EMF and Cancer Kheifets et al. Electric and Magnetic Fields and Cancer: Case Study

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1 American Journal of Epidemiology Copyright 2001 by the Johns Hopkins University Bloomberg School of Public Health All rights reserved Vol. 154, No. 12, Supplement Printed in U.S.A. EMF and Cancer Kheifets et al. Electric and Magnetic Fields and Cancer: Case Study Leeka I. Kheifets, 1 Raymond S. Greenberg, 2 Raymond R. Neutra, 3 Gordon L. Hester, 1 Charles L. Poole, 4 David P. Rall, 5 and Gail Lundell 1 Electric and magnetic fields (EMF) are produced when electric power is generated, transmitted, and used. Concerns about whether EMF could adversely affect human health were raised initially by epidemiologic studies reported in the late 1970s, and since the 1980s, findings on EMF have been widely publicized in the popular press. Epidemiologic studies have examined both occupational and residential EMF exposures, focusing on residential exposure and childhood cancers, but also extending to breast and other cancers in adults particularly for occupational exposures. More recently, and since this case study was prepared, concern has broadened to EMF from cellular telephones. Interpretation of the epidemiologic data has been difficult. Although positive associations have been observed in some studies, relative risks have been small, and the studies generally have lacked statistical power. Also, results have varied according to the method used to estimate residential exposure, making interpretation of the evidence difficult. Biologic mechanisms by which EMF could cause cancer have been uncertain, although hypotheses have been offered, such as the hypothesis that EMF may increase the risk of breast cancer by reducing melatonin levels (1). Studies in laboratory animals have been largely negative (2). In vitro studies have indicated that EMF exposure can induce biologic responses; however, replication of most of this work has proven to be extremely difficult. Furthermore, the relevance of the responses observed in in vitro systems to cancer development is unclear. Exposure to EMF does not initiate steps in established mechanisms of carcinogenesis, such as damage to DNA (2). The question of risk of cancer from EMF exposure thus remains controversial despite more than two decades of research and multiple reviews by expert scientific panels. The continued concern stems largely from observational studies. Received for publication December 27, 2000 and accepted for publication September 4, Abbreviation: EMF, electric and magnetic fields. 1 The Electric Power Research Institute, Palo Alto, CA. 2 Department of Biometry and Epidemiology, Medical University of South Carolina, Charleston, SC. 3 Division of Environmental and Occupational Disease Control, California Department of Health Services, Oakland, CA. 4 Department of Epidemiology, University of North Carolina, Chapel Hill, NC. 5 Deceased. Reprint requests to Dr. Leeka Kheifets, World Health Organization, Occupational and Environmental Health, Protection of the Human Environment, 20 Avenue Appia, CH-1211 Geneva 27, Switzerland ( kheifetsl@who.int). Epidemiologic research on the possible relation between EMF and risk of cancer was selected as a case study for several reasons. Though the magnitude of the reported exposure-disease association has been small and at the limit of detection of epidemiologic methods, the ubiquity of EMF exposure could nonetheless lead to an appreciable public health impact. Also, public concern about EMF has been high. The invisible and involuntary nature of EMF exposure, its presence within the sanctity of the home, and the putative health outcome of cancer, particularly leukemia, among children have all heightened public anxiety. Consequently, media coverage has been intense and the issue has been brought to a wide public awareness. In a 1997 survey of public opinion cited in Scientific American, onethird of the public said they were convinced that EMF posed some degree of hazard (3). EMF as a potential health hazard is also relevant as a case study because of controversy within the scientific community. Some investigators outside the field of epidemiology have stated that EMF cannot be expected to lead to cancer or any other effect (4). A commentary in the periodical Science highlighted EMF studies as a prototype of the limitations of modern epidemiology (5), leading some commentators to conclude that the evidence on EMF is little more than junk science (6). Even within the epidemiologic community, findings have received varying interpretations because of methodological problems, particularly those related to exposure classification, as well as questions about physical and biologic plausibility. Also, because the initial studies were conducted by non-epidemiologists and newcomers to the field, their credibility may have been compromised. Government responses to the EMF issue have been highly variable. Federal funding for research in the United States has fluctuated, hindering sustained scientific investigation. The Swedish government, by contrast, has provided a steady stream of funds. In the regulatory arena, Sweden was quick to implement prudent avoidance strategies to limit public exposure; the United States has followed a more restrained approach, waiting for greater consensus from scientists and risk assessors before taking a stance. Most court decisions in US tort cases have not accepted that a cause-effect relation between EMF exposure and disease has been established. The ongoing saga of EMF represents an illustrative case study of the interplay between and within different scientific disciplines and between epidemiologists, the popular media, and regulatory agencies. The case study begins with historical background, continues with an examination of the role of epidemiologic and EMF-specific issues in policy- S50

