,331 11.1 Codingfordiagnosticstatistics,331 11.2 Positiveandnegativepredictivevalues,332 11.3 Sensitivityandspecificity,335 11.4 Likelihoodratio,338 11.5 ReceiverOperatingCharacteristic(ROC)Curves,339 11.6 Notesforcriticalappraisal,348 References,349 Chapter12 Survivalanalyses,350 12.1 Studydesign,351 12.2 Censoredobservations,351 12.3 Kaplan–Meiersurvivalmethod,351 12.4 Coxregression,360 12.5 Questionsforcriticalappraisal,368 References,368 Glossary,370 Usefulwebsites,381 Index,385