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crowded, under-resourced urbanized areas spawn massive shantytowns and high rates of unemployment, desperation and crime. Unbreathable air and depletion of water supplies are major issues. For a vivid and disquieting portrait of some of these situations, see Robert D. Kaplan, The coming anarchy (Atlantic monthly, February 1994; 273:44-76; available at http://www.theatlantic.com/politics/foreign/anarchy.htm). Global epidemiology? Accurate knowledge is an essential for effective action. As illustrated by Ernst Wynder's examples, even partial knowledge can lead to successful prevention. However, partial knowledge can also lead to exchanging one set of problems for another, perhaps worse than those that motivated the original actions. Sir Austin Bradford Hill (1968: 300) wrote that the incomplete and tentative nature of scientific knowledge "… does not confer upon us a freedom to ignore the knowledge we already have, or to postpone the action that it appears to demand at a given time." But the judgment of what action is demanded by existing knowledge is often complex and controversial. The debate between contrasting views of epidemiology outlined earlier reflects to some extent the conflict between the desire to be confident in one's methods and data on the one hand and the need to tackle the major problems that confront public health. But that conflict is one for individuals to resolve in choosing where to work and what to work on, rather than a decision for the field. If epidemiology confines itself to studying biomedical questions that it has the tools for studying, to whom does it leave the other problems that confront public health? If the study of health in human populations is epidemiology, then whether the people who tackle these problems call themselves medical geographers, biological anthropologists, or epidemiologists, they will be practicing epidemiology. Challenges to human health are not constrained by the availability of methodologies to study them. In principle, and increasingly in practice, the purview of epidemiology extends to the fauna and flora of the planet and their global environment. The importance of developing a global perspective becomes clearer every decade, as advances in science, production, transportation, and communication, with the accompanying changes in human activity, have created the conditions for global epidemics, global contamination, conflict between peoples separated by great distances, and even modification of the planet (McMichael 1993). In his book Planetary Overload, Anthony McMichael (1993) identifes international inequality as the key issue that must be addressed in order to protect the global environment on which human health depends: 1. The “one underlying problem is the entrenched inequality between rich and poor countries, which predominantly reflects recent imperial history, power relationships and the global dominance of Western industrial technology and economic values.” (p. 7) 2. The “two central manifestations of this inequality are: 1. rapid, poverty-related, population growth and land degradation in poor countries, and 2. excessive consumption of energy and materials, with high production of wastes, in rich countries.” (p. 7) 3. The “three possible (perhaps coexistent) adverse outcomes of those manifestations are: _____________________________________________________________________________________________ www.sph.unc.edu/courses/EPID168, © Victor J. Schoenbach 2000 17. Epidemiology and public health - 560 rev. 11/8/1998, 8/15/1999, 10/23/1999, 1/17/2000
1. exhausting various non-renewable materials, 2. toxic contamination of localised environments, and 3. impairment of the stability and productivity of the biosphere’s natural systems.” (p. 7) Although the study of the world's people and our environment, living and nonliving, can neither be claimed by nor contained within any discipline or field, epidemiology's multidisciplinary perspective draws, as a matter of course, from all fields of knowledge. In that respect, epidemiology is as logical a field as any to include the study of global health, in its broadest interpretation, within its scope. John Last made this very point in accepting the Abraham Lilienfeld Award from the American College of Epidemiology: "There is a need for innovative, transdisciplinary approaches. Epidemiology is already transdisciplinary. Epidemiology is well placed to take leadership." (American College of Epidemiology Annual Meeting, Boston, September 22, 1997). _____________________________________________________________________________________________ www.sph.unc.edu/courses/EPID168, © Victor J. Schoenbach 2000 17. Epidemiology and public health - 561 rev. 11/8/1998, 8/15/1999, 10/23/1999, 1/17/2000
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Understanding the Fundamentals of E
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Preface Introductory epidemiology c
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Table of Contents Chapter (in Acrob
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1. Introduction Definition, charact
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problems (Schwartz and Carpenter, 1
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HIV - a new or newly-recognized vir
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d = principal investigator's degree
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Analytic studies typically involve
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Observational sciences especially a
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McGavran EG. What is public health?
