Concepts of Epidemiology: An integrated introduction to the ideas, theories, principles and methods of epidemiology

346 Pages·2002·2.26 MB·English

by  Raj Bhopal

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Concepts of Epidemiology
An integrated introduction
to the ideas, theories,
principles and methods of
epidemiology
This page intentionally left blank
Concepts of
Epidemiology
An integrated introduction
to the ideas, theories,
principles and methods of
epidemiology
Raj S. Bhopal
Alexander Bruce and John Usher Professor of Public Health
and
Head, Department of Community Health Sciences
University of Edinburgh, Scotland
formerly
Professor of Epidemiology and Public Health
University of Newcastle Upon Tyne
1
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1
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British Library Cataloguing in Publication Data
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Bhopal,Raj S.
Concepts ofepidemiology :an integrated introduction to the ideas,theories,
principles,and methods ofepidemiology / by Raj S.Bhopal.
Includes bibliographical references.
1.Epidemiology.I.Title.
[DNLM:1.Epidemiology.WA 105 B575c 2002]
RA650 .B48 2002 614.4—dc21 2001052327
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Foreword
When I was learning epidemiology in the late 1950s,I was inspired by the first edition
ofJerry Morris’s now classic little monograph,Uses ofEpidemiology,but there were
hardly any comprehensive current textbooks to guide me.The few available books
were either unreadable,unhelpful,or failed to orient my thoughts along the directions
my ideas were taking.How times have changed! Now there are so many good books
that it is difficult for the uninitiated to select the most suitable one to meet their needs.
In 1997,Raj Bhopal reviewed twenty-five textbooks ofepidemiology,discussing their
approach to the subject,and their strengths and weaknesses,in a critical commentary
that is helpful to teachers and learners alike. Now,from the University ofEdinburgh
(where I spent five happy years in the 1960s),Raj Bhopal,who holds the Usher chair of
public health,has written his own introductory textbook for graduate students who
are embarking upon the detailed study ofepidemiology.
This is an excellent introduction.Raj Bhopal’s approach is conceptual—he describes
and explains the underlying concepts and methods ofepidemiology with clarity and
with apt examples,and simple,elegant illustrations.Frequently throughout the text he
asks penetrating questions that will test the limits ofhis readers’intellectual capacity—
an admirable feature that other authors could copy with benefit to themselves and
their readers.All the essentials are here:the person-population dyad,variation,error,
bias,confounding,causality,the spectrum ofdisease,the ‘iceberg’concept,risk and its
relationship to disease frequency,study design,the ethical framework within which we
practise epidemiology and conduct research,the relationship ofepidemiology to other
scholarly pursuits,and finally, some thoughts about the way the discipline has evolved
and is likely to continue to evolve in the lifetime ofthose now entering upon careers in
this field.
IfI may speak directly to students starting the study ofepidemiology: you can be
grateful that there is a book like this to guide you along the fascinating pathway that
leads to epidemiological enlightenment and understanding.This book will enable you
to comprehend the connections between individual and population health,the natural
history ofdisease,the methods ofepidemiology,the interventions that work and don’t
work,and the role ofepidemiology as the fundamental public health science. This is a
book for you to buy,to read,to study,and to enjoy.
John M.Last
Emeritus Professor ofEpidemiology,
University ofOttawa
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I dedicate this book to my mother Bhagwanti Kaur Bhopal for impressing on me
(and my siblings) the importance ofeducation,and encouraging us to make up for
her own lack ofschooling and formal education;and to my father Jhanda Singh
Bhopal for setting an example ofhow to work hard,shoulder responsibility,and
strive for self-improvement.
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Preface
The purpose ofthis book is to explain and illustrate the key concepts which underpin
the science of epidemiology and its applications to research,policy making,health
service planning and health promotion.The book emphasizes theory,ideas,and
epidemiological axioms.In doing this I hope to counter the mounting criticism that
epidemiology is an atheoretical discipline.
A concept is an idea,but the word is usually reserved for complex,or interrelated,
ideas.A concept is the idea behind the word or phrase we use to describe something.
This book,then,aims to explain the ideas underlying the language,principles,and
basic methods in epidemiology.For example,the attributable risk and odds ratios are
not considered merely as arithmetical equations or tools,but also in terms ofthe ideas
underlying their calculation,applications,strengths,and limitations.
This book is primarily written for postgraduates beginning courses on epidemiology
anywhere in the world,for the concepts are the same everywhere.Only the examples will
differ.The book may be ofinterest to public health and other epidemiological practi-
tioners interested in revisiting the fundamental ideas oftheir discipline.Undergraduates
who are keen on epidemiology may find it helpful in deepening their understanding
generally,or while studying some topics in a little depth.Health professionals (including
busy doctors) may find this material an interesting adjunct to their use ofepidemiologi-
cal techniques or data.Finally,health service managers and policy makers may find this
book a source ofinsights into the world ofepidemiology.
There are 10 chapters.Many introductory courses are designed around 10–15 or so
sessions.I envisage that the core ofthis book could be grasped in 10 days ofcommitted
study,preferably in the context ofa taught course,but also independently.
The book is written in plain language but a basic understanding ofbiology is needed,
as is some familiarity with illness and disease.However,medical terminology is
explained and defined in a glossary.The learning objectives are expressed in terms of
