Essentials of Medical Statistics

512 Pages·2001·2.24 MB·english

by  Kirkwood

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Essential Medical Statistics
Dedication
To our children:
Daisyand SamKirkwood
Max, Kittyand Emily Sterne
SECOND EDITION
Essential
Medical
Statistics
Betty R. Kirkwood
MAMScDIC,HonMFPHM,FMedSci
ProfessorofEpidemiologyandInternationalHealth
LondonSchoolofHygieneandTropicalMedicine
UniversityofLondon
AQ1
Jonathan A.C. Sterne
MAMScPhD
ProfessorofMedicalStatisticsandEpidemiology
DepartmentofSocialMedicine
UniversityofBristol
#1988,2003byBlackwellScienceLtd
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Firstpublished1988
Secondedition2003
2 2006
LibraryofCongressCataloging-in-PublicationData
Kirkwood,BettyR.
Essentialmedicalstatistics/BettyR.Kirkwood,
JonathanA.C.Sterne.—2nded.
p.;cm.
Rev.ed.of:Essentialsofmedicalstatistics/BettyR.Kirkwood.1988.
Includesbibliographicalreferencesandindex.
ISBN0–86542–871–9
1. Medicine–Research–Statisticalmethods.2. Medicalstatistics.
[DNLM:1.Statistics.2.Biometry.WA950K59e2003]
I.Sterne,JonathanA.C.II.Kirkwood,BettyR.Essential
medicalstatistics.III.Title.
R853.S7K4972003
6100.7027—dc21
2002015537
ISBN:978–0–86542–871–3
AcataloguerecordforthistitleisavailablefromtheBritishLibrary
BSL:
Setin10/13ptTimesbyKolamInformationServicesPvt.Ltd,Pondicherry,India
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Contents
Prefacetothesecondedition vii Part C: Analysisof binary outcomes
Prefacetothefirstedition ix 14 Probability,riskandodds
(ofdisease) 131
15 Proportionsandthebinomial
Part A: Basics
distribution 138
1 Usingthisbook 3
16 Comparingtwoproportions 148
2 Definingthedata 9
17 Chi-squaredtestsfor2(cid:2)2andlarger
3 Displayingthedata 15 contingencytables 165
18 Controllingforconfounding:
stratification 177
Part B: Analysisof numerical outcomes
19 Logisticregression:comparingtwoor
4 Means,standarddeviations
moreexposuregroups 189
andstandarderrors 33
20 Logisticregression:controllingfor
5 Thenormaldistribution 42
confoundingandotherextensions 205
6 Confidenceintervalforamean 50
21 Matchedstudies 214
7 Comparisonoftwomeans:
confidenceintervals,hypothesis
testsandP-values 58 PartD:Longitudinalstudies:Analysisof
rates and survival times
8 UsingP-valuesandconfidenceintervals
tointerprettheresultsofstatistical 22 Longitudinalstudies,ratesandthe
analyses 71 Poissondistribution 227
9 Comparisonofmeansfromseveral 23 Comparingrates 240
groups:analysisofvariance 80
24 Poissonregression 249
10 Linearregressionandcorrelation 87
25 Standardization 263
11 Multipleregression 98
26 Survivalanalysis:displayingand
12 Goodnessoffitandregression comparingsurvivalpatterns 272
diagnostics 107
27 Regressionanalysisofsurvival
13 Transformations 118 data 287
vi Contents
Part E: Statistical modelling Appendix: Statistical tables
28 Likelihood 297 A1 Areasintailofthestandardnormal
distribution 470
29 Regressionmodelling 315
A2 Percentagepointsofthestandard
30 Relaxingmodelassumptions 343
normaldistribution 472
31 Analysisofclustereddata 355
A3 Percentage pointsofthet
32 Systematicreviewsand distribution 473
meta-analysis 371
A4 Two-sidedP-valuesforthet
33 Bayesianstatistics 388 distribution,accordingtothevalue
oftheteststatistic 474
A5 Percentagepointsofthe(cid:2)2
Part F:Studydesign, analysis distribution 476
andinterpretation
A6 Probits 477
34 Linkinganalysistostudydesign:
A7 CriticalvaluesfortheWilcoxon
summaryofmethods 395
matchedpairssignedranktest 479
35 Calculationofrequiredsample
A8 CriticalrangesfortheWilcoxonrank
size 413
sumtest 480
BSL:
36 Measurementerror:assessmentand
A9 Randomnumbers 482 check
implications 429
and
37 Measuresofassociationand complete
Bibliography 487
impact 447 Pg.nos
Index 493
38 Strategiesforanalysis 458
Preface to the second edition