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2. An evolving historical perspecti
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Time line for the history of public
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as a one-room bacteriology laborato
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− Health surveys − Research fun
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his scientific peers of the correct
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Kuhn, Thomas S. The structure of sc
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3. Studying populations - basic dem
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The demographic balancing equation
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ates. Similarly, bulges in the repr
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When the baby boom cohort retires 1
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The pervasiveness, strength, viciou
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Total fertility rate (TFR) Standard
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Life expectancy The technique, of u
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Excerpt from the U.S. 1993 abridged
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At the other end of the life table,
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to change, hopefully to decline. If
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Thought question: Professors typica
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Descriptive studies and surveillanc
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4. The Phenomenon of Disease Concep
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Classification is the foundation As
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As we gain more sophisticated under
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To recapitulate the above discussio
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Classifying cause of death Since mo
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Laboratory and other objectively me
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distribution but are not diabetic (
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program in the general population,
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Infectious disease Incubation "time
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the direct effects of carcinogenic
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patient outcomes. The design and ev
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detected by screening will appear b
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Morrison, Alan S. Screening in chro
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e relevant. Compromises might be fo
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educational attainment by the numbe
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Distributions - the fuller picture
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Per capita income: Should health ca
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Deaths of children < 1 year of age
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No. of persons with senile dementia
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Incidence Immigration Relationship
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Examples: arthritis, cholelithiasis
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Cohort - entrance into the populati
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Sample calculation: 200 people free
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• The units of time must be state
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Calculation of person-time in a coh
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Original Calculation of person-time
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average risk for a member of the co
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However: Nurses: 601 cases/89,538 w
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treated. If the rate at which patie
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Incidence and prevalence in a popul
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small prevalence. So if the seropre
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Appendix on weighted averages Becau
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Appendix on exponents and logarithm
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and epidemiology. The notation ln(x
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3. For the following hypothetical d
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c. ________________ 6 fatalities /
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Measuring disease and exposure - As
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5. a. Flow Diagram Population of si
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New cases Q ID = ------------------
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Overview 6. Standardization of rate
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differences between the groups in f
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∑ (stratum-specific rates �× s
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especially important when comparing
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copy this cell to the other columns
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where the RR k are the stratum-spec
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and the observed number of deaths i
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Directly standardized rate for A =
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5,022 Indirectly standardized = —
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the situation among older age group
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Appendix on Standardized Mortality
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across age strata, then the damage
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d. How would you feel about the con
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Cases per 100,000 Mean annual incid
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d. dt Indirectly standardized rates
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The second ingredient for an standa
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Group US rate /100,000 County pop.
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Crude rates are comparable because
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The "Big Picture" 7. Relating risk
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Consider first the table on the lef
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The epidemiologist first arranges t
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(I1 - I0)/I0 = (0.01200-0.00800 / 0
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Descriptive adjectives for magnitud
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Odds ratio The odds ratio (OR) is a
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Duncan C. Thomas, "On the need for
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6. Odds of exposure in controls Pro
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CID = CI1 - CI0 = .20 - .10 = .10 (
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When both disease and exposure have
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variables is linear. An r of zero m
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2. In HIV-discordant couples in whi
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Incidence Diagrammatic representati
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PAR = AR × P1 = (I1 - I0)P1 = I -
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expresses the prevented cases as a
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Incidence Diagrammatic representati
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The result, (NHIH)/(NLIL+NHIH), is
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Proportion with = 0.5 ( 22 --- ) +
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CI may be preferred: � if the hea
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Appendix — Relating risk factors
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By definition, oddsr = risk / (1 -
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Bibliography Measures of effect: Te
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Relating risk factors to health - A
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4. In a study of adverse effects of
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number of "permanent" quits (define
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= I1n1- I0n1 + I0n0 - I0n0 ——
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2. Imprecision in determining the t
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Sometimes the appearance of a new s
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Case-control (case-referent, etc.)
