limits of epidemiology - international physicians for the prevention

Epidemiology is the field of study ofhealth and disease in populations. Assuch it is considered to be the basic sci-

ence of public health, the activity of pre-venting disease and promoting health in pop-ulations [1]. This focus on primary preven-tion of disease in large groups has distin-guished public health from medicine, whichfocuses on treatment and prevention of dis-ease in individual patients. To provide thebasic science for public health, as the clinical

disciplines do for medicine, epidemiologymust try to explain, and thereby suggestways to improve, the experience of diseaseand health in populations as distinct fromindividual patients.

Treatment for a patient is affected by theexplanations that the basic medical sciencesprovide for a particular condition. Thus onekind of basic science suggests a pharmaco-logical treatment, while another suggests anutritional intervention. Furthermore, theunderstanding of pathological processeschanges over time with basic scientificknowledge and the experience of clinicalapplication, so that medical approaches fortreating a given condition change.

Similarly, public health policy dependson epidemiological explanations of health

74 Medicine & Global Survival 1994; Vol. 1, No. 2 Limits of Epidemiology

Limits of Epidemiology

Steve Wing

At the time of publication, SW was AssistantProfessor, Department of Epidemiology, Schoolof Public Health, University of North Carolina,Chapel Hill, NC USA.

© Copyright 1994 Medicine and Global Survival

§

Epidemiology is called the "basic science of public health," but its contribution to thisgoal is constrained by a preoccupation with supposedly universal exposure-diseaserelationships that impedes consideration of the contexts in which exposures occur.Epidemiological studies of radiation and health, dominated by interest in radiation-cancer dose response, are a classical example. Radiation epidemiology uses anexperimental model of investigation in which the sources of exposures and the otherchanges that occur because of their production are excluded from scientific interest.In this approach, problems of comparability and measurement are the primary obsta-cles to identifying underlying dose response phenomena. However, because expo-sure-disease relationships are not self-contained, homogeneous or independent phe-nomena, they constitute an inadequate object of epidemiological science. Historicaland contemporary examples show that exposure-disease studies can be integratedinto a broader public health perspective in which specific exposures are consideredas agents acting in a context rather than as autonomous causes of disease. Publichealth interventions narrowly focused on exposure-disease relationships cannotaddress the more important public health effects of the industries and social arrange-ments that produce exposures studied by epidemiologists. Epidemiology can dra-matically improve its contribution to public health and achieve a far greater level ofsocial responsibility by recognizing the historical contexts of public health phenome-na and the sciences that address them. [M&GS 1994; 1:74-86]

and disease in populations. These explana-tions, as in any science, depend on the con-cepts and methods used to understand agiven problem. Epidemiology is a fairlyyoung discipline, yet it has undergone a vari-ety of changes, including those brought on bythe hygiene movement, the bacteriologicalrevolution, the increasing application of sta-tistical survey methods, molecular biology,and the environmental movement.

Despite a history of changing ideasabout the causes and treatments of disease inpopulations, modern quantitative epidemiol-ogy is increasingly presented as the objectivetechnique for uncovering universal lawsabout causes of disease in populations [2]. Itis increasingly applied in clinical medicine,and some claim that it is a generic tool thatcan be used for the investigation of anyhuman condition [3]. All sciences change incharacter over time, however, and the currentdominant epidemiological practice is not, inhistorical terms, the end of the road, butrather a particular form of inquiry and expla-nation that will continue to be transformed inthe context of changes in public health, med-icine, science and society.

This paper first describes the characterof explanation in modern epidemiology, apractice that has coalesced in English-speak-ing countries during the latter half of thetwentieth century [4]. Conceptual problemswith the object of inquiry in modern epi-demiology are raised which suggest the fieldshould adopt a less reductionistic approach.Some examples of alternative epidemiologi-cal perspectives are given in the third section.The limits of modern epidemiology in publichealth practice are considered in the fourthsection, and the final section addresses issuesof scientific objectivity and social responsibil-ity. Epidemiological investigation of healtheffects of ionizing radiation is used as a pri-mary example.

Explanation in ModernEpidemiology

The dominant mode of epidemiologicalexplanation takes place fully within the limitsof a scientific practice that has been termedCartesian reductionism, an analyticalapproach characterized by a focus on factorsconsidered in isolation from their context (Fig1) [5]. Disease in populations, the stated focusof the discipline and the central feature dis-tinguishing epidemiology from the clinicalsciences, is to be explained in terms of a seriesof agents, exposures, or risk factors.Generically these include more thanmicrobes, chemicals, or nutrients, but alsoanthropometric, physiological and geneticfeatures as well as behaviors, mental states,

race and socioeconomic status. The methodof the discipline is to observe whether diseaseoccurs more (or less) commonly among indi-viduals who have the exposure or factor thanthose who do not. The broader goal of expla-nation of the occurrence of disease in popula-tions is pursued by enumerating all the riskand protective factors (the "independent vari-ables") and the form of their relationshipswith a list of disease outcomes derived pri-marily from clinical practice (the "dependentvariables"). The results of this research can berecognized in the lists of carcinogens, cardio-vascular risk factors, and health risk behav-iors that are target ed for modification byhygienic, behavioral or pharmacologicalintervention.