2 EMF and Cancer S51 making, and concludes with a discussion on communication, essential to the interaction between epidemiology and policy. Readers of this case study should recognize that it is largely based on publications and events through the late 1990s. It is not intended to be a comprehensive, up-to-date literature review, nor is it an attempt to evaluate the evidence on EMF and risk to health. HISTORICAL BACKGROUND Table 1 presents a synopsis of some of the important scientific findings and policy actions over the 30-year history of the EMF debate. Public concern over power-frequency electric and magnetic fields first arose in the early 1970s with reports from the Soviet Union that workers in extrahigh-voltage switchyards suffered from a broad range of nonspecific symptoms (7). In the United States, concern about potential health effects became a central issue in the siting of transmission lines. Consequently, the New York Power Lines Project, a research program to study proposed power lines, was developed under mandate from the New York State Public Utility Commission. The US Department of Energy and the Electric Power Research Institute also initiated research programs to study the biologic effects of electric fields. In the late 1970s and early 1980s, several published studies further fueled concern over EMF. The reported higher rates of cancer mortality in children living near high current configuration power lines (8), higher leukemia rates in electrical workers (9), and the possible teratologic effects found in an animal study (10) gave impetus for the US Environmental Protection Agency to request, in 1984, that the National Council on Radiation Protection and Measurements review the issue of potential health effects of power-frequency EMF exposure. Although information from the draft of the National Council on Radiation Protection and Measurements report was leaked to the press (40, 41), the official report is yet to be published. A US Office of Technology Assessment report, published in 1989 (13), suggested prudent avoidance as a policy option. Prudent avoidance was defined as taking steps to keep people out of fields both by rerouting facilities and redesigning electrical systems and appliances ; prudence meant undertaking only those avoidance activities which carry modest costs. In addition, a series of articles by Paul Brodeur in The New Yorker (14 16) thrust the EMF issue into the public and popular media arenas. Brodeur voiced a strong opinion that EMF caused cancer and suggested a cover-up, dismissing scientists who urged cautious interpretation of data and more research. In December 1990, the US Environmental Protection Agency released a draft report concluding that magnetic fields from power lines and household sources are a possible cause of cancer (18). This report, which was never made final, received a great deal of press coverage (42, 43) with controversy about both the content and the review process. That same year, after several years of development, the International Radiation Protection Association published international EMF exposure guidelines in a preliminary form (19). These guidelines, adopted in 1993, apply to both the public and workers, but were intended to protect against acute effects (e.g., nerve stimulation), with data on chronic effects (e.g., cancer) considered insufficient for setting guidelines. Additional evidence for possible health effects from EMF was published in 1991, including another study reporting an increase in childhood leukemia (20) and one reporting increased risk of male breast cancer with occupational EMF exposure (21). Despite this added evidence, a new expert panel, convened by the President s Office of Science and Technology in 1992, concluded in a report that there is no convincing evidence in the published literature to support the contention that exposures to extremely low frequency EMF generated by sources such as household appliances, video display terminals, and local power lines are demonstrable health hazards (27). This panel further suggested that research on EMF should not receive a high priority. Contrary to the panel s recommendation and based largely on the desire of both the general public and utilities to develop firm scientific conclusions, the US Congress passed the Energy Policy Act in 1992 (28), authorizing funding for the Research and Public Information Dissemination Program. The program, jointly funded by industry and government, was to provide scientific evidence to clarify the potential for health risks from EMF exposures (39) and was expected to yield research findings and a risk assessment within 5 years. An advisory group of the National Radiological Protection Board in the United Kingdom also published the first of its series of ongoing EMF reviews in 1992 (26). Its findings included no firm evidence, but pointed to some consistency with regard to childhood brain tumors. Evidence was judged only sufficient to justify formulating a hypothesis for testing by further investigation. The EMF issue was subject to intense media coverage in Over 70 news stories appeared in the US popular media that year, compared with 20 in 1992 and 25 in 1994 (Catherine Lynch, RS Banks EMF Information Project, personal communication, July 16, 1998). One source of news was a study linking the use of electric appliances to adult leukemia (31). Although the published findings were widely covered in the popular media, the results may have been due to bias (44, 45). With heightened media attention, policies on EMF were changing. The Swedish government advocated prudent avoidance, following the recommendation of the Swedish Electric Board, and the California Public Utilities Commission adopted a policy that included development of no- and low-cost field reduction measures for new electrical facilities and establishment of a research program. In 1996, the National Research Council of the National Academy of Sciences released its evaluation of EMF health effects from residential exposure (2). Its widely publicized conclusion was that there is no conclusive evidence that electromagnetic fields play a role in the development of cancer, reproductive and developmental abnormalities, or learning and behavioral problems, or that they are a threat to human health. The report noted, however, that an association between wire codes and childhood leukemia persists in