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ealistic setting and results may th
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"ecologic fallacy", the erroneous i
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can vary substantially among indivi
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e estimated from that study since t
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Risk ratio Consider the example of
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Dietary Salt Intake and hypertensio
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Intervention trials can include tes
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Treatment allocation can be 1) fixe
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Example Cases Case-control studies
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Cases Controls ____________________
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population and that the controls we
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Estrogen users (N1) Nonusers (N0) N
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In the 3 × 10 6 unexposed women-ye
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similar to that in the case group t
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A modern perspective In general, de
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of exposed to unexposed persons sam
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Case-control studies: Armenian, Har
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Wingo, Phyllis A.; Howard W. Ory, P
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Part I Analytic study designs - Ass
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1. Doll and Hill state (page 1451,
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Part I Analytic study designs - Ass
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� Possible motivation to change b
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9. Causal inference * The desire to
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1955:35). Quarantine of sick person
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The mother who replaced the burned-
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As presented in Kleinbaum, Kupper,
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Popper maintains that it is fundame
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1. Is the association real or artef
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Temporality First exposure, then di
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confer upon us a freedom to ignore
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Lave, Lester B.; E.P. Seskin. Epide
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Precision The presence of random va
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the point estimate is based and thu
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methodological literature. Validity
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disease detection may be mistakenly
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In cohort studies, the primary sour
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present, then the D&C would detect
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Controls in an experiment In a true
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Southern endometrial cancer and est
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Cases ` The ` "detection bias" hypo
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from ETS, then a cohort study of ha
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employing lead exposure measures fr
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which the both measures increase in
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coefficient (slope) is to 1.0 and t
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_ _ Se = Pr(D'|D) Sp = PR(D'|D) _ _
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Differential misclassification, how
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subject plus or minus a random nois
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Appendix 2 More on the concern to a
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Bibliography Henneckens and Buring.
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Sackett, D.L.: Bias in analytic res
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e. OPTIONAL: If the reported cumula
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Results from the Evans County Cardi
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2. I1 = incidence in the exposed P1
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makes most sense to view detection
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Sensitivity × cases + (1 - Specifi
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In the factual world, however, we c
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Hypertensive SI participants were t
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3,154 male managers and white colla
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Table 2 Relationship of CHD to Beha
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a group did indeed have higher CHD
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Confounding - comparison of weighte
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Type A smokers) are not very meanin
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Different control groups for hypoth
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Confounding, then, is a function of
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Since the OR is the crossproduct ra
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Case-control study In a case-contro
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First and foremost, a potential con
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is defined in relation to the count
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poor. A scientific basis linking ra
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One way to obtain a better balance
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Stratified analysis is intuitively
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attributed to the exposure of inter
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Bibliography Rothman and Greenland
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Senior P, Bhopal RS. Ethnicity as a
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Some of the relationships just pres
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n1i _______________________________
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2. A 20-year retrospective cohort s
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No. of urinary tract infections Tab
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2. completely attributable to obesi
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5. a. C -- the adjusted relative ri
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of dietary antioxidants. However, c
