How to choose a statistical test?Dr. S. A. Rizwan, M.D.

PublicHealthSpecialistSBCM, JointProgram– Riyadh

MinistryofHealth,KingdomofSaudiArabia

Learningobjectives

Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh

• Namethevariouscommonlyusedstatisticaltests• Describethepreconditionstoselectastatisticaltest• Applythecorrecttestfortheproblemathand• Interprettheconclusionsofthetestappropriately

Introduction

Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh

• Weapplyastatisticaltesttoconfirmifourstudyresultshavearisenduetochanceorduetoatrueeffect

• Itisimportanttoapplythecorrecttestforavalidconclusion

• Anumberofconsiderationsarerequiredbeforeselectingatest

Introduction

Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh

• Therearemorethan100sofstatisticaltestsavailable

• Thisbookisausefulandsimpleguide

• Apartfromteststherearemanystatisticalmethodswhicharealsoconsideredstatisticaltests

Prerequisitesfordecidingatest

Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh

• Howmanyvariablesarethere?

• Whatisthenatureofdependentandindependentvariable?

• Howmanycategoriesarethereinthecategoricalvariable?

• Doesthecontinuousvariablefollownormaldistribution? (Parametricvs.Nonparametric)

• Isthereanypairing inthedata/variables?*Recalltypesofvariable/data?

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)

Dependent/independentvariable?

Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh

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?

Paired/unpaireddata?

Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh

• Paireddata/samplesinwhichnaturalormatchedcouplingsoccur

• Pre-test/post-testsamples• Cross-overtrials• Matchedsamples• Clustersamples

Howtochooseastatisticaltest?

Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh

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

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

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

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

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

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

Otherstatisticalmethods- 1

Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh

• Oneormoreindependentvariables• Intervalorcategorical

• Onedependentvariable

NatureofDV Testname

IntervalandNormal MultipleregressionANCOVA

Categorical

MultiplelogisticregressionDiscriminantanalysis

Otherstatisticalmethods- 2

Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh

• Oneindependentvariable• Independentgroups• 2ormorelevels

• 2ormoredependentvariables

NatureofDV Testname

IntervalandNormal OnewayMANOVA

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

Otherstatisticalmethods- 4

Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh

• 2ormoreindependentvariables

• 2ormoredependentvariables

NatureofDV Testname

IntervalandNormalMultivariatemultiplelinearregression

Otherstatisticalmethods- 5

Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh

• 2ormoredependentvariables NatureofDV Testname

IntervalandNormalCanonicalcorrelationFactoranalysis

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 -

Summary

Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh

Takehomemessages

Demystifying statistics! – Lecture 6 SBCM, Joint Program – RiyadhSBCM, Joint Program – Riyadh

• Anumberofthingsmustbeconsideredbeforeselectingatest

• Foragiventesttheassumptionsmustbesatisfied

• Theresultsmustbeinterpretedcautiouslywiththecontext

Thankyou!Emailyourqueriestosarizwan1986@outlook.com