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Epidemiology for Public Health Practice Robert H. Friis, PhD Professor, Emeritus, and Chair Emeritus Health Science Department California State University Long Beach, California
Thomas A. Sellers, PhD, MPH Director Moffitt Cancer Center & Research Institute Tampa, Florida
FIFTH EDITION
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Library of Congress Cataloging-in-Publication Data Friis, Robert H. Epidemiology for public health practice / Robert H. Friis and Thomas Sellers.—5th ed. p. ; cm. Includes bibliographical references and index. ISBN 978-1-4496-5158-9 (pbk.) I. Sellers, Thomas A. II. Title. [DNLM: 1. Epidemiology. 2. Epidemiologic Methods. 3. Public Health. WA 105] 614.4—dc23
2012039130
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New to This Edition …………………………………………… ix
Introduction ……………………………………………………… xiii
Preface ……………………………………………………………… xvii
Acknowledgments ……………………………………………… xix
About the Authors …………………………………………………… xxiii
Chapter 1 History and Scope of Epidemiology ……………………… 1 Introduction …………………………………………………………. 2 Epidemiology Defined ……………………………………………. 8 Foundations of Epidemiology ………………………………….. 15 Historical Antecedents of Epidemiology ……………………. 23 Recent Applications of Epidemiology ……………………….. 41 Conclusion …………………………………………………………… 48 Study Questions and Exercises …………………………………. 49 References …………………………………………………………….. 51
Chapter 2 Practical Applications of Epidemiology ………………… 55 Introduction …………………………………………………………. 56 Applications for the Assessment of the Health Status of Populations and Delivery of Health Services ………….. 59 Applications Relevant to Disease Etiology ………………….. 83 Conclusion …………………………………………………………… 101 Study Questions and Exercises …………………………………. 101 References …………………………………………………………….. 104
Contents
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Chapter 3 Measures of Morbidity and Mortality Used in Epidemiology ………………………………………………… 107
Introduction …………………………………………………………. 108 Definitions of Count, Ratio, Proportion, and Rate ……… 108 Risk Versus Rate; Cumulative Incidence ……………………. 121 Interrelationship Between Prevalence and Incidence ……. 124 Applications of Incidence Data ………………………………… 126 Crude Rates ………………………………………………………….. 126 Specific Rates and Proportional Mortality Ratio …………. 138 Adjusted Rates ………………………………………………………. 144 Conclusion …………………………………………………………… 151 Study Questions and Exercises …………………………………. 152 References …………………………………………………………….. 155
Chapter 4 Descriptive Epidemiology: Person, Place, Time ……… 157 Introduction …………………………………………………………. 158 Characteristics of Persons ………………………………………… 163 Characteristics of Place …………………………………………… 203 Characteristics of Time …………………………………………… 217 Conclusion …………………………………………………………… 223 Study Questions and Exercises …………………………………. 223 References …………………………………………………………….. 225 Appendix 4—Project: Descriptive Epidemiology of a Selected Health Problem ………………………………….. 233
Chapter 5 Sources of Data for Use in Epidemiology ………………. 235 Introduction …………………………………………………………. 236 Criteria for the Quality and Utility of Epidemiologic Data …………………………………………… 239 Online Sources of Epidemiologic Data ……………………… 241 Confidentiality, Sharing of Data, and Record Linkage …. 244 Statistics Derived from the Vital Registration System ….. 247 Reportable Disease Statistics ……………………………………. 254 Screening Surveys ………………………………………………….. 259 Disease Registries …………………………………………………… 260 Morbidity Surveys of the General Population …………….. 262 Insurance Data………………………………………………………. 267 Clinical Data Sources ……………………………………………… 267 Absenteeism Data ………………………………………………….. 271 School Health Programs …………………………………………. 272
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Morbidity in the Armed Forces: Data on Active Personnel and Veterans ………………………………………. 272 Other Sources: Census Data ……………………………………. 273 Conclusion …………………………………………………………… 274 Study Questions and Exercises …………………………………. 274 References …………………………………………………………….. 276
Chapter 6 Study Designs: Ecologic, Cross-Sectional, Case-Control …………………………………………………. 279
Introduction …………………………………………………………. 280 Observational Versus Experimental Approaches in Epidemiology ……………………………………………………. 281 Overview of Study Designs Used in Epidemiology ……… 282 Ecologic Studies …………………………………………………….. 287 Cross-Sectional Studies …………………………………………… 294 Case-Control Studies ……………………………………………… 303 Conclusion …………………………………………………………… 317 Study Questions and Exercises …………………………………. 317 References …………………………………………………………….. 319
Chapter 7 Study Designs: Cohort Studies …………………………….. 323 Introduction …………………………………………………………. 324 Cohort Studies Defined ………………………………………….. 325 Sampling and Cohort Formation Options …………………. 335 Temporal Differences in Cohort Designs …………………… 341 Practical Considerations ………………………………………….. 344 Measures of Effect: Their Interpretation and Examples … 347 Summary of Cohort Studies …………………………………….. 358 Conclusion …………………………………………………………… 359 Study Questions and Exercises …………………………………. 362 References …………………………………………………………….. 363
