Basic - WHO

1 Basicepidemiology2nd edition R BonitaR BeagleholeT Kjellstr mWHO Library Cataloguing-in-Publication DataBonita, epidemiology / R. Bonita, R. Beaglehole, T. Kjellstr m. 2nd , Robert. m, Tord. Health 92 4 154707 3 (NLM classification: WA 105)ISBN 978 92 4 154707 9 World Health Organization 2006 All rights reserved. Publications of the World Health Organization can be obtained from WHO Press,World Health Organization, 20 Avenue Appia, 1211 Geneva 27, Switzerland (tel.: +41 22 791 2476;fax: +41 22 791 4857; e-mail: Requests for permission to reproduce or translateWHO publications whether for sale or for noncommercial distribution should be addressed to WHOP ress at the above address (fax: +41 22 791 4806; e-mail: designations employed and the presentation of the material in this publication do not imply theexpression of any opinion whatsoever on the part of the World Health Organization concerning the legalstatus of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiersor boundaries.))

2 Dotted lines on maps represent approximate border lines for which there may not yet befull mention of specific companies or of certain manufacturers products does not imply that they areendorsed or recommended by the World Health Organization in preference to others of a similar naturethat are not mentioned. Errors and omissions excepted, the names of proprietary products are distinguishedby initial capital reasonable precautions have been taken by the World Health Organization to verify the informationcontained in this publication. However, the published material is being distributed without warranty ofany kind, either expressed or implied. The responsibility for the interpretation and use of the material lieswith the reader. In no event shall the World Health Organization be liable for damages arising from named authors alone are responsible for the views expressed in this in 1 What is epidemiology?Key messagesThe historical contextOriginsRecent developments in epidemiologyDefinition, scope, and uses of epidemiologyDefinitionScopeEpidemiology and public healthCausation of diseaseNatural history of diseaseHealth status of populationsEvaluating interventionsAchievements in epidemiologySmallpoxMethyl mercury poisoningRheumatic fever and rheumatic heart diseaseIodine deficiency diseasesTobacco use.

3 Asbestos and lung cancerHip fracturesHIV/AIDSSARSS tudy questionsReferencesChapter 2 Measuring health and diseaseKey messagesDefining health and diseaseDefinitionsDiagnostic criteriaMeasuring disease frequencyPopulation at riskIncidence and prevalenceCase fatalityInterrelationships of the different measuresUsing available information to measure health and diseaseMortalityLimitations of death certificatesLimitations of vital registration systemsTowards comparable estimatesDeath ratesInfant mortalityChild mortality rateixxi11111223444556677899101011121515 15151617171822222323232424252626 ContentsiiiMaternal mortality rateAdult mortality rateLife expectancyAge-standardized ratesMorbidityDisabilityHealth determinants, indicators, and risk factorsOther summary measures of population healthComparing disease occurrenceAbsolute comparisonsRelative comparisonsStudy questionsReferencesChapter 3 Types of studiesKey messagesObservations and experimentsObservational studiesExperimental studiesObservational epidemiologyDescriptive studiesEcological studiesEcological fallacyCross-sectional studiesCase-control studiesCohort studiesSummary of epidemiological studiesExperimental epidemiologyRandomized controlled trialsField trialsCommunity trialsPotential errors in epidemiological studiesRandom errorSample sizeSystematic errorSelection biasMeasurement biasConfoundingThe control of confoundingValidityEthical issuesStudy questionsReferencesChapter 4 Basic biostatistics.

4 Concepts and toolsKey messagesSummarizing dataTables and graphsPie charts and component band chartsSpot maps and rate mapsBar charts2728282930313232343435363639393939 3940404143444446494950505151525253535455 565758606063636364646565ivContentsLine graphsFrequency distributions and histogramsNormal distributionsSummary numbersMeans, medians and modeVariances, standard deviations and standard errorsBasic concepts of statistical inferenceUsing samples to understand populationsConfidence intervalsHypothesis tests, p-values, statistical powerThe p-valueStatistical powerBasic methodst-testsChi-squared tests for cross tabulationsCorrelationRegressionLinear regressionLogistic regressionSurvival analyses and Cox proportional hazards modelsKaplan-Meier survival curvesSample size issuesMeta-analysisStudy questionsReferencesChapter 5 Causation in epidemiologyKey messagesThe concept of causeSufficient or necessarySufficient and necessaryA causal pathwaySingle and multiple causesFactors in causationInteractionA hierarchy of causesEstablishing the cause of a diseaseConsidering causationTemporal relationshipPlausibilityConsistencyStren gthDose response relationshipReversibilityStudy designJudging the evidenceStudy questionsReferences 6666676767686969707171717373747575767879 7980818282838383838485868788888989899191 93939595969697 ContentsvChapter 6 Epidemiology and prevention.

5 Chronic noncommunicablediseasesKey messagesThe scope of preventionRecent trends in death ratesPreventive potentialCausation frameworkLevels of preventionPrimordial preventionPrimary preventionPopulation strategyHigh-risk individual strategySecondary preventionTertiary preventionScreeningDefinitionTypes of screeningCriteria for screeningStudy questionsReferencesChapter 7 Communicable diseases: epidemiology surveillance andresponseKey messagesIntroductionDefinitionsRole of epidemiologyThe burden of communicable diseaseThreats to human security and health systemsEpidemic and endemic diseaseEpidemicsEndemic diseasesEmerging and re-emerging infectionsChain of infectionThe infectious agentTransmissionHostEnvironmentInvestig ation and control of epidemicsInvestigationIdentifying casesManagement and controlSurveillance and responseStudy questionsReferencesChapter 8 Clinical epidemiologyKey messagesIntroductionDefinitions of normality and abnormality 9999999910110210310310510510710810911011 0110110114114117117117117118118118119119 1211221231231241251251261261261261271301 31133133133133 viContentsNormal as commonAbnormality associated with diseaseAbnormal as treatableDiagnostic testsValue of a testNatural history and prognosisPrognosisQuality of lifeQuantity of lifeEffectiveness of treatmentUse of evidence-based guidelinesPrevention in clinical practiceReducing risksReducing