the reader acquiring understanding.I believe that achieving understanding is the high-
est form oflearning;from that may flow a lasting and usable knowledge base,change
ofattitude,and the achievement ofskills.There are exercises to help readers to deepen
their understanding.Each chapter ends in a summary.
The motivation to write this book came from two directions,one in academia,the
other in public health practice.As an examiner ofboth undergraduate and postgradu-
ate students I was surprised,and crestfallen,to see how many students could not
clearly explain basic ideas such as the difference between a case-control and cohort
study,sometimes even after a year ofstudy.In my duties in the health service I partici-
pated in many discussions on why service demands exceeded supply even after new
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viii PREFACE
investments were made.Not once did anyone invoke the crucial concept ofthe iceberg
of disease and symptoms to explain this phenomenon,and clearly even those who
knew ofit did not make the leap from the classroom to the boardroom.This book is
deliberately discursive,not simply descriptive,to help readers to achieve a deeper
understanding and to help bridge the world oftheory to that ofpractice.
Students rapidly grasp the importance and worth ofstudying concepts,and demand
more.The depth ofunderstanding ofconcepts gained from most books and courses is
insufficient to permit students to apply what they have learned to the problems they
are to solve.The acid test ofthis book is whether readers find themselves using epi-
demiological concepts in their everyday work,not seeing them merely as theoretical
constructs for the classroom and examination hall.
The conceptual frameworks within which the practice ofepidemiology operates take
a slightly different perspective from those ofthe science ofepidemiology.The nature of
research questions,the relative value ofthe various methods,and the approach to data
analysis,presentation,and interpretation differ.This book demonstrates these differ-
ences and makes the implications explicit.
The book places heavy emphasis on integrating the ideas ofepidemiology.The inter-
dependence ofepidemiological studies and their essential unity is an important theme
ofthis book.It is,therefore,designed to be read as a whole,either as a foundation text
or as a refresher.Each chapter,however,can be read independently ifnecessary,with
cross-references to other chapters for required definitions.
This book differs in many ways from alternatives,for example:
(cid:2) The concepts ofepidemiology are discussed in detail,and in an integrated way.
(cid:2) The concepts are dominant whereas in other books the methods dominate.
(cid:2) The epidemiological idea of population is explicitly the foundation of the whole
book. In most other books the population idea is implicit and in some it is
neglected.
(cid:2) The practical applications of each concept are considered,and illustrated with
examples drawn from contemporary research and public health practice,including
healthcare policy and planning.The idea is that the reader will acquire the depth of
knowledge to use the concepts and not merely be aware ofthem.
(cid:2) The work is rooted in the basic ideas of the science of epidemiology,which are
wholly applicable worldwide,not just in Europe or North America.
(cid:2) The emphasis is on gaining understanding,and not on calculations,except where
this is essential to understanding.
(cid:2) Most ofthe exercises require reflection not calculation.
In short this textbook focuses on a theme which is the most important in any science,
is too often overlooked,and which students demand more of:concepts.
R.S.B
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Acknowledgements
My foremost debt is to the innumerable people who have taught me,whether in the
classroom,seminar,and conference,or by their writings.One absorbs ideas and facts
from others and over time synthesizes them with one’s own thoughts and experiences.
Eventually,it is impossible to distinguish one’s own ideas from those ofothers.Ifmy
readers recognize their own ideas,and think they are incompletely acknowledged,then
please accept my thanks and let me know.
Needless to say,I am responsible for all remaining errors offact or interpretation—
readers would do me a great favour by alerting me to any they discover (E-mail
[email protected]).
Many people have helped me by giving encouragement,information,constructive
criticism,and by helping to prepare the manuscript.I can list only a few here;the
others are not forgotten.
Marcus Steiner,an MSc (Epidemiology) student and graduate at Edinburgh University,
was my postgraduate reader-critic and helper.His advice and help,particularly with the
technical preparation and development ofthe figures,was immensely useful.His com-
ment after reading an early draft,‘I wish I knew all this before’,was highly motivating to
me at times ofdifficulty.
Dr Sonja Hunt stimulated me to think about figure 10.1.Dr Colin Fischbacher
helped me proof-read the manuscript and made many several thoughtful observations.
Professor John Last enthusiastically agreed to write the foreword.
Others who provided academic advice on one or more specific chapters include:
Professor Carl Shy,Dr David Chappel,Dr Eileen Kaner,and four anonymous referees
who commented on the book proposal and chapter outlines.
I thank Dr Mike Lavender for permission to use extracts from our joint unpublished
paper on the role ofepidemiology in priority setting,and co-authors on various publi-
cations that I have drawn on (these are referenced).I have drawn heavily on my publi-
cations to prepare Chapter 10 and acknowledgements are given below.
Helen Liepman,Commissioning Editor at Oxford University Press,deserves thanks
for her enthusiasm,expert support,and patience.
I conceived this book while in my post as Professor of Epidemiology and Public
Health at the University ofNewcastle upon Tyne,England.The embryonic and fetal
growth stages ofthe idea were nourished during my sabbatical at the Department of
Epidemiology ofthe School ofPublic Health at the University ofNorth Carolina at
Chapel Hill,and on my return to Newcastle.The birthplace ofthe book,however,was
in Edinburgh,during my tenure as Alexander Bruce and John Usher Professor of
Public Health in the Section of Public Health,Department of Community Health