Epidemiologic methods : studying the occurrence of illness

481 Pages·2015·5.718 MB·English

by  Koepsell, Thomas D., Weiss, Noel S

SECOND EDITION
EPIDEMIOLOGIC
METHODS
Studying the Occurrence
of Illness
NOEL S. WEISS
THOMAS D. KOEPSELL
University of Washington
1
3
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Epidemiologicmethods:studyingtheoccurrenceofillness/NoelS.Weiss,ThomasD.Koepsell.—Secondedition.
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ISBN978–0–19–531446–5(alk.paper)
I. Weiss,NoelS.,1941–author. II. Title. III. Title:Epidemiologicmethods.
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EPIDEMIOLOGIC METHODS
CONTENTS
Preface vii 12. ConfoundingandItsControl:
Advanced 225
1. Introduction:AnEpidemicofBlindnessin 13. RandomizedTrials 280
YoungChildren 1 14. CohortStudies 320
2. DiseasesandPopulations 10 15. Case-ControlStudies 340
3. DiseaseFrequency:Basic 27 16. EcologicalandMulti-LevelStudies 360
4. DiseaseFrequency:Advanced 48 17. InductionPeriodsandLatentPeriods 381
5. OverviewofStudyDesigns 76 18. ImprovingtheSensitivityof
6. SourcesofDataonDiseaseOccurrence 105 EpidemiologicStudies 390
7. Person,Place,andTime 128 19. Screening 407
8. InferringaCausalRelationBetween 20. OutbreakInvestigation 428
ExposureandDisease 156 21. EvaluatingtheEffectsof
9. MeasuresofExcessRisk 168 PoliciesonHealth 447
10. MeasurementError 179
Index 463
11. ConfoundingandItsControl:Basic 211