3 S52 Kheifets et al. TABLE 1. History of electric and magnetic fields at a glance Year(s) Selected positive scientific finding Public/policy response 1960s Mid 1970s Early Soviet occupational reports of symptoms in workers exposed to extra-high electric fields (7) Hearing on New York 765-kV line Research programs established (DOE*, NYPLP*, EPRI*) Wertheimer and Leeper study finds increased rates of cancer in children in high-wire-code homes (8) Milham study reports higher leukemia rates for electrical occupations (9) Study finds developmental effects in miniature swine exposed to electric fields (10) Results of NYPLP studies published (11), including study of Savitz et al. (12) finding a stronger association of childhood cancer with wire codes than with measured fields Henhouse study finds developmental abnormalties in chick embryos exposed to pulsed magnetic fields (17) London et al. childhood leukemia study supports Savitz et al. results (20) Matanoski et al. report increased breast cancer risk in occupationally exposed males (21) Swedish studies report increased risk of leukemia in exposed children and adults (23 25) Canada-France study reports an association between electric and magnetic fields and leukemia (29) Loomis et al. report links work in electrical occupations and female breast cancer (30) Lovely et al. study finds increase in adult leukemia with electric appliance use (31) University of North Carolina study indicates elevated risk of brain cancer in electric utility workers (32) NCI* study reports negative results for childhood leukemia (34) NTP* study finds no effect of electric and magnetic fields on cancer promotion in rats (35) NIEHS* report to congress at the conclusion of the RAPID Program (39) NCRP* report on potential health effects of electric and magnetic fields commissioned by EPA* Prudent avoidance suggested as a policy option in the OTA* report (13) Brodeur s New Yorker articles point to electric and magnetic fields as a cause of cancer (14 16) Florida sets magnetic field limits EPA draft report: magnetic fields a possible cause of cancer (18) IRPA* establishes guidelines on exposure to electric and magnetic fields (19) Gibbs review recommends prudent avoidance in Australia (22) NRPB* review: no firm evidence; further research justified (26) Oak Ridge report recommends no further research (27) Energy Policy Act (28) mandates RAPID* program to study health risks from electric and magnetic fields Colorado Public Utilities Commission adopts prudent avoidance Swedish government advocates prudent avoidance California adopts no-and low-cost field reduction measures CDHS* electric and magnetic fields research program is established Covalt decision: electric and magnetic fields are under jurisdiction of Public Utility Commission, not courts NAS* report: evidence inconclusive, but childhood leukemia-wire code association persists (2) German government adopts electric and magnetic field regulations (33) National Action Plan on Breast Cancer calls for more research on electric and magnetic fields (36) Revised ICNIRP* guidelines published (37) RAPID Working Group classifies electric and magnetic fields as a possible carcinogen (38) NIEHS proposes passive regulation (39) * Abbreviations: DOE, US Department of Energy; NYPLP, New York Power Line Project; EPRI, Electric Power Research Institute; NCRP, US National Council on Radiation Protection and Measurements; EPA, US Environmental Protection Agency; OTA, US Office of Technology Assessment; IRPA, International Radiation Protection Association; NRPB, UK National Radiation Prtection Board; RAPID, US Research and Public Information Dissemination Program; CDHS, California Department of Health Sciences; NAS, US National Academy of Sciences; NCI, US National Cancer Institute; NTP, US National Toxicology Program; ICNIRP, International Commission on Non-Ionizing Radiation Protection; NIEHS, National Institute of Environmental Health Sciences. multiple studies, although the causative factor has not been identified. As with past expert reviews, the National Research Council report seemed to only add fuel to the EMF controversy, as it came from a prestigious institution and reached a negative conclusion. Three members of the National Research Council panel, all past presidents of the Bioelectromagnetics Society, issued a press release (46) to balance out the press release issued by the National Research