Studying Disease in PopulationsBefore going further it may be helpful to

clarify what is meant when it is said that epi-demiology is the study of disease in popula-tions. The populations of modern epidemiol-ogy are counts -- numbers of individuals --who are grouped according to their exposureand disease status. Populations, in this con-text, are vehicles for making comparisons ofrates or averages; they are not inherentlydefined as organized groups with unique his-tories involving economic, social and ecolog-ical relationships. Their features of organiza-tion, in the epidemiological context, are notconsidered to have etiological consequences.Epidemiological studies that do address fac-tors such as economic position or occupationgenerally treat them only as individual attrib-utes or exposure markers rather than asaspects of social and economic organizationthat provide the context for biopsychosocialdevelopment. Thus race, as a feature of indi-viduals, can be studied without recognizing

Limits of Epidemiology Wing 75

racism as an historical feature of the organi-zation of populations. Epidemiological stud-ies labeled as "ecological" examine associa-tions between average levels of exposure anddisease in groups [6,7], not population orga-nization and ecological relationships [8,9].

The view that disease in populations is afunction of essential exposure-disease rela-tionships is mirrored in the model for mod-ern epidemiological study designs, the ran-domized experiment. In this approach, sub-jects with specific characteristics, includingabsence of a disease or outcome of interest,can be chosen for study. Next they can beallocated to be exposed or unexposed to afactor according to rules that, as in the well-shuffled decks of repeated card games, tendtowards an even distribution of the heteroge-neous study subjects between exposuregroups over the course of many trials. Duringthe period of application of controlledamounts of exposure (or non-exposure), allother conditions affecting the subjects can beheld constant. Finally, the subjects are avail-able to the researcher for determination of theoutcome characteristics in members of eachgroup, using a standardized protocol. Theanalysis of such a study amounts to a com-parison of the frequency of the outcomes ofinterest in the groups. Differences in frequen-cy that persist over many trials, or that areobtained in a small number of large trials, areattributed to the action of the experimentalagent. It should be clear that any questions ofcontext, such as where the exposures havecome from, why some individuals but notothers were exposed, or what other changesoccurred in order to produce the exposures,have been eliminated from the realm of sci-entific interest.

Observational studies attempt to imitatethe controlled experiment in various ways.An occupational study of the effects ofgamma radiation on cancer might be restrict-ed to workers of a certain type (e.g., malesemployed at a specific facility who workedlonger than six months) to avoid some initialdifferences between exposure groups, andmight compare workers that had receiveddifferent cumulative radiation exposureswithin strata of age, other occupational expo-sures, and behavioral attributes of interest, toprovide a summary estimate of the exposure-disease relationship "adjusted" for thoseother factors. In attempting to yield resultsthat would have been obtained in an experi-ment, the observational study controls "extra-neous" factors (and the context) in search ofthe separate, independent effect of the expo-sure. The assumption is that well-designedstudies will provide estimates of the radia-tion-cancer dose response relationship thatconverge around the underlying value whichcharacterizes the change in cancer rates foreach unit change in radiation.

Problems in EpidemiologicalExplanation

Problems in epidemiological explana-tion can be approached from two related per-spectives. This section addresses logicalproblems with the object of investigation ofmodem epidemiology, exposure-diseaseassociations, and with interpretation of evi-dence about associations. Later sectionsaddress problems with the nature of the pub-lic health impact of the application of thisknowledge. Problems in interpretation ofexposure-disease associations receive greatattention in the epidemiological literature.This attention is primarily focused on issuesof measurement error and uncontrolled dif-ferences between groups being compared,issues that create difficulties because themagnitude and dose response form ofobserved associations may reflect thesesources of bias rather than the association ofinterest. Despite these ambiguities, muchrefinement of method has occurred, andmodern epidemiology has contributed to theidentification of many pathogenic agents.Some, like cigarette smoke, produce largeeffects that are hard to miss. Others, likeasbestos, have specific effects (mesothelioma)that rarely occur in the absence of the expo-sure. Much of epidemiology today, however,is focused on a search for evidence aboutweaker relationships and low exposure lev-els, where poor measurement and the pres-ence of unmeasured differences betweenexpo sure groups become major potentialproblems [10]. Relatively small differences in


disease occurrence, such as those that are sus-pected in the case of low level radiation andmany other environmental contaminants, aredifficult to detect because very accurate mea-surements are necessary for quantifyingexposures and disease excesses that are notfar above the "background" levels. But smallincrements in disease incidence can have agreat population impact when many peopleare exposed (Fig 2) [11].

