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Therearemanygoodepidemiologytextbooksonthemarket,butmostoftheseare addressedtostudentsofpublichealthorpeoplewhodoclinicalresearchwithe- demiologicmethods. Thereisaneedforashortintroductiononhowepidemiologic methodsareusedinpublichealth,geneticandclinicalepidemiology,becausehealth professionalsneedtoknowbasicepidemiologicmethodscoveringetiologicaswell asprognosticfactorsofdiseases. Theyneedtoknowmoreaboutmethodologythan introductorytextsonpublichealthhavetooffer. Insomehealthfaculties,epidemiologyisnotevenpartoftheteachingcurri- lum. Webelievethistobeaseriousmistake. Medicalstudentsarestudentsofall aspectsofdiseasesandhealth. Withoutknowingsomethingaboutepidemiologythe cliniciansandotherhealthprofessionalscannotreadagrowingpartofthesci- ti cliteratureinanyreasonablycriticalwayandcannotnavigateintheworldof evidence-basedmedicineandevidence-basedprevention. Withoutskillsine- demiologicmethodologytheyareinthehandsofexpertsthatmaynotonlyhavean interestinhealth. Some health professionals may believe that only common sense is needed to conductepidemiologicalstudies,butthescienti cliteratureandthepublicdebate onhealthissuesindicatethatcommonsenseisofteninshortsupplyandmaynot thrivewithoutsomeformaltraining. Epidemiologic methods play a key role in identifying environmental, social, and genetic determinants of diseases. Clinical epidemiology addresses the tr- sitionfromdiseasetohealthortowardmortalityorsocialormedicalhandicaps. Publichealthepidemiologyaddressesthetransitionfrombeinghealthytobeingnot healthy. Descriptiveepidemiologyprovidesthediseasepatternthatisneededtolook athealthinabroadperspectiveandtosettheprioritiesright. Epidemiologyisabasic scienceofmedicinewhichaddresseskeyquestionssuchas Whobecomesill? and Whatareimportantprognosticfactors? Answerstosuchquestionsprovidethe basisforbetterpreventionandtreatmentofdiseases. Many people contributed to the writing of this book: medical students in Denmark,studentsofepidemiologyattheIEAEEPEsummercourseinFlorence, Italy,andstudentsofpublichealthinLosAngeles. Withouttechnicalassistance v vi Preface fromGitteNielsen,JenadeShelley,NinaHoheandPamMasangkaythebookwould neverhavematerialized. LosAngeles,California JornOlsen Odense,Denmark KaareChristensen IowaCity,Iowa JeffMurray Stockholm,Sweden AndersEkbom Contents Part I Descriptive Epidemiology 1 Measures of Disease Occurrence …3 IncidenceandPrevalence …4 Incidence…6 RatesandDynamicPopulations …7 CalculatingObservationTime…9 Prevalence,Incidence,Duration …10 MortalityandLifeExpectancy …11 LifeExpectancy …12 References…13 2 Estimates of Associations …15 3 Age Standardization…19 4 Causes of Diseases …23 References…28 5 Descriptive Epidemiology in Public Health…29 GraphicalModelsofCausalLinks …33 References…35 6 Descriptive Epidemiology in Genetic Epidemiology…37 OccurrenceDatainGeneticEpidemiology …37 ClusteringofTraitsandDiseasesinFamilies …38 TheOccurrenceofGeneticDiseases …40 References…41 7 Descriptive Epidemiology in Clinical Epidemiology…43 SuddenInfantDeathSyndrome(SIDS)…44 CytologicalScreeningforCervixCancer …45 ChangesinTreatmentofJuvenileDiabetes …46 References…47 vii viii Contents Part II Analytical Epidemiology 8 Design Options…51 CommonDesignsUsedtoEstimateAssociations…51 EcologicalStudy …52 Case-ControlStudy…54 CohortStudy …5 5 ExperimentalStudy …56 Reference …57 9 Follow-Up Studies …59 TheNon-experimentalFollow-Up(Cohort)Study …59 StudyingRiskasaFunctionofBMI …60 LongitudinalExposureData…62 DifferentTypesofCohortorFollow-UpStudies…63 10 Case-Control Studies…67 Case-CohortSampling …69 DensitySamplingofControls…69 Case-Non-caseStudy…71 PatientControls …72 SecondaryIdenti cationoftheSourcePopulation …74 Case-ControlStudiesUsingPrevalentCases…74 WhentoDoaCase-ControlStudy? …77 References…78 11 The Cross-Sectional Study…79 12 The Randomized Controlled Trial (RCT) …81 Reference …