4 EMF and Cancer S53 Council. That same year, the German federal government published the first national EMF regulation (33), based in part on the draft standards developed by the International Commission on Non-ionizing Radiation Protection (see below). The following year, investigators at the National Cancer Institute published the largest childhood leukemia study undertaken to date (34). Though the authors interpreted the results as completely negative, other epidemiologists did not. An accompanying editorial in the New England Journal of Medicine, however, declared the EMF issue resolved and called for no further research (47). Both the article and the editorial received wide coverage in the popular media. Separately, the National Action Plan on Breast Cancer organized a meeting at which a panel of scientists concluded that their research findings on EMF and breast cancer suggested an effect and that further research was required (36). Guidelines for occupational and public exposures to power and radio frequencies were revised and published in 1998 by the International Commission on Non-ionizing Radiation Protection (37). These guidelines, which established lower ceiling limits than previous ones, were again based on acute effects, such as stimulation of peripheral nerves and muscles. Research on long-term effects, such as cancer, was considered insufficient to provide results. Also in 1998, the National Institute of Environmental Health Sciences convened a Working Group to prepare its report to Congress at the conclusion of the Research and Public Information Dissemination Program. The Working Group, using carcinogen classification criteria established by the International Agency for Research on Cancer, categorized environmental magnetic fields as a possible carcinogen, based primarily on human data for childhood leukemia and for chronic lymphocytic leukemia in occupationally exposed adults (38). For other health outcomes, including other cancers, reproductive disorders, and neurodegenerative and cardiovascular diseases, it concluded that the evidence was inadequate to either support or rule out a causal relation to environmental EMF exposure. The conclusions of the National Institute of Environmental Health Sciences Working Group were broadly consistent with the earlier National Academy of Sciences/National Research Council report. The Working Group, however, moved slightly in the direction of accepting the possibility of a causal interpretation. This slight difference in the reports was exploited in the media: headlines for the National Academy of Sciences report read Panel Sees No Proof of Health Hazards From Power Lines (48), while National Institute of Environmental Health Sciences coverage stated Electric Fields Linked to Leukemia (49). At the end of 1998, the US Department of Energy, facing budget cuts, chose to eliminate the $6-million-a-year basic research program on EMF bioeffects. This action and the conclusion of the Research and Public Information Dissemination Program left only the Electric Power Research Institute as a funder of targeted EMF research in the United States. A number of studies already funded by the National Institutes of Health continued. In 1999, the National Institute of Environmental Health Sciences released its report to Congress (39). While the report did not formally classify extremely low frequency EMF as a possible carcinogen, it concluded that extremely low frequency EMF exposure cannot be recognized as entirely safe because of weak scientific evidence that exposure may pose a leukemia hazard. ISSUES AROUND EPIDEMIOLOGY AND POLICY Risk perception and public concern The public concern about EMF and cancer that developed during the 1980s can be attributed in part to risk perception. EMF health risks have several characteristics known by researchers in the field of risk perception to increase perceived risk (50): 1) there is a highly dreaded outcome (cancer) that, moreover, affects children; 2) the risk is poorly understood by scientists and unfamiliar to the public; and 3) the risk may be viewed as inequitably distributed and involuntarily imposed. The EMF case points to a general need for epidemiologists to familiarize themselves with the psychology of risk perception, to consider potential public concern in their work, and to attempt to put risks and research results in perspective for the public and the media. Public concern is a consideration in setting epidemiologic research agendas on environmental and like issues with direct public implications. Public concern can create political pressure and even mandates for research on specific issues. This research may be carried out by governmental organizations; for example, Congress mandated that the National Cancer Institute carry out a study of cell phones and brain cancer (51). Alternatively, researchers may respond to funding opportunities. Ideally, decisions about research funding should be driven by both the quality of the science and the relevance and importance of the research to public health. But when research is paid for with public funds, the influence of other factors, such as public perception, is sometimes apparent. Some research will investigate possible risks of which the public is not yet aware and thus will not be influenced by public concern. Other research will involve study of risks about which the public is aware but not greatly concerned. This research may nonetheless be important from a public health perspective, and lack of public concern should not be a deterrent to pursuing it. Research may sometimes provide evidence that leads to public controversy, as has been the case with EMF. Controversy is not created by research findings alone, since information is most often filtered through the news media before reaching the public. Various theories have been developed about how the media influence public perception of risk (52). As already noted, the EMF controversy has several characteristics that enhance public concern. Epidemiologic research, particularly if it is related to the environment, is likely to address topics perceived by the public as involving risk and controversy. The EMF issue provides examples of three sources of controversy that may surround epidemiologic research. First, controversy arises when conflicting or incomplete research results call into question the existence of a public health problem (27, 39).