What Should be Measured? A more fundamental problem in epi-

demiological explanation is the developmentof theory about which aspects of exposureand outcome to measure. Outcomes general-ly reflect experience with diagnosis and treat-ment more than with etiological inquiry.Exposures are often measured due to conve-nience, availability of data, or convention,rather than based on biological models of dis-ease process. Among workers exposed topenetrating ionizing radiation over long peri-ods, for example, the total cumulative dose(derived by applying assumptions about rel-ative biological effectiveness to measures ofbiologically absorbed radiation of differenttypes) is typically studied. Sometimes onlythe doses received up to a certain number ofyears in the past are counted, on the assump-tion that cancers take time to develop.Alternatively, doses received in the distantpast might not be relevant, and the doses thatshould be counted might only be those accu-mulated in some window of time around theemergence of the hypothetical mutation lead-ing to a particular cancer death [12,13]. Thenagain, it might not be the simple cumulativedose that is critical, but whether the dose isdelivered in one or a few short time periods,or is drawn out slowly. Other possibleaspects of radiation exposure that might beimportant to measure are the peak dose, orthe dose accrued in the context of other cocar-cinogenic exposures or susceptibility states.Lack of understanding about mechanisms ofradiocarcinogenesis means that problems ofmeasurement are secondary to the more fun-damental problem of knowing what to mea-sure [14].

Like problems of measurement andcomparability, questions about the biomed-ical basis for modeling exposure-diseaseassociations are of concern within modernepidemiology [e.g., 2,15]. The former techni-cal concerns lead investigation in the field toemphasize increasing control over measure-ment and extraneous factors that can distortthe exposure-disease association, while con-cerns over the latter conceptual issues focusthe discipline's theoretical attention onpathological processes of individual organ-

isms. Because control over measurement andextraneous factors is hindered when investi-gations are embedded in complex social andhistorical situations, this combination ofinfluences supports the movement of the dis-cipline away from engagement with issues ofsocial theory, population biology and humanecology, and towards a more fundamentalcommitment to bio medical approaches.

The Broader Context of Exposure-Disease Associations

This direction is justified on the assump-tion that it will lead to the more accuratedescription of the underlying exposure-dis-ease relationships that account for health anddisease in populations. These relationshipsare seen as being self-contained, homoge-neous, and independent phenomena. Theyare therefore appropriately studied in isola-tion, one at a time, according to the approachformalized in the experiment, in order tomove "from time- and place specific observa-tions to an abstract universal statement" [2, p96]. In this approach, the experiences of par-ticular populations "are only exploited tolearn about the relation at issue in theabstract (in general), that is, without any spa-tiotemporal referent" [3, p 16]. Thus, modernepidemiology is oriented towards identifyingthe fundamental laws, not of the universe,but of exposure-disease associations.

The idea that epidemiology is about uni-versal exposure-disease associations may cre-ate some discomfort, at least because epi-demiologists presumably believe that biolog-ical organisms evolve and therefore are nothistorically constant vehicles for suchprocesses. From a more contemporary per-spective, it is already recognized in epidemi-ology that exposure-disease associations varybetween different groups depending on hostcharacteristics or other exposures. This varia-tion, often called interaction or effect modifi-cation, raises important questions about theunderlying phenomenon being investigated.For strong exposure-disease relationships,such as smoking and lung cancer, effect mod-ification may be of minor interest. In somecases, however, and especially for low levelexposures, variations in exposure-diseaseassociations under different conditions maymake the difference between no relationshipand an important one. For ionizing radiation,it is recognized that associations may bemodified according to age of exposure, sex,and perhaps other factors including diet,presence of other chemicals, and geneticcharacteristics. On the other side of the expo-sure-disease equations, disease categories areinevitably heterogeneous, with the associa-tion of exposure and disease showing more


or less variability for subgroups of broad dis-ease categories used in epidemiological stud-ies. For example, among A-bomb survivors,radiation is related to neoplasms, to solidtumors, and to leukemias in general, but tosome types of each more than others [16]. Weare always studying average effects.

In epidemiological practice, while effectmodification is recognized, it is treated as aspecial case, a sub-class of universal associa-tions that is "an inherent characteristic . . . anunalterable fact of nature" [17, p 586]. This sta-tus preserves the logical commitment tomethods and theories predicated on thesearch for self-contained independent rela-tionships that are, if not completely universal,at least homogeneous within subgroups. Thebelief in independent exposure-disease rela-tionships leads to the centrality of the issue ofcontrolling confounding bias through designand analysis. But there remains an uneasycontradiction within the field between, on theone hand, expanding epidemiologicalresearch (traditionally limited to middle-agedwhite men) to include women, non whites orthe elderly, because of potential variation inexposure-disease relationships, and, on theother hand, the interest in techniques forquantitatively combining results from differ-ent studies [18] in order to produce a morereliable estimate of an exposure disease asso-ciation based on the assumption that differentstudies of the same exposure-disease relationship are providing estimates of a universalunderlying phenomenon.