PREFACE
Epidemiologyatanygiventimeissomethingmorethanthetotalofitsestablishedfacts.Itincludestheir
orderlyarrangementintochainsofinferencewhichextendmoreorlessbeyondtheboundsofdirect
observation.Suchofthesechainsasarewellandtrulylaidguideinvestigationtothefactsofthefuture.
—WADEHAMPTONFROST1
Between us, we have accumulated more than 60 research themselves, or who need methodological
person-yearsteachingcoursesontheprinciplesand expertise to interpret and synthesize properly the
methods of epidemiology. We have jointly taught resultsofepidemiologic research producedbyoth-
a two-course sequence at the University of Wash- ers. Itstartsatthebeginning, sotospeak, butcov-
ington since the mid-1980s. During this time, we ersmuchofthematerialinmoredetailthanwould
havelistenedtothereactionsofmanystudentswho be desired by a reader who wished only to have a
werebeingintroducedtothisfield.Onecamefroma general appreciation of epidemiology. Those who
womanwhosaidshederivedanalmostestheticplea- have already taken an introductory course in epi-
sure from epidemiology: she found bothefficiency demiologymayfindhereawelcomereviewofbasic
andbeautyintheprocessoftakingrawobservations concepts,aswellasnew,moreadvancedmaterial.
ontheoccurrenceofanillnessinhumansandweav- A brief outline of the book may be helpful.
ingtheminto“chainsofinferences”aboutthecauses Chapter1tellsthestoryofarealdiseaseoutbreak,
ofthatillness,whichoftenhadthepotentialtolead introducing epidemiologic concepts and designs
toprevention. alongthewaythatwillbecoveredindepthinlater
We suspect that not too many of our students chapters.Chapter2setsforthanepidemiologicview
wouldhaveusedthewordesthetictodescribeanyof of diseases and populations, leading into Chapters
their feelings about our course, even their positive 3and4,onmeasuringdiseasefrequencyinpopula-
feelings.(Somemighthavesaidthatanestheticbetter tions.Chapter5paintsthe“bigpicture”ofresearch
characterizedsomeoftheclasssessions!) Nonethe- designs in epidemiology, so that their names are
less,weliketothinkthatthefirststudenthadinter- familiarwhenusedinchaptersthatfollow.Chapters
nalized what we were trying to convey—that the 6and7highlightseveralspecificsourcesofnumera-
techniquesofstructuringobservationsandanalyzing toranddenominatordatainepidemiologyandpro-
theinformationgathered(uponwhichsomuchtime videexamplesoftheperson/place/timeconceptual
and effort are expended in class) are tobeused to frameworkthatunderliesmanydescriptiveepidemi-
produce“...chains[that]arewellandtrulylaid...” ologicstudies.
inthehopeofguiding“investigationtothefactsof As a transition into analytic epidemiology,
the future.” Having produced extensive classroom Chapter8discussesthekindsofepidemiologicevi-
materialstoachieveourgoals,wefeltthatwithalittle dencethatbearonaninferencethatanassociation
(!)extralaborwecouldorganizethesematerialsinto may be causal. Chapter 9 also focuses on associ-
abookforotherstudentsofepidemiology. ations, describing several quantitative measures of
Whichstudents? Thebookisaimedatbeginning excess risk that can be calculated from epidemio-
and intermediate students of epidemiologic meth- logic data. Chapter 10 introduces several quantita-
ods. It is meant to serve as an introduction to the tivetechniquesforassessingthereliabilityandvalid-
fieldforpeoplewhointendtoconductepidemiologic ity of epidemiologic measurements and describes
1Fromhisintroductionto:SnowJ.SnowonCholera.
NewYork:TheCommonwealthFund,1936.
viii PREFACE
how measurement error affects observed associa- the applicability of the principles and methods to
tions. Chapter 11 describes what confounding is, real-lifesituations.
how it is traditionally assessed, and basic methods From the beginning, thebook hasbeen ajoint
foritscontrol.Chapter12(newinthisedition)dis- enterprisebythetwoofus.Eachofusdraftedabout
cussesmoreadvancedaspectsofconfounding:alter- halfofthechapters.Noelwasleadauthoronchapters
native conceptualizations, causal diagrams, multi- 8–9,11,14–15,and17–18;Tomwasleadauthoron
variableanalysis,data-reductionapproaches,inverse chapters1–7,12–13,16,and21.Chapters10and19
probability–weighting, instrumental variables, and wereco-authoredbybothofus.Eachofuswasthe
time-dependentconfounding. primarycriticalrevieweroftheother’sdraftchapters,
Chapters 13–16each focus in depth on a class andbothofusarepreparedtostandbythebookas
of epidemiologic study designs: randomized trials, awhole.JenniferLloydandJeffreyDuchin,epidemi-
cohortstudies,case-controlstudies,andecologicand ologistswithPublicHealthSeattleandKingCounty,
multi-levelstudies.Chapter17discussestheimplica- contributed the chapter on outbreak investigation,
tionsforepidemiologicstudiesofthetemporalrela- forwhichwearegrateful.
tionshipbetweenexposureandoutcome.Chapter18 Therebeingnobetterwayofdecidingtheorder
describeswaysinwhichepidemiologicstudiescanbe ofournamesontheentirebook,weagreedtoalter-
designedandanalyzedtoenhancethelikelihoodthat natetheorder witheachedition. Astheresultofa
atrueassociationisdetected. fateful coin flip, Tom was first author on the first
Chapters19–21covermethodologicalaspectsof edition, andNoelisnowfirstauthoronthesecond
severalkeytopicsinepidemiology:screeningfordis- edition.
ease, short-term disease outbreaks, and evaluating Wegratefullyacknowledgehelpfulcommentson
the effects of societal and institutional policies on draftchaptersfromseveralcolleaguesandstudents.
health. AliRowhani-Rahbar,PeterCummings,andAmanda
As the book’s title indicates, the discussion Phipps kindly reviewed some of the chapters and
throughoutfocusesonthemeansbywhichepidemi- made many useful suggestions. Several cohorts of
ologicresearchisconductedandinterpreted,noton studentsinourtwo-quartercoursesequenceonepi-
thesubstantiveknowledgeaboutspecificdiseasesor demiologic methods have used the first edition as
exposuresthathasaccumulatedfromspecificstudies. their main textbook and provided feedback about
Twothingsthatwilldistinguishthisbookfrom errorsandpointsofconfusion. Thesecondedition
otherswithsimilargoalsareitsliberaluseofexam- hasbenefitedfromtheirsharpeyes.
plesfrom thepublishedmedical literature, andthe
sets of questions that appear at the end of most NoelS.Weiss
chapters. Most ofthesequestionspertain toactual ThomasD.Koepsell
publishedstudies, ourpurposebeing toemphasize
1
Introduction: An Epidemic of Blindness in
Young Children
DISCOVERY
OnFebruary14,1941,aBostonpediatriciannamed
Dr.StewartCliffordwasmakingaroutinehousecall
ononeofhispatients, ababygirlthenaboutthree
monthsold.Shehadbeenbornprematurely,weigh-
ingaboutfourpoundsatbirth.Butexceptforsome
brief early episodes ofturningblue(cyanosis), she
haddonewellduringherhospitalstayandhadbeen
discharged.
AsDr.Cliffordexaminedher,henoticedsome-
thingoddaboutthebaby’seyes.Hergazewandered
aimlessly, and her eyes jerked rapidly from side to
side. There were prominent gray opacities in both
eyes.Hewaspuzzledandconcerned:byallappear-
ances,thebabygirlwasblind.
Dr.CliffordcalledinDr.PaulChandler,aleading
Bostonophthalmologist.Dr.Chandlerhadnotseen
thisbaby’sconditionbefore.Topermitafullerevalu- FIGURE 1.1 Cross-sectionofaneyeshowingretro-
ation,thebabywashospitalizedagainandexamined lentalfibroplasia.
underanesthesia.Themainabnormality(illustrated (ReprintedcourtesyofDr.ArnallPatz)
inFigure1.1)wasagraymassofscartissueattached
tothebackofthelensandcoveredwithbloodves-
fibroplasia(RLF),referringtoproliferationoffibrous
sels.Itlaterbecameclearthatthistissuewasallthat
scartissuebehindthelens.
remainedofaretinathathadbeensobadlydamaged
byhemorrhageandinflammationthatithaddelam-
inatedfromthebackoftheeye,becomescarredand EPIDEMIC
fibrous,andfloatedforwardtoaffixitselftothelens. Once Dr. Terry’s description of RLF appeared in
Thebabygirlwascompletelyandirreversiblyblind. the medical literature, other physicians began to
Thisfirstcaseprovednottobeabizarre,isolated look for it and to find it. By1945, Dr. Terry pub-
occurrence.Withinaweek,Dr.Cliffordencountered lishedadescriptionof117cases,allbutfiveofthem
anotherblindinfantwiththesamecondition.Soon in babies who had been born prematurely (Terry,
another consultantophthalmologist, Dr. Theodore 1945). Across the country, the California School
Terry, hadgatheredinformation onfivesuchcases fortheBlindreportedasharpriseinthenumberof
in the Boston area, whom he described in an arti- RLF cases over time among babies born in South-
cleintheAmericanJournalofOphthalmology(Terry, ern California, as shown in Figure 1.2 (Silverman,
1942). Shared pathological features among these 1980).Withinjustafewyearsafteritsdiscovery,RLF
early cases led to calling the condition retrolental wentfrombeingliterallyunknowntobeingthemost