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In searching for rules to live by, the choices are sometimes hard. To put these two axioms in different terms, we all want to avoid risks, but few of us are willing to allow our lives to be dominated by fear. Or, as David Ropeik of the Harvard Center for Risk Analysis puts it, "We have to recognize that there are very real risks out there, but one of them is fear." i
Some fear is a good thing when the risk is certain. But it can be counterproductive, even dangerous, to overreact, or to be scared for no good reason. And there's the rub. What is a "good reason" for being scared? There is only one way to figure that one out.
Look at the evidence. 
American regulatory agencies historically make their decisions about the safety of products on the weight of the evidence. Not on proof, for it is impossible to prove that something is absolutely safe. Putting it in terms of human health, if we know a certain chemical makes laboratory rats sick at a certain dose, if the mechanisms causing the sickness are relevant to humans, and if some humans are exposed to roughly the same dose that causes sickness in laboratory rats, we assume that humans would get sick as well. We don't need to wait for proof that it makes people get sick. The government takes action and restricts, or bans, the use of the chemical. You might say that the government acts in a precautionary manner. In fact, it routinely multiplies its precautionary bet. It converts the danger point for laboratory rats into human terms - and then builds in a safety factor, for example, of 100 or 1,000 to establish a safety level well below the possible risk point.
Some people sincerely believe that if a chemical causes harm to lab animals at any level, humans shouldn't be exposed at all. But as one student of risk, Aaron Wildavsky, put it, sincerity is not a replacement for science. ii Regulations are going to be based either on public opinion (and sometimes are in some countries) or on evidence. Or, as Wildavsky put it, "preferences, yes; disregard of science, no." iii In any event all chemicals cause harm to laboratory rats at some levels, and avoidance of all chemicals at any exposure levels is simply not possible. Almost all substances, even water, can be expected to cause harm.
Language relating to the accepted application of precaution was adopted in the 1992 Rio Declaration on Environment and Development and reaffirmed in the 2002 Report of the World Summit on Sustainable Development (WSSD):
"In order to protect the environment, the precautionary approach shall be widely applied by States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation."
The key phrase in the definition adopted by the world's governments in 1992 and reaffirmed in 2002 is "cost-effective measures." By the time of the 2002 Summit, governments were becoming increasingly concerned about the negative aspects of being overly cautious in regulation. Thus, in the 2002 Report, countries promoted a science-based approach to decision-making and downplayed the value of precautionary measures.
However, some advocacy groups ignore the views of world governments and promote a restricted version of precaution, crafting a more ominous variation: "When an activity raises threats of harm to the environment or human health, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically." The words "serious" and "irreversible" are gone, which presumably is meant to lower the threshold for government action. But the underlying principle survives - there has to be a threat of harm. But how can a threat of harm be established? There is only one way, and that is to weigh the evidence, not to base a decision on the depth of emotion, or the heat of the debate. Writes Wildavsky: "A responsible person cannot just believe but must have reasons derived from evidence." iv
i The New York Times, December 2, 2002, p. F2
ii Wildavsky, Aaron, But Is It True? A Citizen's Guide to Environmental Health and Safety Issues (Cambridge, Mass.: Harvard University Press, 1997), p. 10
iii Ibid. p. 9
iv Ibid, p. 428
Last Updated: July 16, 2003
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