Contextual ComplicationsAlthough some relationships may be

fairly stable over a large range of contempo-rary contextual variation (this is argued bysome, for example, in the case of serum cho-lesterol and coronary disease in adult males),change in biological response to exposureshould be expected on longer evolutionarytime scales. The view that exposure-diseaseassociations generally vary with context sug-gests that there is no underlying universaldose response relationship to be uncovered[19]. Rather, for any given exposure and out-come, there is some range of contexts inwhich the change in outcome per unit changein exposure exhibits more or less stability.From this perspective the fundamental objectof inquiry in modern epidemiology, doseresponse, should be recognized as essentiallycontextual (developmental or historical)rather than universal, vastly complicating thereductionist program and, indeed, challeng-ing the very de-contextualization on which itis based.

Description of the quantitative impact ofdisease agents is important, has practical

implications, and should continue to be a partof epidemiology. The practical importance ofthe activity, however, does not mean that thestudy of exposure-disease associations consti-tutes a sufficient or rigorous object of inquiryfor a basic science of public health. This is sobecause the object of inquiry itself, the expo-sure disease association, is not a self-con-tained, homogeneous, or independent phe-nomenon as presumed by the approach thattreats the experiment as a "paradigm" forresearch [20]. This approach has been calledmodern epidemiology [2], analytical epidemi-ology [21], occurrence research [3], and riskfactor epidemiology [22, 23]. It is essentially akind of human toxicology, an approach limit-ed to the identification of risk factors using ananalytical approach in which the historicalcontext is a nuisance to be avoided by designor controlled by analysis. Such an approachjustifies conclusions of leading methodologistsin the field that war and epidemics are notproblems for epidemiology [3, pp 4-5], andthat "social class is presumably causally relat-ed to few if any diseases" [2, p 90] because it isonly agents or risk factors, not characteristicsof the organization of populations, that are eli-gible to be causes of disease. This limitation ofcausal explanation to the pathogenic action ofrisk factors in individual organisms is codifiedin the lists of "criteria for establishing causali-ty" rehearsed in textbooks and journals [e.g., 2,21, 24].

Expanding EpidemiologyModern epidemiology can be contrasted

with perspectives that recognize the roles ofspecific exposures but that place these expo-sures in a context that is itself of interest inscientific explanation and public health inter-vention, an approach closer to human ecolo-gy than to human toxicology [25]. Examplesof broader views of the scope and goals ofepidemiology can be found throughout itshistory. The mid 19th-century work of theyoung Rudolf Virchow has been revived asan early example of a quantitative approachto understanding disease in populations that,while recognizing the importance of specificagents or exposures, did not reduce theexplanation of disease to a matter of theseisolated factors themselves [26-28]. Virchow,in investigating an epidemic of typhus inSilesia, was deeply moved by the suffering ofthe people, and his explanations stressed theconditions that fostered the epidemic: lack ofagricultural land, malnutrition, poor hous-ing, low wages, and language barriers for thelarge Polish minority. His report to the gov-ernment advocated land reform, progressivetaxation, establishment of agricultural com-munes, local political autonomy, and, lastly,


creation of a system of public hospitals.Virchow's conclusion: "Medicine is a socialscience, and politics nothing but medicine ona grand scale" [26, 27].

Pioneers of a New EpidemiologyOther l9th century research that did not

exclude the context of exposures was done inFrance [29] and England. The public healthresearch that Friedrich Engels conducted inEngland was particularly insightful [26]. Hedocumented the health problems that arosefrom crowding, lack of sanitation, malnutri-tion, and abuse of alcohol to alleviate chronicpain. Like Virchow, he quantified excesses ofdisease and death through statistical studywithout naming the analyzed factors, be theyoccupational, nutritional or behavioral, as theautonomous causes of disease. UnlikeVirchow, however, Engels did not believethat reform of the political system would evercreate the underlying conditions for adequatepublic health. Rather, he identified the capi-talist economic system itself as the source ofill health. Increasingly reductionist epidemi-ological thinking emerged in the context ofPasteur's discovery of microbes, the develop-ment of a more effective (and less damaging)allopathic medical practice, and the increas-ing dominance of statistics in quantitativeinvestigation. Not all epidemiology, howev-er, was converted to the theory that so suc-cessfully reduced the cause of disease to agerm, simultaneously distracting attentionfrom the material living and working condi-tions in which disease arose. During the1920s Joseph Goldberger showed that pella-gra was not an infectious disease, as many atthe time thought, that it was related to nutri-tional deficiency, and that its occurrence inthe U.S. South depended on a share-croppingsystem that locked large numbers of peoplein poverty [30]. Unfortunately, his more glob-al analysis of the economic arrangements inwhich pellagra and other public health prob-lems proliferated was ignored by policy mak-ers in favor of supplementing flour withniacin, a solution that probably contributed(along with access to electricity, refrigerationand dietary improvements) to the reductionof pellagra, but left in place the rural South'sunderdeveloped economic circumstancesthat continue to make the region the locationof some of the worst public health conditionsin the U.S. Yet Goldberger's well documentedresearch strategies can help contribute totoday's critical evaluation of methodology inthe field.