Chapter 8 Experimental Study Designs ……………………………….. 367 Introduction …………………………………………………………. 368 Hierarchy of Study Designs …………………………………….. 371 Intervention Studies ……………………………………………….. 373 Clinical Trials ……………………………………………………….. 374 Community Trials …………………………………………………. 392 Conclusion …………………………………………………………… 404 Study Questions and Exercises …………………………………. 405 References …………………………………………………………….. 406
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Chapter 9 Measures of Effect ……………………………………………… 409 Introduction …………………………………………………………. 410 Absolute Effects …………………………………………………….. 410 Relative Effects ……………………………………………………… 414 Statistical Measures of Effect ……………………………………. 420 Evaluating Epidemiologic Associations ……………………… 423 Models of Causal Relationships ……………………………….. 425 Conclusion …………………………………………………………… 430 Study Questions and Exercises …………………………………. 431 References …………………………………………………………….. 432 Appendix 9—Cohort Study Data for Coffee Use and Anxiety ………………………………………………………. 433
Chapter 10 Data Interpretation Issues …………………………………… 435 Introduction …………………………………………………………. 436 Validity of Study Designs ……………………………………….. 437 Sources of Error in Epidemiologic Research ……………….. 440 Techniques to Reduce Bias ……………………………………… 449 Methods to Control Confounding ……………………………. 450 Bias in Analysis and Publication ……………………………….. 454 Conclusion …………………………………………………………… 456 Study Questions and Exercises …………………………………. 456 References …………………………………………………………….. 458
Chapter 11 Screening for Disease in the Community ………………. 461 Introduction …………………………………………………………. 462 Screening for Disease ……………………………………………… 464 Appropriate Situations for Screening Tests and Programs ………………………………………………………….. 468 Characteristics of a Good Screening Test …………………… 471 Evaluation of Screening Tests ………………………………….. 471 Sources of Unreliability and Invalidity ………………………. 476 Measures of the Validity of Screening Tests ……………….. 476 Effects of Prevalence of Disease on Screening Test Results……………………………………………………………… 479 Relationship Between Sensitivity and Specificity …………. 482 Evaluation of Screening Programs …………………………….. 483 Issues in the Classification of Morbidity and Mortality … 485 Conclusion …………………………………………………………… 486 Study Questions and Exercises …………………………………. 487 References …………………………………………………………….. 488 Appendix 11—Data for Problem 6 …………………………… 490
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Chapter 12 Epidemiology of Infectious Diseases …………………….. 491 Introduction …………………………………………………………. 492 Agents of Infectious Disease …………………………………….. 493 Characteristics of Infectious Disease Agents ……………….. 496 Host ……………………………………………………………………. 497 The Environment ………………………………………………….. 499 Means of Transmission: Directly or Indirectly from Reservoir ………………………………………………………….. 500 Measures of Disease Outbreaks ………………………………… 506 Procedures Used in the Investigation of Infectious Disease Outbreaks ……………………………………………… 511 Epidemiologically Significant Infectious Diseases in the Community ……………………………………………………… 513 Conclusion …………………………………………………………… 539 Study Questions and Exercises …………………………………. 539 References …………………………………………………………….. 542 Appendix 12—Data from a Foodborne Illness Outbreak in a College Cafeteria …………………………… 545
Chapter 13 Epidemiologic Aspects of Work in the Environment …………………………………………………. 547
Introduction …………………………………………………………. 548 Health Effects Associated with Environmental Hazards .. 550 Study Designs Used in Environmental Epidemiology ….. 550 Toxicologic Concepts Related to Environmental Epidemiology ……………………………………………………. 555 Types of Agents …………………………………………………….. 557 Environmental Hazards Found in the Work Setting ……. 571 Noteworthy Community Environmental Health Hazards ……………………………………………………………. 575 Conclusion …………………………………………………………… 588 Study Questions and Exercises …………………………………. 591 References …………………………………………………………….. 592
Chapter 14 Molecular and Genetic Epidemiology …………………… 599 Introduction …………………………………………………………. 600 Definitions and Distinctions: Molecular Versus Genetic Epidemiology ……………………………………………………. 605 Epidemiologic Evidence for Genetic Factors ………………. 609 Causes of Familial Aggregation ………………………………… 610 Shared Family Environment and Familial Aggregation … 612 Gene Mapping: Segregation and Linkage Analysis ………. 616
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Genome-Wide Association Studies (GWAS) ……………… 626 Linkage Disequilibrium Revisited: Haplotypes …………… 628 Application of Genes in Epidemiologic Designs ………….. 631 Genetics and Public Health …………………………………….. 638 Conclusion …………………………………………………………… 642 Study Questions and Exercises …………………………………. 642 References …………………………………………………………….. 643
