Essential Epidemiology: An Introduction for Students and Health Professionals, 2nd Edition (Essential Medical Texts for Students and Trainees)

461 Pages·2011·5.93 MB·English

by  Penny Webb

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EssentialEpidemiology
AnIntroductionforStudentsandHealthProfessionals
SecondEdition
PennyWebb,MA(Cambridge),DPhil(Oxford),isaSeniorResearchFellowatthe
QueenslandInstituteofMedicalResearchandAssociateProfessorintheSchool
ofPopulationHealth,UniversityofQueensland.Shehasworkedasavisitingsci-
entistattheInternationalAgencyforResearchonCancer,France,andHarvard
University,USAandhaspublishedmorethan120originalresearchpapersinthe
fieldofcancerepidemiology.
Chris Bain,MBBS(UQ),MPH,MSc(Harvard)isReaderinEpidemiologyinthe
School of Population Health, University of Queensland. He has been teaching
epidemiologytopublichealthandmedicalstudentsforover3decadesandhas
co-authoredabookonhowtoconductasystematicreviewaswellasmorethan
100 original epidemiology research papers. He has worked at Harvard in the
USAandasavisitingresearcherattheLondonSchoolofHygieneandTropical
MedicineandattheUniversitiesofCambridge,OxfordandBristolintheUK.

Essential
Epidemiology
An Introduction for Students
and Health Professionals
Second Edition
Penny Webb
SeniorResearchFellowandHead,
GynaecologicalCancersGroup,
QueenslandInstituteofMedicalResearch,
Brisbane,Australia
and
Chris Bain
ReaderinEpidemiology,
SchoolofPopulationHealth,
UniversityofQueensland,
Brisbane,Australia
cambridgeuniversitypress
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Informationonthistitle:www.cambridge.org/9780521177313
(cid:2)C P.WebbandC.Bain2011
Thispublicationisincopyright.Subjecttostatutoryexception
andtotheprovisionsofrelevantcollectivelicensingagreements,
noreproductionofanypartmaytakeplacewithoutthewritten
permissionofCambridgeUniversityPress.
Firstpublished2011
PrintedintheUnitedKingdomattheUniversityPress,Cambridge
AcataloguerecordforthispublicationisavailablefromtheBritishLibrary
LibraryofCongressCataloguinginPublicationdata
Webb,Penny,1963–
Essentialepidemiology:anintroductionforstudentsandhealthprofessionals/
PennyWebbandChrisBain.–2nded.
p. ; cm.
Includesbibliographicalreferencesandindex.
ISBN978-0-521-17731-3(pbk.)
1.Epidemiology. I.Bain,Chris,1947– II.Title.
[DNLM: 1.EpidemiologicMethods. 2.Epidemiology. WA105]
RA651.W385 2011
614.4–dc22 2010040293
ISBN978-0-521-17731-3Paperback
Additionalresourcesforthispublicationatwww.cambridge.org/webb

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informationwhichisinaccordwithacceptedstandardsandpracticeatthetimeof
publication.Althoughcasehistoriesaredrawnfromactualcases,everyefforthasbeen
madetodisguisetheidentitiesoftheindividualsinvolved.Nevertheless,theauthors,
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totallyfreefromerror,notleastbecauseclinicalstandardsareconstantlychanging
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Contents
Foreword x
Preface xi
1 Epidemiologyis... 1
Acaseoffoodpoisoning 3
Subdisciplinesofepidemiology 4
Onepidemics 6
Anhistoricalepidemic 8
Thebeginnings 9
Whatdoesepidemiologyoffer? 17
Whatdoepidemiologistsdo? 18
Anaturalexperiment 24
Conclusions 24
References 27
2 Howlongisapieceofstring?Measuringdiseasefrequency 29
Whatarewemeasuring? 30
Theconcepts:prevalenceandincidence 32
Measuringdiseaseoccurrenceinpractice:epidemiologicalstudies 38
Measuringdiseaseoccurrencein practice:usingroutinedata 45
Othermeasurescommonlyusedinpublichealth 52
Measuringthe‘burdenofdisease’ 59
Summary 68
Questions 68
References 69
3 Who,what,whereandwhen?Descriptiveepidemiology 71
Casereportsandcaseseries 72
Prevalencesurveys 74
Routinedatacollections 76
Sourcesofsummarydata 83
Creativeuseofexistingdata 87
v
vi Contents
Confidentiality 92
Summary 92
References 92
4 Healthyresearch:studydesignsforpublichealth 94
Observationalstudies 96
Interventionstudies 112
Awordaboutethics 117
Summary 121
Questions 121
References 122
5 Why?Linkingexposureanddisease 125
Lookingforassociations 126
Ratiomeasures(relativerisk) 128
Differencemeasures(attributablerisk) 133
Relativeriskversusattributablerisk:anexample 141
Case–controlstudies 143
Summary 149
Questions 149
References 153
6 Headsortails:theroleofchance 154
Randomsamplingerror 154
Confidenceintervals(CI) 156
Statisticsinepidemiology 158
Statisticalversusclinicalsignificance 163
Afinalwordaboutconfidenceintervalsandp-values 165
Summary 165
Questions 165
References 166