More holistic approaches to epidemiolo-gy continued in some third world countries.In Chile, the physician Salvador Allendecame to believe that he would make the

greatest contribution to the health of his peo-ple not by treating patients one at a time, butby working against the devastating effects ofunder development [26]. As president ofChile, he realized Virchow's vision of politicsas medicine on a grand scale. Latin America -- where it is clear that the immediate publichealth problems of disease in populationshave less to do with specific exposures thanwith a position in the international economicsystem that sustains a lack of decent jobs,housing, clean water, food, and democraticcontrol of institutions -- is now home to anumber of alternative currents of develop-ment in epidemiology. In these circum-stances it is difficult to sustain the first worldmirage that substantial public healthadvances can be achieved through the enu-meration and regulation of unhealthy expo-sures on a case-by-case basis.

Pressure for change in epidemiologyalso comes from groups that have beenexploited on the basis of race, gender andclass, and from environmental and peaceactivists. One aspect of an expanded publichealth agenda that is drawing attention fromofficial agencies and academics in the U.S. isenvironmental racism [31,32]. Increasingly,studies are documenting the systematic pref-erential location of toxic waste sites and pol-luting industries in areas that are predomi-nantly inhabited by people of color and thepoor (Fig 3). The primary issues here are notthe identification of specific chemicals associ-ated with particular diseases, threshold expo-sures for health effects, or dose response esti-mates; rather, the generation of exposures orpotential exposures, environmental equity,and democratic decision-making are of pri-mary concern. The specific effects of contam-inants as well as medical means for treatingproblems once they occur are of great interest


and importance, but as those issues areviewed in a larger context, they can poten-tially be connected to other health problemsand the development of coordinated solu-tions. Thus, contamination of NativeAmerican lands in the south western U.S. byuranium mine tailings, nuclear weapons test-ing, and radioactive waste disposal can beconnected to the long history of expropria-tion and destruction of Native lands, ecosys-tems, and means of subsistence, which havedevastated Native public health for centuries.

Application of Epidemiology toPublic Health

Epidemiology as a basic science of pub-lic health affects the nature of public healthinterventions. Because of its declared objectof inquiry, modern epidemiology generallyleads to interventions directed at specificindividual exposures, and it is thereforeimportant to consider the consequences oftrying to intervene on specific exposure-dis-ease associations in isolation from their con-text. Before addressing radiation and health,let us consider smoking and health, a text-book example of the early application ofmodern epidemiology for which publichealth consequences can be evaluated overthree decades.

Despite widespread clinical observationsof smokers' symptoms and the physical andbiological plausibility of smoke as a lungpathogen and carcinogen, it was evidencefrom epidemiological studies of the 1940s and1950s that led, in the United States, to theSurgeon General's 1964 report on the healthhazards of smoking [33]. Modern non-infec-tious disease epidemiology had its first majorsuccess in identifying associations betweencigarette smoking and lung cancer and otherprominent diseases. Subsequently, publichealth efforts were initiated to reduce theprevalence of smoking through educationabout smoking hazards and through control ofcigarette advertising. Over the last threedecades there has been a remarkable shift inthe prevalence of smoking and the burden ofsmoking-related diseases, a shift that can beattributed in part to the epidemiological expla-nation of the cause of smoking-related dis-eases. Smoking prevalence has declined sub-stantially among better educated, higherincome people in North America, parts ofWestern Europe, Australia and New Zealand[34]. Smoking prevalence has declined little ornone among lower educated and lower incomepeople in those countries [35], and is increasingrapidly in many of the most populous parts ofthe world [36]. Thus in the three decades fol-lowing epidemiology's major success, morepeople are exposed to and made sick from thedisease agent than ever before [37].

Tobacco and EpidemiologyThe populations studied by modern epi-

demiologists were the exposed and the unex-posed defined by the model of the experi-ment. They were not highly organizedgroups with economic systems and socialrelations. Thus, the cause of the lung cancerepidemic was identified as cigarette smoking,an individual behavior, while tobaccoagribusiness, the commercial sale of ciga-rettes, and the social circumstances that make


smoking a rewarding habit, could not be rec-ognized by epidemiological studies as targetsfor intervention. When educational effortsand social options led some groups to reducesmoking levels, tobacco companies redirect-ed advertising to replace those markets withothers, often assisted by governments withtheir own financial stakes in tax revenues andcontributions to trade balances (Fig 4) [38].