Chapter 15 Social, Behavioral, and Psychosocial Epidemiology … 649 Introduction …………………………………………………………. 650 Research Designs Used in Psychosocial, Behavioral, and Social Epidemiology …………………………………………… 655 The Social Context of Health ………………………………….. 657 Independent Variables ……………………………………………. 660 Moderating Variables ……………………………………………… 669 Dependent (Outcome) Variables: Physical and Mental Health ……………………………………………………………… 684 Conclusion …………………………………………………………… 691 Study Questions and Exercises …………………………………. 692 References …………………………………………………………….. 694
Chapter 16 Epidemiology as a Profession ………………………………. 701 Introduction …………………………………………………………. 702 Specializations within Epidemiology …………………………. 703 Career Roles for Epidemiologists ……………………………… 705 Epidemiology Associations and Journals ……………………. 708 Competencies Required of Epidemiologists ……………….. 711 Resources for Education and Employment ………………… 712 Professional Ethics in Epidemiology …………………………. 714 Conclusion …………………………………………………………… 719 Study Questions and Exercises …………………………………. 720 References …………………………………………………………….. 721
Appendix A—Guide to the Critical Appraisal of an Epidemiologic/Public Health Research Article …… 723
Appendix B—Answers to Selected Study Questions … 727
Glossary ……………………………………………………………. 737
Index ………………………………………………………………….. 759
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New to This Edition
Chapter 1: History and Scope of Epidemiology
●● New and updated images ●● Updated chart: three presentations of epidemiologic data ●● Updated chart: pneumonia and influenza mortality ●● New chart on the interdisciplinary nature of epidemiology ●● Glossary of terms used in the yearly bill of mortality for 1632 ●● Expanded information on cholera and John Snow
Chapter 2: Pract ical Applicat ions of Epidemiology
●● Updated information on leading causes of death from 1900 to 2009 ●● Expanded discussion of population dynamics and predictions about the future ●● More information provided on the health of the community and health
disparities, including the GINI index
Chapter 3: Measures of Morbidity and Mortal i ty Used in Epidemiology
●● Expanded coverage of epidemiologic measures (e.g., sex ratios) ●● More information on prevalence given with figure to show interrelationships
between prevalence and incidence ●● Further clarification of perinatal mortality provided
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Chapter 4: Descript ive Epidemiology: Person, Place, Time
●● Updated coverage of morbidity and mortality data by descriptive epidemiologic variables provided throughout the chapter
●● New examples of case studies and case series ●● New information on age effects associated with morbidity and mortality ●● Many new charts added to this chapter ●● Updates from the 2010 Census, with current definitions of race/ ethnicity
Chapter 5: Sources of Data for Use in Epidemiology
●● Updated information on data sources including notifiable diseases ●● Further clarification of criteria for the quality of epidemiologic data ●● Rationale strengthened for the need for high-quality epidemiologic data
Chapter 6: Study Designs: Ecologic, Cross- Sectional , Case-Control
●● Clarification regarding design and applications of case-control studies ●● More information on matching in case-control studies ●● Clearer definitions of terms provided ●● Further discussion of comparisons between cross-sectional and case-
control studies
Chapter 7: Study Designs: Cohort Studies
●● Introduction updated ●● Additional clarification of terminology used in cohort studies ●● Exhibit on life table methods updated to the most recent information
Chapter 8: Experimental Study Designs
●● Expanded coverage of intervention studies ●● Several new images, including an image of a scurvy victim ●● Discussion of phase 4 clinical trials ●● New table and a glossary of terms used in clinical trials ●● Applications of epidemiology to vaccines and prevention: HPV vaccine
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Chapter 9: Measures of Effect
●● Introduction revised ●● STROBE guidelines and quality of epidemiologic studies ●● Meta-analysis and systematic reviews
Chapter 10: Data Interpretat ion Issues
●● More information on Simpson’s Paradox, including a new figure ●● Information bias and screening mammography
Chapter 11: Screening for Disease in the Community
●● New figure showing participants in a mammogram and a blood pressure screening test
●● New figure showing participation rates in screening for colorectal cancer, breast cancer, and cervical cancer
●● Updated discussion on controversies in screening ●● Difficulties with false positive screening test results
Chapter 12: Epidemiology of Infect ious Diseases