5 S54 Kheifets et al. Second, there may be controversy over what should be done about a possible risk, because of differing views on the exposure responsible for the risk, the control measures to reduce it, and the costs, benefits, and ethical considerations involved (53). Third, controversy may reflect uncertainty as to who is responsible for a risk and for managing it (53). Controversy about risks may be resolved by additional research, although not always, and consensus among scientists may not be adequately presented to, or accepted by, the public. Public understanding may be improved with clearer communication of findings and review and synthesis of research results by expert groups. In the case of EMF, reports by review groups on EMF risk over the last few years helped to improve public access to results; however, they offered seemingly different conclusions based on complex results. Differences in scientific interpretation are often further exacerbated by media coverage that tends to present extremes of opinions, often from individual experts, without providing any clear basis for assessing their validity. The findings of scientific review panels, and even the bases for considering them, may be called into question. However, expert panels are critical for synthesizing scientific evidence, and convergence in the findings of multiple panels can be useful. Cost-benefit analysis and research funding The question of whether EMF research should continue or stop has been raised repeatedly (47). As experience to date has shown, the likelihood of a research breakthrough in a given period of time is important. Other considerations include research costs, the availability of funding, and the relative value of other research competing for funds. The societal cost of continuing uncertainty is difficult to estimate but must also be considered. Scientists views on further research may also be influenced by their values and research capabilities; career concerns may come into play as well. Scientists committed to a particular area (e.g., ionizing radiation) might be more skeptical of new areas; others (e.g., EMF researchers) may not move readily to other areas of research. Decisions on funding policy-relevant research, however, are driven by diverse considerations extending well beyond the scientific community alone. As in the example of EMF, the prevalence of exposure and societal importance of the diseases or health outcomes under investigation receive weight, as does the potential public health impact of exposure. The degree of public controversy or concern is another consideration since public concern or continued uncertainty (or both) can lead to real costs that may justify continuing research. Funding decisions may also have a basis in the costs and benefits of mitigation measures, as well as in benefits that might arise from societal consensus that a hazard does not exist. Not funding research might leave a hazard undetected, with a missed opportunity to improve public health. Funding for one topic can reduce resources for addressing others, but this trade-off is not always straightforward, especially for controversial topics. As illustrated by the EMF case study, combined consideration of patterns of apparent risk and exposure observed in epidemiologic studies may have significant policy implications. A risk may be large but caused by unusual exposure conditions affecting only a few people. Alternatively, a risk might be small for any one individual, but public health impact could be substantial due to a prevalent exposure. Excess morbidity and mortality might be comparable in the two cases, however, appropriate policy responses might be quite different. If, for example, the per-exposed-person cost of eliminating the risk is similar in both cases, a small pervasive risk may be accepted because the cost of control may not be justified by the achievable total reduction in morbidity and mortality. In contrast, the total cost of eliminating a large individual risk due to rare exposure circumstances may be much lower, as exposure reduction would be needed for a relatively small number of people. Public health priorities for control measures are typically set with regard to the population attributable risk in order to do the most good for the most people. Using this rationale, recommendations have been made that EMF research concerned primarily with rare diseases, like childhood leukemia and male breast cancer, should not continue. Even for diseases as rare as childhood leukemia, however, the small risks detected using epidemiologic methods, associated with a prevalent exposure, potentially convey substantial population attributable risks and theoretical lifetime risks that exceed those for many agents now regulated on the basis of animal bioassay data (38). This lesson has been repeatedly forgotten in the EMF debate, in which difficult to study has often been confused with unimportant to society. Equity in the distribution of risks is receiving increasing consideration. High individual risks, even if rare, will motivate research and mitigation. Although not yet a key element of discussion, the degree to which racial, ethnic, and socioeconomic groups are differentially subjected to greater risk may become part of the EMF risk issue, as it has for other environmental agents such as air pollution (54). LESSONS LEARNED A number of issues specifically relevant to EMF provide insight into the relation between research and policy. Among them are needs for interdisciplinary collaboration and for an interface with risk assessment whenever epidemiologic research is used in policy-making. Interdisciplinary collaboration and communication EMF research requires the transdisciplinary expertise of epidemiologists, statisticians, exposure assessors, toxicologists, molecular biologists, cell biologists, physiologists, endocrinologists, biophysicists, and physicists. Achieving sufficient interdisciplinary dialogue has been difficult, in part because of the diverse disciplines involved and the highly technical nature of some aspects of research. Conceptual approaches to research and semantic differences across disciplines are partially responsible. Another problem is that grant-based funding programs, as well as career incentives, encourage discipline-specific research that has produced a scattering of largely unrelated findings regarding