Not only has the identification of theassociation between smoking and diseasefailed to stem the world-wide epidemic ofsmoking-related diseases, it has redistributedsmoking prevalence so that it increasinglyadds to inequalities in health between thepoor and the rich within countries of theNorth [39], and between countries of theNorth and the South [40]. Such redistribu-tions may be expected when interventionsare directed only towards consumptionrather than towards both production andconsumption [41], and it is only the behaviorof consuming cigarettes, not the organizedproduction and promotion of tobacco, thathas been considered by epidemiologicalstudies. Health inequalities are further exac-erbated through replacement of local foodcrops by tobacco for commercial markets andby toxic exposure of industrial and agricul-tural workers during manufacture and appli-cation of agricultural chemicals.

Three Sources of RadiationExposure

A related situation can be describedwith radiation and health. The problem asnow defined in the terms of modern epi-demiology is one of quantifying the extent ofthe increase in cancer (or birth defects orsome other physiological or disease outcome)produced by every unit increase in an indi-vidual's dose of ionizing radiation. The accu-rate quantification of this relationship willsupposedly provide the basis for the rationaldetermination of how much radiation expo-sure would be permissible, and regulationswould be designed accordingly. As in thecase of the evaluation of smoking and health,the situation of an individual's exposure isseparated from the context of the productionof the exposure and the other effects of thatproduction on health and society.

Most manufactured exposures to radia-tion take place within the context of the ener-gy, military, and medical industries. The mil-itary industry, which has produced many ofthe exposures studied by epidemiologists,developed in support of the creation of tensof thousands of nuclear weapons (Fig 5).Nuclear proliferation and the threat of cata-strophic nuclear war continue. Attempts toclean up the most toxic remains of this pro-

duction are just beginning, will go on fordecades if not centuries, and cannot possiblyrestore many areas to safe states.

The history of environmental contami-nation and human suffering in areas used forproduction and testing is horrible, and thestories of the affected people and places areindeed chilling [42,43]. The public health con-sequences of direct contamination, however,are only a small part of the much largerhealth impact of the exposure context, theindustry without which the exposures wouldnot have occurred. This military enterpriseand the research infrastructure that supportsit have used huge proportions of nationalbudgets and engaged hundreds of thousandsof people in activities that have as their mainpurpose not social welfare, but developmentof means of destruction, diverting humanand economic resources from potential pro-jects to improve living conditions throughoutthe world. The expense and sophistication ofnuclear technology itself has generated a sci-entific and bureaucratic elite that has perpet-uated itself through secrecy, concentration ofpower, and elaboration of a xenophobic anddivisive brand of patriotism [44]. This socialcontext is highly undemocratic and con-tributes to inequalities of wealth and powerjustified on the basis of special knowledge ofan elite group that is supposedly uniquelyqualified to make decisions, promoting disre-gard for protection and rights of workers,indigenous peoples and others that areexcluded from participation in decisionsaffecting health conditions.

The Health Effects of Industries andSocial Policies

The use of nuclear technology for powerproduction could not have occurred withoutthe support of the infrastructure and researchbase created for military purposes. Once thecommitment had been made, however, thecommercial industry contributed to the hopesfor ever-increasing energy consumption withthe promise of a clean and cheap source ofpower. The industry proliferated widely in theabsence of political and technical solutions tothe problems of waste disposal. Energy wouldbe produced without limit in centralized loca-tions controlled by a technical elite rather thanwith a technology that could be widely dis-tributed and controlled more democratically.This vision of electric power generation has inpart prevented the development of a policyalternative to unlimited growth that is ecolog-ically sound, sustainable, equitable, and con-sistent with reduced inequalities in healthbetween the majority of the world's peoplethat use little energy and the minority thatconsumes most of the energy.


Medical uses of ionizing radiation pre-ceded the military and energy uses bydecades, and while there have been impor-tant diagnostic and therapeutic applications,many disasters and victims were created inthe process [44]. These include patients sub-jected to x-ray and radium treatments, chil-dren exposed to x rays during pregnancy,and many of the clinicians that treated them.In medicine, consideration of the context ofradiation exposures could encourage greaterattention to preventive rather than diagnosticand curative measures, and, within the con-text of the latter, could draw attention tooveruse of tests and treatments with margin-al benefits.

In all three radiation industries, the exis-tence of a technology that proponents pushedas a quick fix for complex social problems --international conflict, energy policy andmedical care encouraged the attitude that itwould not be necessary to address the globalissues of political relationships, ecologicalsustainability, disease prevention andhumane healing, but only to put faith in atechnology that would provide the power tosolve what was perceived to be a specificproblem by itself. The health effects of thesepolicies occur not only through agents likeionizing radiation, but more importantlythrough their effects on society, on socialinequalities, and on living conditions that areessential to public health.