●● Many updated charts showing data on disease incidence and prevalence (e.g., measles, malaria, hepatitis, valley fever, Lyme disease)
●● Information on the cholera epidemic in Haiti ●● Revised exhibit on viral hepatitis
Chapter 13: Epidemiologic Aspects of Work in the Environment
●● New information on methodologic topics (e.g., exposure assessments, clustering, and confounding)
●● Updated data on blood lead levels and mercury advisories ●● New topics include global warming, the BP oil spill, and the Japanese
tsunami and its effects on the Fukushima nuclear reactor ●● Many new images to capture students’ interest in this topic
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Chapter 14: Molecular and Genetic Epidemiology
●● New diagram of Mendelian inheritance ●● Additional discussion of the population genetics concept of linkage
disequilibrium ●● Expanded discussion of the concept of haplotypes ●● A thorough update of this chapter with the latest developments in the field
Chapter 15: Social , Behavioral , and Psychosocial Epidemiology
●● Many new illustrations added to this chapter ●● The concept of community-based participatory research added ●● New information on the social context of health (e.g., poverty, the Glasgow
effect) ●● Healthy People 2020 overarching goals included ●● Update on depression
Chapter 16: Epidemiology as a Profession
●● Updated to show current professional resources and issues
Other
●● Exciting new figures, tables, and exhibits provided throughout ●● Additional exercises and study questions
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Introduction
Epidemiology is an important, exciting, and rewarding field for the public health practitioner! Almost daily, one hears dramatic media reports about flare-ups of diseases, either previously known or seemingly new conditions. These accounts demonstrate how epidemiologists help to uncover the causes of human illnesses in the population and thereby underscore the importance of epidemiology to society. Deadly outbreaks of communicable diseases, the ongoing threat of resur- gent epidemics, and the possible intentional spread of pathogenic microorgan- isms through acts of bioterrorism present challenges to the field. By assisting the reader in understanding why and how diseases occur and how they may be pre- vented, epidemiology is a valuable pursuit. In this text you will learn that many epidemiologic investigations into the causes of mysterious outbreaks are similar to detective work.
One of the challenges for the authors has been to distill with sufficient breadth and depth all of the fascinating components of this discipline. As the Fifth Edition is being finalized, new and resurgent health conditions challenge public health practitioners; some current examples are resurgent whooping cough, outbreaks of foodborne diseases, hantavirus infections (which normally are infrequent) in a national park, fungal meningitis associated with epidural steroid injections, and a West Nile virus epidemic. Thus, the ongoing flow of accounts of disease outbreaks (noted in the First Edition) has not been staunched and, in fact, is con- tinuing unabated during the second decade of the 21st century.
Since the publication of the earlier editions of this book, the wealth of epidemiologic research findings has continued to proliferate and win the atten- tion of the popular media and professional journals. For example, some of these recent discoveries relate to continuing advances in genetics and molecu- lar biology, recognition of emerging infections, and the growing use of the Internet. As a result, the Second Edition introduced several enhancements: a new chapter on molecular and genetic epidemiology, a new chapter on experimental
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epidemiology, material on epidemiology Internet sites, and updated charts and tables throughout the text.
The Third Edition incorporated a new chapter on cohort designs, a glossary, and an expanded coverage of ecologic and case-control study designs. The Third Edition also included new material on the role of epidemiology in policy making, epidemiology and geographic information systems, and the definition of race used in Census 2000. A new Appendix A provided an extended guide to critiqu- ing published research studies in public health and epidemiology. Several new tables summarized unadjusted measures of morbidity and mortality, contrasted different types of observational study designs, and compared observational versus intervention study designs.
The Fourth Edition presented new information on infectious disease threats associated with E. coli foodborne illness and avian influenza as well as expanded coverage of the historical background of epidemiology. Chapter 3, “Measures of Morbidity and Mortality Used in Epidemiology,” was updated