The practice of medical statistics has changed considerably since the first edition
waswritten.Atthattimetheageofthepersonalcomputerwasjustbeginning,and
serious statistical analyses were conducted by specialist statisticians using main-
frame computers. Now, there is ready access to statistical computing—even the
most sophisticated statistical analyses can be done using a personal computer.
This has been accompanied by the growth of the evidence-based medicine move-
ment and a commitment of medical journals to improve the statistical rigour of
papers they publish.
These changes mean that the boundary between what used to be considered
‘basic’ or ‘essential’ statistics and more advanced methods has been blurred.
Astatisticalanalysispresentedinaleadinggeneralmedicaljournalismorelikely
to use logistic regression (formerly considered a specialist technique) than to
present results from (cid:2)2 tests. In this second edition we describe the most com-
monly used regression models—multiple linear regression, logistic regression,
Poisson regression and Cox regression—and explain how these include many
basic methods as special cases. By including chapters on general issues in regres-
sion modelling, interpretation of analyses and likelihood, we aim to present a
unifiedviewofmedicalstatisticsandstatisticalinference,andtoreflecttheshiftin
emphasisinmodernmedicalstatisticsfromhypothesistestingtoestimation.Other
new chapters introduce methods, some relatively new, that allow common prob-
lemsinstatisticalanalysistobeaddressed;theseincludemeta-analysis,bootstrap-
ping, robuststandard errors,and analysis of clustered data.
Our aim throughout has been to retain the strengths of the first edition, by
keeping the emphasis on enabling the reader to know which method to apply
when.Wehavethereforestructuredthebookintopartsrelatingtotheanalysisof
differenttypesofoutcomevariable,andincludednewchaptersonlinkinganalysis
to study design, measures of association and impact, and general strategies for
analysis.
Anumberofthelargerdatasetsusedinthechaptersonregressionmodellingare
available for downloading from the book’s website (www.blackwellpublishing.
com/essentialmedstats), to allow readers to reproduce the analyses presented or
tryoutfurtheranalysesforthemselves.Readersarealsoinvitedtovisitthewebsite
to check forcorrections and updates and togivefeedback, which we welcome.
viii Prefacetothesecondedition
Inwritingthissecondedition,wehavebenefitedfromadviceandsupportfrom
many colleagues, students and friends. In particular, we would like to thank the
manyreaderswhogavefeedbackonthefirsteditionandinspiredustoembarkon
this,CesarVictora,KateTillingandSimonCousensforsowillinglycommenting
onearlydraftsindetail,DavidClaytonandMichaelHillsforgenerousadviceand
unstintinghelponmanyoccasions,GeorgeDaveySmithforhelpfulcommentson
a number of draft chapters and the late Paul Arthur for his enduring encourage-
mentandadvice.WewouldliketoexpressourappreciationtoChristopherBaum,
James Carpenter, Matthias Egger, Stephen Frankel, David Gunnell, Richard
Hayes, Sharon Huttly, Mike Kenward, Peter McCarron, Roger Newson, Steven
Oliver,AndrewPolmear,BiancadeStavola,andLesleyWoodforhelpfuldiscus-
sionsandforsharingtheirinsightsintostatisticalissues.WearegratefultoJames
Carpenter,ErikChristensen,ShahEbrahim,AlisonElliot,RichardHayes,David
Kessler, Carl-Johan Lamm, Debbie Lawlor, Steven Oliver, Mary Penny, Seif
Shaheen and Bianca de Stavola, who generously provided datasets for use as
examples. We would also like to thank Maggie Rae and Alan Haworth, whose
generoushospitalityfacilitatedmuchwriting,andlastbutnotleastHarrietAston,
Emily,KittyandMaxSterne,AlexKhot,andSamandDaisyKirkwood,fortheir
supportand the difference theymakein our lives.
Betty Kirkwood
Jonathan Sterne