Smoking and health and radiation andhealth are only two examples of how thenature and object of epidemiological explana-tion limits its scientific scope and publichealth application. Similarly, a focus on high-fat diet as individual behavior fails to addressconsequences of the animal-oriented agricul-ture systems that support mass high-fat diets.These consequences include production ofexport crops in the context of local malnutri-tion, use of vast quantities of non-renewableenergy resources, occupational expo sure topesticides and herbicides, topsoil loss, andgeneration of methane greenhouse gases.

Two responses to this situation are sug-gested by approaches reviewed above. One isthat epidemiology is simply not about thesebroader issues, rather, they are the responsi-bility of other disciplines. Another is that epi-demiology has addressed the broader issuesof context in the past, and that it has only lostthat ability and interest because of the eco-nomic and political context of its dominantmodern practice. Epidemiology is not aloneamong disciplines in its reductionism, and itcannot carry the burden, by itself, of adopt-ing an ecological perspective. Rather, allhealth-related disciplines should adopt abroader perspective within their particular

practice, encompassing and transforming theconcepts and tools that have developed ineach area.

Scientific Objectivity and SocialResponsibility

Many scientifically trained people, aswell as non scientists who have felt comfort-able putting their faith in the experts, havebeen attracted to reductionist science becauseof the very characteristics criticized here.According to this logic, it is only by exclud-ing the context and focusing on particularfactors considered independently of histori-cal conditions that science can produce objec-tive knowledge that has a greater claim toauthority than other forms of knowledge.Although this perspective continues to thrivein the biomedical sciences, including epi-demiology, it has been thoroughly critiquedby historians, philosophers, and practitionersof science of the latter half of the twentiethcentury [5, 45-52].

Science and ConceptualFrameworks

The basis of the critique of value-freeobjectivity is simple: it is impossible to knowthe world without intellectual tools, includ-ing languages and socially produced con-cepts. Whether explicit or not, all scientificinvestigations depend on conceptual frameworks. There can be no unmediated experi-ence. These ideas have been extensivelydeveloped in various directions by manyauthors, especially since the seminal work ofThomas Kuhn [45], and they provide a basisfor the most fundamental challenge to reduc-tionist epidemiology by removing its justifi-cation as a unique means to provide objectiveanalyses of health and disease problems. Thechoice is not between objective science and ascience that is contaminated by social andpolitical values. Risk factor epidemiologydoes not achieve objectivity by systematicallyexamining exposure disease associations sep-arated from contexts of military, energy, oragriculture policy, and issues of economicinequalities and democracy. Rather, it makesa political commitment to the status quo byexcluding these issues from public healthconsideration.

Shattering the myth that scientificinquiry can be independent of societyamounts to recognizing the "distinctionbetween the claim that the world is out thereand the claim that truth is out there" [53].Belief that truth is something which is found"out there" rather than something that ismade from observations of the world usingsocially and culturally produced languagesand concepts is partly a reaction to the mis-


taken perception that the only alternative tovalue-free scientific objectivity is relativismand the abandonment of any basis for mak-ing comparative evaluations of scientificexplanations. But recognition that all knowl-edge, including scientific knowledge, is root-ed in social constructs does not negate theidea of objectivity in the sense of fairness, jus-tice, and intellectual honesty. This has beencalled "strong objectivity" by Sandra Harding[46], a concept that she has counterpoised tothe "weak objectivity" perpetuated by practi-tioners of Cartesian reductionism. Strongobjectivity depends on explicating assump-tions and goals through self critique ratherthan denying them by constructing a myth ofsocially unmediated scientific experience.Consideration of social responsibility as partof an analysis of the construction of scientificknowledge is therefore not something to betacked on to scientific practice after the fact,but is a necessary part of being objective inthe sense of being explicit about assump-tions. The development of an alternative toreductionist epidemiology depends on such acommitment.

Recognizing social responsibility as anintegral part of scientific inquiry, however,forces us to make judgments about socialresponsibility, an ethical dilemma that isdenied by those who believe that objectivityis obtained by separating science fromhuman values. What, then, is to be the basisof moral judgment, and how are conflictsbetween different cultures and classes to beresolved? Most philosophical approachesconsider this question against the standard"that there must be necessary, universalgrounds for all moral principles" [54, p 9],either searching to establish the basis forthese universal grounds or accepting a defen-sive posture of moral relativism. PhilosopherCornel West argues that the search for uni-versal moral certainty is doomed, but thatvarious brands of moral relativism are unac-ceptable. He dissolves the problem of choos-ing between universal and relative moralprinciples by substituting a historical basis ofthinking about morality which holds "thatthere are moral truths or facts, but that theyare always subject to revision . . .relative tospecific aims, goals, or objectives of particulargroups, communities, cultures, or societies"[55, p 10]. West calls for "a historical assess-ment and political reading of our moralityand morale, in order to shed light on how wecan make them more contagious to otherscaptive to the prevailing cynicism andnihilism [of our culture]" [55, p xiii]. Such anethical position can support a sociallyresponsible scientific practice but requiresfull engagement with, rather than denial of,

the ethical aspects of the social constructionof scientific knowledge.