7 Allthatglittersisnotgold:theproblemoferror 167
Sourcesoferrorinepidemiologicalstudies 169
Selectionbias 169
Measurementorinformationerror 181
Summary 194
Questions 194
References 196
8 Muddiedwaters:thechallengeofconfounding 197
Anexampleofconfounding:isalcoholariskfactorforlungcancer? 198
Criteriaforaconfounder 201
Theeffectsofconfounding 202
Controlofconfounding 208
Contents vii
Confounding:thebottomline 218
Questions 219
References 220
9 Readingbetweenthelines:readingandwriting 221
epidemiologicalpapers
Theresearchquestionandstudydesign 222
Thestudysample:selectionbias 223
Measuringdiseaseandexposure:measurementbias 226
Confounding 228
Chance 230
Studyvalidity 230
Descriptivestudies 232
Writingpapers 233
Summary:oneswallowdoesn’tmakeasummer 234
Questions 235
References 235
10 Whosanktheboat?Associationandcausation 237
Whatdowemeanbyacause? 238
Associationversuscausation 242
Evaluatingcausation 243
Evaluatingcausalityinpractice:doesH.pylori 250
causestomachcancer?
Andthenwhat? 250
References 251
11 Assemblingthebuildingblocks:reviewsandtheiruses 252
Whatisasystematicreview? 253
Identifyingtheliterature 253
Differenttypesofstudy 256

Summarisingthedata 259
Assessmentofcausality 265
Assessingthequalityofasystematicreview 267
Makingjudgementsinpractice 267
Theendresult 272
Summary 273
References 273
12 Outbreaks,epidemicsandclusters 276
ProfessorAdrianSleigh
NationalCentreforEpidemiologyandPopulationHealth,
AustralianNationalUniversity
Outbreaks,epidemics,endemicsandclusters 278
Rarediseaseclusters 279
viii Contents
Epidemiologyofinfectiousdiseases 282
Acausalmodel 285
Whatinfluencesthespreadofinfectiousdiseases? 286
Epidemicsoroutbreaks 293
Investigatingoutbreaks 295
Epidemicprevention 299
Tuberculosis:acasestudy 300
Conclusion 304
Questions 304
References 305
13 Watchingnotwaiting:surveillanceand 307
epidemiologicalintelligence
Thescopeofsurveillance 309
Typesofsurveillance 312
Surveillanceinpractice 315
Evaluationofsurveillance 321
Summary 321
References 322
14 Prevention:betterthancure? 323
Diseasepreventioninpublichealth 323
Thescopeforpreventivemedicine 328
Strategiesforprevention 331
Thepopulationattributablefractionasaguidetoprevention 336
Preventioninpractice 339
Evaluationofpreventiveinterventionsinpractice 341
Afinal(cautionary)word 342
Question 343
References 343

15 Earlydetection:whatbenefitsatwhatcost? 345
Whyscreen? 346
Therequirementsofascreeningprogramme 349
Evaluationofascreeningprogramme 361
Thenegativeconsequencesofascreeningprogramme 370
Summary 371
Questions 372
References 373
16 Afinalword... 375
Whatdoesthefutureholdforepidemiology? 377
Wheretonow? 382
Afinalword 385
References 386