6 EMF and Cancer S55 EMF. The tendency of many scientists to accept their own results and those of their own field more readily than those of other fields is also a factor. Lastly, different disciplines have different methods for developing research strategies and interpreting results. Physics, toxicology, and epidemiology, for example, differ in both theoretical and interpretative approaches; epidemiologists largely use observation while physicists and toxicologists base their work in models or in experiments. As a result, scientists from experiment-oriented disciplines may be dismissive of epidemiologic data as soft and subject to biases. The approaches used by epidemiologists to handle bias and its consequences may not be considered sufficiently rigorous by scientists from other disciplines who can control the circumstances of their experiments. In an animal bioassay, toxicologists, for example, set the exposure protocol, select the species and the number of animals for investigation, and can make noninvasive and invasive measurements at will. They can study multiple species and both sexes. Epidemiologists, in contrast, are left with the circumstances of natural exposures and study populations of a size and nature driven by accessibility and feasibility, given resource restraints. Bias is controlled for by design and in analysis. The potential for bias in epidemiologic studies is widely accepted and enters into the interpretation of epidemiologic data. Despite the experimental setup, bias and effect modification might be present in toxicologic studies as well, but are rarely examined or discussed. Neither the toxicologist nor the epidemiologist may be able to achieve an adequate sample size, or the state of the evidence may not provide a clear indication of the anticipated effect for sample-size estimates, regardless of research approach. Although the theory-driven research of physicists contrasts with the intermittently deductive and inductive approaches of epidemiologists, physicists have been involved in research on EMF, including epidemiologic research. They have worked on developing measurement equipment and exposure classification strategies, and have also been deeply involved in considerations about potential mechanisms of cellular injury. Approaches to assessing the quality of research data also differ across disciplines. These differences may lead to prejudice on the part of experimentalists against observational data. As an example, toxicologic work often comes under protocols for Good Laboratory Practice, while standards for observational epidemiologic studies have not been implemented, leaving investigators to establish their own procedures. Typically, epidemiologic studies are not subject to auditing. Epidemiologists could learn from practices in other disciplines by adopting more rigorous methods for quality assurance and control in data collection and management. Exposure assessment and statistical approaches EMF research typifies the challenges that epidemiology needs to meet in order to inform risk assessment and policymaking. For making policy and setting standards, an understanding of the nature of the exposure-response relation is crucial. This area of analysis is always challenging for epidemiologists, who may be limited in their approach by the extent of available data. Ideally, modeling of the exposureresponse relation would be based in a biologic framework, but for EMF this framework has been lacking. A variety of EMF exposure measures have been used in epidemiologic studies, but which is the most biologically appropriate is uncertain. The studies have generally included an estimate or surrogate for average exposure. Cumulative exposure has also been estimated. While most recent studies of residential EMF and childhood cancers have used spot and 24-hour exposure measurements, wire codes have also been used as a surrogate to estimate exposure. Some studies using wire codes have directly measured magnetic fields as well, but have not reported average field strengths for wire-code categories. Scoring wire-code categories by average magnetic field strength and calculating quantitative and continuous exposure estimates would have improved these studies. In general, the studies have not taken an integrated approach to exposure assessment. Methods that combine residential and occupational EMF exposures as well as exposures from different sources (e.g., appliances with wire codes or measured fields) into average or cumulative field strength estimates would improve exposure estimates. The choice of exposure categories and the specification of an analytic model should be based in biologic understanding. Absent a firm basis, exposure stratification is usually based in the distribution and linear models, typically without threshold, assumed for exposure-response analysis. Depending on the findings, these choices may ultimately have policy implications, as categories without significant risk may be misinterpreted as safe, or a linear nothreshold exposure-response relation may be considered without sufficient exploration of the alternatives. The needs of policy-making may too simplistically be considered met if an exposure cutpoint or a binary exposure scale can be identified that might be the basis for determining a standard. The risk of disease on either side of a cutpoint, however, is a complex function of the shape of the underlying exposure-response curve in that exposure range and of the distribution of exposure within that range in the study population. Differences in exposure distributions can produce contrasting pictures of disease risk that may not be generalizable from one study population to another, even if they both share an identical exposure-response function. In creating exposure categories, investigators sometimes try to take policy considerations into account by structuring the lowest category to include a large portion of the study population or to correspond to some existing cutpoint. The reasoning, in addition to statistical considerations, is a prior assumption that reductions in exposure within the low range will not be feasible and that only risks at the higher exposures will be of policy interest. Variation in exposure distribution or in the exposure-response curve in a large baseline or reference exposure category, however, can alter the apparent strength of the association under study. While the slope estimate, or estimated change in response, for a unit change in exposure is easily obtained, it