An Alternative EpidemiologyIf we accept a broad critique of the dom-

inant practice of epidemiology, as opposed tothe view that the discipline is essentially ontrack but needs fine tuning, the first questionthat arises is, "If this isn't the right way to doit, then what do you propose?" The answer tothis question must emerge through the devel-oping work of diverse groups of researchersand practitioners who are struggling to makethe field more relevant to improving publichealth conditions throughout the world.There are many examples in the current liter-ature of attempts to work out more or lesscontextual explanations of health and diseasephenomena [5, 8, 9, 11, 25, 47, 51, 56-58],although they are not yet connected in acoherent set of theories, assumptions andtechniques that could constitute a real newparadigm [see 59 for a discussion of compet-ing paradigms in epidemiology].

An alternative practice that is shared bylarge numbers of scientists will no doubtrequire much time and larger scientific, socialand political change. Such change will beaffected by relationships between profession-al practices including medicine and publichealth, and broader based efforts to improvepublic health conditions, including civilrights, economic justice, environmental, anti-war, and other activities. Epidemiology isalready being affected by involvement ofnon-professionals with new ideas aboutappropriate research questions, evidence,and interpretations of findings [60].

How would such an epidemiology bepracticed, and what would its products looklike? First, it would not just ask questionsabout what is good or bad for health in gen-eral, but it would analyze differential effects -- good or bad for whom? Second, it wouldlook for connections between many diseasesand exposures, what is common about them,instead of always isolating exposure-diseasepairs. Third, it would look for side effects ofinterventions and exposures, the unintendedconsequences that may be more importantthan the intended ones. Fourth, it woulddevelop ways to utilize historical informa-tion, the developmental narratives of particu-lar populations and even individual people,with the aim of connecting the particular andthe general. Fifth, it would address the con-ceptual framework of the research, includinganalysis of assumptions and the social con-struction of scientific knowledge, as a centralpart of any research reporting, as central to aresearch manu script as consideration ofmeasurement error or selection bias [49].


Sixth, such an epidemiology would recognizethat the problem of controlling confoundingfactors comes from the search for indepen-dent relationships, not from the world westudy, and that the "nuisance factors" of thereductionist perspective can become theessential context of exposure and disease ofan ecological perspective. Finally, it wouldentail a humility about the scientific researchprocess and an unrelenting commitment toplaying a supportive role in larger efforts toimprove society and public health.

Efforts to articulate an alternative epi-demiology are connected by attention to thehistorical contexts of public health phenome-na as well as to the science that addressesthem. These positions are contrary to thedominant assumptions that there can be anahistorical, value-free epidemiology that isabout ahistorical, independent exposure-dis-ease associations. Research into the healtheffects of ionizing radiation is a stereotypicalexample of the application of the reductionistprogram, preoccupied as it has been with thesearch for the shape and magnitude of a pre-sumably universal dose response relation-ship and its consistency across populations,and the quest for an ahistorical constant thatwill be analogous to the fundamental laws ofnature supposedly uncovered by the disci-pline that produced the exposures understudy, physics. Meanwhile, the public healthdisasters of runaway military spending,uncontrolled energy consumption, and dom-inance of high-technology curative medicineover preventive environmental and medicalpractices, go unseen by the "basic science ofpublic health."

Our dominant epidemiology beginswith the assumption that things work sepa-rately and independently, that exposures canbe separated from the practices that producethem. An epidemiology oriented towardsmassive and equitable public healthimprovement requires reconstructing theconnections between disease agents and theircontexts. This is necessary for the successfulapplication of scientific knowledge to publichealth practice, for the resolution ofintractable technical and conceptual prob-lems inherent in current exposure-diseasestudies, and for the development of a sociallyresponsible epidemiology. The practical,technical, theoretical, and ethical goals arecomplementary. Such a direction will allowus to recognize the health consequences ofindustries and social and economic arrange-ments as well as the roles of specific diseaseagents. As social, economic and politicalarrangements that provide the conditions forpublic health and human developmentbecome an explicit part of the epidemiologi-

cal explanation of health and disease in pop-ulations, efforts to oppose injustice and inhu-manity can be recognized as an integral partof a comprehensive public health agenda.Current global public health crises demandmore than a piecemeal approach.

AcknowledgmentsInstitutional and intellectual support

was provided by the Department ofPreventive Medicine, Federal University ofBahia, Salvador, Brazil, and the BrazilianNational Research Council. I am grateful tothe many colleagues and friends who provid-ed input on earlier drafts. Rudi Nussbaumwas instrumental in encouraging me to writethis paper.

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