6 Risks in patients with established diseaseStudy questionsReferencesChapter 9 Environmental and occupational epidemiologyKey messagesEnvironment and healthImpact of exposure to environmental factorsEvaluation of preventive measuresExposure and doseGeneral conceptsBiological monitoringInterpreting biological dataIndividual versus group measurementsPopulation doseDose effect relationshipsDose response relationshipsAssessing riskRisk assessmentHealth impact assessmentRisk managementEnvironmental health impact assessmentInjury epidemiologyTraffic crash injuriesWorkplace injuryViolenceSuicidesSpecial features of environmental and occupational epidemiologySetting safety standardsMeasuring past exposureHealthy worker effect in occupational studiesContinuing challenges for epidemiologistsStudy questionsReferencesChapter 10 Epidemiology, health policy and planningKey messagesIntroduction13413513513613613713 7138138139140140141141142143145145145146 1471491491501511511521531541551551551551 5515715715715815815915916016016016116116 5165165 ContentsviiHealth policyHealth planningEvaluationHealth policyThe influence of epidemiologyFraming health policyHealth policy in practiceHealth planningThe planning cycleAssessing burdenUnderstanding causesMeasuring effectiveness of interventionsAssessing efficiencyImplementing interventionsMonitoring activities and measuring progressStudy questionsReferencesChapter 11 First steps in practical epidemiologyKey messagesIntroductionSpecific diseasesCritical readingPlanning a research projectChoosing a projectWriting the protocolDoing the researchAnalysing the dataGetting publishedFurther readingFurther trainingStudy questionsAbstractMethodsAnnexAnswers to Study

7 QuestionsIndex16516516516616616716816917 0171172172173174175175176177177177177178 18118118218318318318418518618718718920vi iiContents5 PrefaceBasic epidemiology was originally written with a view to strengthening education,training and research in the field of public health. Since the book was published in1993, more than 50 000 copies have been printed, and it has been translated intomore than 25 languages. A list of these languages and contact addresses of localpublishers is available on request from WHO Press, World Health Organization, 1211 Geneva 27, epidemiology starts with a definition of epidemiology, introduces the his-tory of modern epidemiology, and provides examples of the uses and applications ofepidemiology. Measurement of exposure and disease are covered in Chapter 2 and asummary of the different types of study designs and their strengths and limitationsis provided in Chapter 3. An introduction to statistical methods in Chapter 4 sets thescene for understanding Basic concepts and available tools for analysing data andAs with the first edition of Basic epidemiology, examples are drawn from differentcountries to illustrate various epidemiological concepts.

8 These are by no means ex-haustive or comprehensive and we encourage students and teachers to seek locallyrelevant examples. Each chapter starts with a few key messages and ends with a seriesof short questions (answers are provided) to stimulate discussion and review authors gratefully acknowledge contributions to the first edition fromJohn Last and Anthony McMichael. Martha Anker wrote Chapter 4 for the firstedition. In the second edition, Chapter 4 was written by Professor O. Dale version of the course material upon which this chapter is based is available A number of corrections to the equations inChapter 4 have been included in the second printing of this International Programme on Chemical Safety (a joint programme of theUnited Nations Environment Programme, the International Labour Organization, andthe World Health Organization), the Swedish International Development Authority(SIDA) and the Swedish Agency for Research Cooperation with Developing Countries(SAREC) all supported the original development of this the impact of interventions.

9 A fundamental task of epidemiologists isto understand the process of making causal judgements, and this is covered inChapter 5. The applications of epidemiology to broad areas of public health are cov-ered in the following chapters: chronic noncommunicable disease (Chapter 6),communicable disease (Chapter 7), clinical epidemiology (Chapter 8) and environ-mental, occupational and injury epidemiology (Chapter 9); the process of healthplanning is outlined in Chapter 10. The final chapter, Chapter 11, introduces the stepsthat new epidemiologists can take to further their education and provides links to anumber of current courses in epidemiology and public addition, the authors would like to thank the following people for theircontributions to the second edition: Michael Baker, Diarmid Campbell-Lendrum,Carlos Corvalen, Bob Cummings, Tevfik Dorak, Olivier Dupperex, Fiona Gore, AlecIrwin, Rodney Jackson, Mary Kay Kindhauser, Doris Ma Fat, Colin Mathers, HoomenMomen, Neal Pearce, Rudolpho Saracci, Abha Saxena, Kate Strong, Kwok-Cho Tang,Jos Tapia and Hanna Tolonen.

10 Laragh Gollogly was managing editor, and graphicdesign was done by Sophie Guetanah-Aguettants and Christophe essential role of epidemiology is to improve the health of populations. This text-book provides an introduction to the Basic principles and methods of is intended for a wide audience, and to be used as training material for professionalsin the health and environment fields. The purpose of this book is to:xexplain the principles of disease causation with particular emphasis on modifiableenvironmental factors, including environmentally-determined behaviours,xencourage the application of epidemiology to the prevention of disease and thepromotion of health,xprepare members of the health-related professions for the need for health servicesto address all aspects of the health of populations, and to ensure that health re-sources are used to the best possible effect, andxencourage good clinical practice by introducing the concepts of the end of the course the student should be able to demonstrate knowledge of.