7 S56 Kheifets et al. is not regularly reported either in epidemiologic studies in general or in EMF studies in particular. Both the slope estimate and its confidence interval are useful in risk assessment. With a slope estimate, preferably supplemented by a flexible analysis of trend, risk assessors can estimate the increase in risk that would be expected to occur from any specified increase in exposure levels. This risk estimate, however, should not be extrapolated to exposure values outside the range examined in the studies. Communication Communication of findings plays an indispensable role in the translation of epidemiologic research into public policy. Communication and discussion at every stage of research could increase the contribution of epidemiology to policymaking. Currently, discussion with stakeholders is limited until results have been published. Input from risk assessors, decision-makers, and policy analysts as studies are developed and data are analyzed and reported could enhance the utility of evidence for policy-making. Interaction with risk assessors, for example, included on advisory panels for studies could shape analyses to be as useful as possible for risk-assessment purposes. There are barriers to open research communication. Scientific journal policies that discourage disclosure of results prior to publication, as well as intense popular media coverage of the EMF issue, have led investigators to guard their findings. Epidemiologists have thus become less open to sharing preliminary results with colleagues and to presenting them at scientific meetings. Less pre-publication peer review of results and interpretations can decrease the scientific quality of research and reduce its use in risk assessment and policy-making. For hot topics like EMF, post-publication peer review may also be demanding of epidemiologists. While postpublication peer review can identify problems or research needs, limited time and funding make many epidemiologists reluctant to take part in this process. Additionally, industry or other well-funded interest groups may be able to support intensive post-publication evaluations, which researchers may find burdensome and distracting from their research focus. Including support in research proposal budgets for translational activities, such as post-publication peer review, risk assessment, and policy evaluation, could be a solution. Epidemiologists may also face the challenge of maintaining objectivity about their published data as it is evaluated postpublication by others and used in policy contexts. They may also seek to enhance future funding prospects by maintaining a high public profile. Post-publication peer review and risk assessment, as translational steps, speak to the relevance of epidemiologic study, which typically is less than perceived at the time of publication. Epidemiologists could help educate the press, the public, and policy-makers by making it clear that the study of the week is seldom as definitive as it may seem. So that published results will be recognized as more tentative and preliminary than final, Poole (55) has suggested considering a publication as work that is closer to the beginning than to the end of the peer review process. Integrating research into the existing literature through comparative meta-analysis is another way of assessing its contribution (56, 57). Since individual study reports usually cannot fully integrate the new results with previous findings, metaanalysis may require a separate report, or simply a willingness to provide results for meta-analysis or pooled analysis by others (58 60). The inclusion of policy recommendations in reports of epidemiologic research has been the subject of much discussion. The types of policy statements made in the discussion sections of research papers are usually too general to be of much practical utility, since not all of the options and facts required to determine the implications of the research for policy alternatives are available. For example, the analysis of such questions as whether power lines should be moved or reconfigured or whether appliances should be redesigned, labeled, or banned would exceed the bounds of research findings. Another consideration is the conflict between public health advocacy and dispassionate scientific research and reporting. Epidemiologists need to remain free to advocate when appropriate; however, the stronger the advocacy stance taken, the greater the conflict of interest for those continuing to conduct additional research on the same topic. It is questionable whether the advocate can objectively collect and analyze subsequent data and be perceived as objective after taking a visible stand on a charged issue such as EMF, as its history has shown. In communicating results for risk assessment and policymaking, a clear distinction should be made between evidence of the absence of an effect and the absence of evidence of an effect. Epidemiologists often state that studies failed to detect an association when they mean that the possibility of no association could not be precluded. Negative studies are informative if they provide some evidence against effects of sizable magnitude and in favor of little or no effect. An additional difficulty is that a risk at the limit of detection in epidemiology may still be large from a public health or policy perspective. An appreciation of the gap between epidemiologic detectability and significance in the policy arena is essential in the interpretation of epidemiologic studies in the context of risk assessment, policymaking, and risk communication. CONCLUSION The degree to which the public is concerned about an epidemiologic issue depends upon its perception of the associated risks. Perception of health risks can be strongly influenced by media reporting of research results, as has been the case with EMF, and by the nature of both risks and associated exposures. Personal and societal costs and benefits of avoiding or accepting risks also affect risk perception and public concern. Public concern influences researchers, public health professionals, and funding agencies setting epidemiologic research agendas both directly and through its impact on policy. Epidemiologic research itself can lead to scientific and public controversy. Controversy arises from inconsistent research results and methodological problems. Also involved are diffi-