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epidemiologic research is to identi
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Since the indicator variable (POP)
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Over two decades ago (Causes, Am J
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In this diagram, G and H exhibit ab
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In this situation, the first suffic
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Crude rates as weighted averages Re
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Lung cancer rates by smoking and as
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{B0} Smk Smk Asb. Asb. {B1} {B2} {B
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Notation for joint effects R1 risk
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and R111 = R000 + RD100 + RD010 + R
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RR11 = RR10 × RR01 [End of aside]
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multiplicative model supports the u
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Effect modification as a reflection
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4. Defining subgroups for preventiv
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Bibliography Rothman and Greenland,
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Multicausality: Effect modification
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4. Several studies have shown a syn
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1. Multicausality: Effect modificat
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In these data, or, Expected ROC,SMK
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to drinking in the absence of smoki
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we determine that confounding is pr
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Association between reserpine and b
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R11 R10 × R01 R10 —— = ——
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Hypothetical data on incidence of m
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1. Data conform to an additive mode
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Difference measure - the CID The va
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Distribution of CIR, IDR, OR 0 +1 M
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1 wi = ---------------------------
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5 Y n B 3 n Y C 8 n Y C 4 Y Y D 7 Y
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R11 - R00 = (R10 - R00) + (R01 - R0
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You may well wonder what is the val
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Moreover, the logistic model, we wi
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Key epidemiologic assumptions in th
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a + b1X1 + b2X2 + b3X3 + …) on th
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Wilcosky, Timothy C. and Lloyd E. C
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Data analysis and interpretation Ep
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Range checks Range checks compare e
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� Decisions deferred have to be m
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� Simpler is better � Avoid ext
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educe bias and tend to introduce ad
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data. Perhaps too often generalitie
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When this "analogous experiment" is
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tests are based (e.g., see Sander G
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The probability associated with bei
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conclude that the association is su
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Exposed to diethylstilbesterol? Yes
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For example, suppose that we are co
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The idea behind small studies bias
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Confidence intervals address the qu
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Computing a confidence interval for
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Bibliography General Ahlbom, Anders
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Thompson, W. Douglas. Statistical c
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Appendix Estimating sample size to
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p1 (1 - p1) p2 (1 - p2) σ 2 1 σ 2
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Margin of error (rounded) Point Sam
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Meditations on hypothesis testing a
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Independent replication is the corn
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More meditations on interpreting st
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Part I Data analysis and interpreta
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Part I 1. (a) Restriction Data anal
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9. ORCIG,HYP,OC [multiplicative mod
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15. Practical aspects of epidemiolo
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(CDC, which includes the National I
Page 517 and 518: cardiovascular area -- notably the
Page 519 and 520: Disease Control (CDC) decided again
Page 521 and 522: After submission but before the awa
Page 523 and 524: Journal of Medicine, Jan 14, 1999,
Page 525 and 526: Explore the data � Look at data (
Page 527 and 528: Recently, standardization has come
Page 529 and 530: Riesenberg, Don; Goerge D. Lundberg
Page 531 and 532: 16. Data management and data analys
Page 533 and 534: implications, or suspicions or char
Page 535 and 536: 1.4.1.2 Consistency Consistency is
Page 537 and 538: 1.4.5.1.2 Series Runs in series are
Page 539 and 540: Obviously it will be easier to asse
Page 541 and 542: 2.1.2.1 Statistical There are forma
Page 543 and 544: 2.3.5 Bivariate displays If the sam
Page 545 and 546: errors. Related to this concern is
Page 547 and 548: 3.3 Expected values Perhaps, the si
Page 549 and 550: Despite the best efforts, however,
Page 551 and 552: Complete data cases % distribution
Page 553 and 554: 3.5 Outliers Outliers are now exami
Page 555 and 556: Bibliography Davidson, Fred. Princi
Page 557 and 558: attrib ckd length=$1 label='Check d
Page 559 and 560: 17. Epidemiology and public health
Page 561 and 562: � Geneva - " . . . IFV and allied
Page 563 and 564: public health, since the best oppor
Page 565 and 566: Individual-level versus societal le
Page 567: 14%, so that the burden of the envi
Page 571 and 572: O'Hare WP, Pollard KM, Mann TL, Ken
Page 573 and 574: � Health for all What contributes
Page 575 and 576: Challenges in the environment for e
Page 577 and 578: � What kind of population is requ
Page 579: Bibliography American College of Ep
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