Public health journals regularly include articles that take swipes at the methods, the direction, the role, and the purpose of epidemiology. Many of the articles, often written by epidemiologists and other public health practitioners, have provocative titles such as "Questioning Epidemiology: Objectivity, Advocacy, and Socially Responsible Science" or "Epidemiology and the Web of Causation: Has Anyone Seen the Spider?"
"These debates have been going on for decades," said Jonathan Samet, M.D., chairman of epidemiology at the Johns Hopkins School of Public Health, Baltimore. "Certainly, these questions are fundamental to all scientific disciplines. Epidemiology is not unique."
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The article, by medical historian and philosopher Mark Parascandola, Ph.D., a fellow in the Department of Clinical Bioethics at the National Institutes of Health, uses the tobacco industry's long-standing criticism of epidemiologic links between smoking and lung cancer ("mere statistics") to trace the historical roots of epidemiology. The tobacco industry and other critics of epidemiology have successfully fostered a "strategy of denial," he said, by taking advantage of widespread skepticism about the science of epidemiology.
"It is not only epidemiology's critics who view its conclusions as second rate," Parascandola wrote. "Epidemiologists themselves are unduly self-conscious and skeptical about their own methods."
Central to the discussion is a comparison of the inductive reasoning methods of epidemiology and the deductive processes of laboratory science. The article depicts critics of epidemiology as staunchly believing that the experimental environment of laboratory science eliminates uncertainty, while epidemiology provides only "circumstantial" evidence derived from observations.
"Causal Inference"
In an interview, Parascandola said the article evolved from philosophers' historical interest in "causal inference."
"How do you get from a number of observations to the inference that there is some general cause or laws of nature that begin those observations?" Parascandola asked. "I think epidemiology is a particularly interesting place to look at that philosophical question, because that's what they do. They make causal inferences, often from limited data."
Epidemiologists acknowledge, even welcome, the debate that periodically swirls around their profession, but they are quick to reject any suggestion that their science is second rate.
"Debate is very healthy in any discipline, and introspection is extremely important," said Margaret Spitz, Ph.D., head of epidemiology at the University of Texas M. D. Anderson Cancer Center in Houston.
Weak Science?
"There has been a tremendous amount of debate about epidemiology, especially in the epidemiologic press, but the issue is not whether epidemiology is a weak science," Spitz said. "I don't think that's even worthy of discussion, because there is no doubt in my mind that epidemiology has contributed enormously to the identification of risk factors for the leading causes of mortality and morbidity in the last half century."
Harvard's Walter Willett, Dr.P.H., M.D., said epidemiologists have "too much work to do to spend a major bit of our time defending our field."
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National Cancer Institute epidemiologist Aaron Blair, Ph.D., said that "many people, maybe even some scientists, have the expectation that science is definitive, that there's never any debate about science."
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In fact, he said, "we keep changing paradigms as we gather more information. What science does is give you a method for progress."
Competing Interests
Philosophical debates over epidemiologic findings reflect both the scientific process and competing societal interests. "If you're studying environmental exposure, for example, one study may suggest that some new environmental exposure causes cancer," said Blair. "There will be a very clear and careful evaluation of that data and presentation of another interpretation from one segment of society, typically from the industrial side.
"On the other hand, if you're studying a chemical that many people already think poses a problem, but a study suggests that it isn't much of a problem, you will again have a thoughtful review . . . and presentation of the other side's view."
"We operate in a democratic society, so all studies are looked at very carefully and critically. That's what allows progress to occur. At the same time, what the public hears is disagreement. In many issues involving epidemiology, disagreements become extremely public, appearing on the front page of newspapers and on radio and TV. That rarely happens with physics."
Criticism of epidemiology does not reflect a flawed scientific discipline but rather the prominence of findings that emerge from epidemiologic investigations, said Samet.
"Examples [of the prominence] are abundant, but an easy one is the tobacco industry," said Samet. "For about 50 years the industry has been attacking the credibility of epidemiologic research because that research has told the world that tobacco is killing people."
"A far more subtle example would be the serious questions that have arisen about using epidemiologic findings as a basis for air quality regulations. Two years ago we promulgated a standard for fine particulate matter in this country, a standard that has substantial implications for industry. Epidemiologic findings were largely the basis for the new standard, and what we've seen are attacks on the credibility of the science."
The debate and criticism also reflect the difference between the type of scientific evidence needed to prove a cause-and-effect relationship versus the evidence required to effect public policy.
"The relationship between smoking and health is a classic example," said Parascandola.
"We have this evidence. Should we tell people to stop smoking or not?" he asked. "It becomes an issue of how much evidence we need to have before we can say that smoking is the cause of lung cancer."
Blair pointed out that the so-called definitive laboratory indictment of smoking as a cause of lung cancer came long after epidemiology had proven the case to the satisfaction of most people.
"When studies showed that tars and other components of cigarettes caused mutation of the p53 gene, it made front-page headlines and all the TV news shows, which hailed it as the definitive proof," said Blair. "In fact, the definitive proof had come from epidemiology two decades before. The data were just overwhelming."
"The idea that you had to have [proof] in some sort of glassware before you could say that [smoking causes cancer] just doesn't make any sense to me," Blair added. "We have lots of examples of things that happen in the laboratory but appear not to happen in living systems. The real test, obviously, is what happens to us, to humans."
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