8 EMF and Cancer S57 culties in the interdisciplinary communication and collaboration required for EMF and other epidemiologic research. Reluctance to accept results from other fields due to methodological differences may contribute to controversy, especially if disagreements become the subject of media attention. An additional problem is the lack of consensus among epidemiologists and other scientists regarding the policy implications of reporting uncertain results. Some advocate presenting evidence as either clear and convincing or not; others prefer to indicate their degree of confidence and the potential magnitude of effects despite the possibility of public overreaction. More effective communication, as well as a deeper understanding of risk perception, on the part of epidemiologists could help to put risks in perspective for the public and the media. Review by expert panels might improve public understanding of research results. Discussion among researchers, risk assessors, and policy makers throughout research programs could both increase their contribution to policy-making and improve study design and analysis of results. Post-publication peer review and risk assessment can help impart perspective on the importance of research studies to policy makers and the public. It is clear that, whatever the outcome with regard to health effects, pursuit of the EMF issue has brought a number of methodological and policy concerns into sharper focus. ACKNOWLEDGMENTS The authors gratefully acknowledge Sonia Singh and Ajay K. Sethi for their assistance during the work group meeting and in the development of the draft manuscript. The authors would also like to thank Dr. Jonathan Samet and Nora Lee for their editorial suggestions. DISCLOSURES Dr. Leeka Kheifets holds the position of Head, Radiation Studies Program at the World Health Organization. Previously she was a Technical Executive at the Electric Power Research Institute, where she directed the EMF research program. She is also on the faculty at Stanford University School of Medicine in the Department of Health Research and Policy. She has served on National Academy of Sciences, Institute of Electrical and Electronics Engineers, and National Council on Radiation Protection and Measurements committees. Dr. Kheifets was also a member of National Institute of Environmental Health Sciences and International Agency for Research on Cancer Working Groups charged with evaluating potential health effects from EMF exposure. Dr. Ray Greenberg was appointed as President of the Medical University of South Carolina in For 5 years previously he served as Vice President for Academic Affairs at the Medical University, and before that he was the founding dean of the Rollins School of Public Health at Emory University. A former president of the American College of Epidemiology, Dr. Greenberg also served as the chair of the Epidemiology and Disease Control Study Section for the National Institutes of Health. He served on an external advisory board to the National Cancer Institute on a study of EMF and the risk of childhood cancer. He also chaired a panel for the Harvard Center for Risk Analysis on this topic. Dr. Raymond Neutra is Chief of the Division of Environmental and Occupational Disease Control in the California Department of Health Services. This Division provides technical support to state and local agencies and carries out research and investigations. He has also been Chief of the 8-year Electric and Magnetic Field Program for the department. This program was mandated by the California Public Utilities Commission, and by the order of the Commission was funded by California Utilities. It was advised by stakeholder consultants, including concerned citizens, utilities, the electrical workers union, and public interest groups. The program funded extramural research on EMF exposure, epidemiology, risk evaluation guidelines, risk evaluation, and policy analysis. Dr. Gordon Hester holds the position of Manager, Energy Analysis in the Environment Division of the Electric Power Research Institute. In that position, he has directed studies on risk communication regarding exposures to EMF and studies of alternatives for reducing EMF exposures. He was previously a graduate student and postdoctoral researcher at Carnegie Mellon University, where he also conducted studies of EMF risk communication. Dr. Charles Poole conducted a study of depressive symptoms and residential proximity to electric power transmission lines, which he published in He has authored or coauthored numerous review articles, commentaries, editorials, and meta-analyses pertaining to the epidemiology of EMF. Dr. Poole has served on expert panels pertaining to EMF for the North Atlantic Treaty Organization, the United States Environmental Protection Agency, the National Institute of Environmental Health Sciences, the Institute of Electrical and Electronics Engineers, and the Electric Power Research Institute. He has provided consultation services on EMF epidemiology to a wide range of governmental agencies, public utilities, corporations, law firms, trade associations, and other organizations. Ms Gail Lundell is a science writer and editor for the Electric and Magnetic Fields Health Assessment Program at the Electric Power Research Institute. She has coauthored, written, or edited numerous publications on the potential health effects of exposure to EMF. She has also worked on documents in the areas of risk evaluation, exposure assessment, and environmental policy, as related to EMF. 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