choosing a statistical test
TRANSCRIPT
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How to choose a statistical test?Dr. S. A. Rizwan, M.D.
PublicHealthSpecialistSBCM, JointProgram– Riyadh
MinistryofHealth,KingdomofSaudiArabia
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Learningobjectives
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Namethevariouscommonlyusedstatisticaltests• Describethepreconditionstoselectastatisticaltest• Applythecorrecttestfortheproblemathand• Interprettheconclusionsofthetestappropriately
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Introduction
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Weapplyastatisticaltesttoconfirmifourstudyresultshavearisenduetochanceorduetoatrueeffect
• Itisimportanttoapplythecorrecttestforavalidconclusion
• Anumberofconsiderationsarerequiredbeforeselectingatest
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Introduction
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Therearemorethan100sofstatisticaltestsavailable
• Thisbookisausefulandsimpleguide
• Apartfromteststherearemanystatisticalmethodswhicharealsoconsideredstatisticaltests
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Prerequisitesfordecidingatest
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Howmanyvariablesarethere?
• Whatisthenatureofdependentandindependentvariable?
• Howmanycategoriesarethereinthecategoricalvariable?
• Doesthecontinuousvariablefollownormaldistribution? (Parametricvs.Nonparametric)
• Isthereanypairing inthedata/variables?*Recalltypesofvariable/data?
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Whatismeantbydatafollowsnormaldist?
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Asageneralrule• Smallsamples(<30)arenotnormal• Converselylarge(>30)samplesareconsideredto
benormal
• Normaldistributioncanbechecked• Informally:• Visualmethods:histogram,P-P,Q-Qplots• ComparingSDandmean
• Formally:• Statisticaltests(Kolmogorov–Smirnov,Shapiro–
Wilk)
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Dependent/independentvariable?
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
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Dependent/independentvariable?
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Height• Weight• Diet• Socio-economicstatus• Drugtype• Musclemass• Qualityoflife• Wealth• Employment• Sex• Treatmenttype
• Curerate• Survivalindex• Maternalmortalityrate• Teenagepregnancy• Immunisationcoverage• Education• Housetype• Healthaccessibility• Mortality• Tobaccouse• Domesticviolence
*Canyouclassifythesevariablesintodependentandindependent?
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Paired/unpaireddata?
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Paireddata/samplesinwhichnaturalormatchedcouplingsoccur
• Pre-test/post-testsamples• Cross-overtrials• Matchedsamples• Clustersamples
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Howtochooseastatisticaltest?
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
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Onesampletests
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Onedependentvariablecomparedtoahypothesizedpopulation value
• Therearenoindependent variables
• Rarelyusedincommunitymedicine
Natureofvariable Testname
Normal Onesamplet-test
Ordinal/interval Onesamplemedian
Categorical(2levels) Binomialtest
Categorical(>2levels) Chi-squareGOF
*Ifthesamplesizeislargeandwithinknownpopulationparameters,Ztestisused.
Noindependentvariable
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Comparisonof2variables- 1
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Oneindependentvariable• Categorical• Independent• 2levels
• Onedependentvariable
• Someofthemostcommonlyusedtests
• Aka,bivariateanalysis
NatureofDV Testname
Normal Independent samplet-test
Ordinal/interval(notnormal)
Wilcoxon-MannWhitneytest
Categorical(assumptionsmet) Chi-squaretest
Categorical(assumptionsNOTmet) Fisher’sexacttest
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Comparisonof2variables- 2
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Oneindependentvariable• Categorical• Independent• >2levels
• Onedependentvariable
• Someofthemostcommonlyusedtests
• Aka,bivariateanalysis
NatureofDV Testname
Normal OnewayANOVA
Ordinal/interval(notnormal) KruskalWallis
Categorical(assumptionsmet) Chi-squaretest
Categorical(assumptionsNOTmet) Fisher’sexacttest
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Comparisonof2variables- 3
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Oneindependentvariable• Categorical• Dependent• 2levels
• Onedependentvariable
NatureofDV Testname
Normal Pairedt-test
Ordinal/interval(notnormal)
Wilcoxonsignedrankstest
Categorical McNemar
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Comparisonof2variables- 4
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Oneindependentvariable• Categorical• Dependent• >2levels
• Onedependentvariable
NatureofDV Testname
Normal One-wayrepeatedmeasuresANOVA
Ordinal/interval(notnormal) Friedmantest
Categorical Repeatedmeasureslogisticregression
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Comparisonof2variables- 5
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Oneindependentvariable• Interval
• Onedependentvariable
NatureofDV Testname
Normal CorrelationRegression
Ordinal/interval(notnormal)
Non-parametriccorrelation
Categorical Simplelogisticregression
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Otherstatisticalmethods- 1
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Oneormoreindependentvariables• Intervalorcategorical
• Onedependentvariable
NatureofDV Testname
IntervalandNormal MultipleregressionANCOVA
Categorical
MultiplelogisticregressionDiscriminantanalysis
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Otherstatisticalmethods- 2
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Oneindependentvariable• Independentgroups• 2ormorelevels
• 2ormoredependentvariables
NatureofDV Testname
IntervalandNormal OnewayMANOVA
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Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• 2ormoreindependentvariables• Categorical• Independent
• Onedependentvariable
• Someofthemostcommonlyusedtests
• Aka,bivariateanalysis
NatureofDV Testname
Normal FactorialANOVA
Ordinal/interval(notnormal)
Orderedlogisticregression
Categorical Factoriallogisticregression
Otherstatisticalmethods- 3
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Otherstatisticalmethods- 4
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• 2ormoreindependentvariables
• 2ormoredependentvariables
NatureofDV Testname
IntervalandNormalMultivariatemultiplelinearregression
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Otherstatisticalmethods- 5
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• 2ormoredependentvariables NatureofDV Testname
IntervalandNormalCanonicalcorrelationFactoranalysis
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Summary– Testsyoumustknow
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
Typeofbivariatecomparison
Numberofgroups
Independentsamples Pairedsamples
Parametric(normaldistribution)
Non-parametric(non-normaldistribution)
Parametric(normaldistribution)
Non-parametric(non-normaldistribution)
Categoricalvs.categorical
(eg.Treatment typevs.gender)
2
- Chisquaretest(orFishersexacttest) - McNemar test
Categoricalvs.categorical
(eg.Diseaseseverityvs.religion)
>2
- Chisquaretest(orFishersexacttest) - -
Categoricalvs.quantitative
(eg.Twotreatmenttypesvs.meanBP)
2
Studentsttest Wilcoxonranksumtest Pairedttest Wilcoxonsignranktest
Categoricalvs.quantitative
(eg.Threetreatment typevs.meanBP)
>2One-wayANOVA(analysis
ofvariance) KruskalWallistest RepeatedmeasuresANOVA Freidman’stest
Quantitativevs.quantitative
(eg. Agevs.weight)
- Pearson’scorrelation
Regressionanalysis
Spearman’srankcorrelation Generalizedlinearmodels -
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Summary
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
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Takehomemessages
Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh
• Anumberofthingsmustbeconsideredbeforeselectingatest
• Foragiventesttheassumptionsmustbesatisfied
• Theresultsmustbeinterpretedcautiouslywiththecontext