Best Available Science vs Uncertainty

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Published on Friday, 12 September 2008 08:00
Source: The Peter Sandman Risk Communication Website Science is indeed the pursuit of “universal facts and principles.” But scientific findings are always a rough draft of those universal facts and principles, subject to amendment as new data identifies errors or exceptions, different facts or better principles. Non-scientists tend to miss this important truth, seeing science as definitive rather than tentative. That’s partly our hunger for certainty at work. But it’s mostly the fault of scientists, who make two fundamental risk communication mistakes again and again: Scientists try to augment the authority and prestige of the scientific enterprise by implying that science builds on a firm foundation of prior science. They know better. In fact, science builds on parts of the foundation; it keeps tearing down other parts to rebuild them better. Scientists try to augment the authority and prestige of particular scientific claims by implying that those claims are firm. Once again, they know better. When they write for their peers, they are at pains to address the competing claims of other scientists. But when talking to the public, they all too often ignore those claims or disparage them as not scientific at all. The more controversial the claim, unfortunately, the likelier a scientist is to commit this sin on behalf of his or her side of the controversy. Falsifiability is the fundamental premise of all science. If there is no possibility that you could be proved wrong by new data, you’re in the realm of faith, not science. If there is such a possibility, your findings are tentative by definition. (This is an oversimplification of Karl Popper’s notion of falsifiability, but I think it captures the essence of his point.) Of course some scientific claims have stood firm for centuries, and are likely to stand firm forevermore. Likely – but not guaranteed. Scientific claims that stood firm for centuries occasionally crumble; consider what Einstein did to Newtonian physics. Many scientific claims have never stood firm. Rather, they are endlessly under attack. Even claims that a majority of scientists consider well-established frequently coexist with a competing viewpoint advanced by a scientific minority. If 90% of the evidence supports one position and only 10% supports the other, most scientists are likely to go with the 90% – and a smart layperson should too. But in science as in horse-racing, sometimes the long shot comes from behind and wins. And depending on the cost of erring in each direction, sometimes it makes sense to hedge your bets – for example, to take precautions against a horrific risk even though most (but not all) experts believe it can’t happen. As a practical matter, moreover, new science is extremely tentative. Different scientists often advance competing and mutually incompatible claims simultaneously, all of them grounded in data. Further science must determine which of these claims are valid and which are false, or must find a new interpretation that integrates them and shows that they’re not mutually incompatible after all. Sometimes that further science turns up in a matter of weeks or months. Other times that further science relies on methodological or conceptual breakthroughs that haven’t yet occurred; we can (and often do) wait for decades without a good basis for choosing among competing scientific claims. Even if there are no competing claims, a new scientific claim has “stood firm” for minutes, not for centuries. At the very moment it is published a half-dozen other scientists may be hard at work on relevant studies that can confirm or disconfirm the new study – or, most likely, complicate its interpretation without quite confirming or disconfirming it. Wise scientists therefore take a new finding with more than a grain of salt, waiting to see whether additional studies will emerge that support or rebut it. Wise laypeople should do the same. And good risk communicators should help them do so – which is why communicating about uncertainty is so important. (See my 2004 column on “Acknowledging Uncertainty.”) The uncertainty of scientific findings and the inevitability of scientific controversies don’t have to lead to paralysis. In fact, once you understand that all science is uncertain, it becomes clear that uncertainty isn’t an acceptable reason (or excuse) for inaction. In coping with scientific uncertainty, the layperson has a fourfold job: Figure out what the weight of the evidence says. Or if that’s too difficult, figure out what the majority of the experts think – bearing in mind that their judgments may be biased or simply mistaken. Figure out how much residual uncertainty there is. Science is always uncertain – but there’s a real difference between the theoretical uncertainty of “all claims are falsifiable” and the practical uncertainty of “this claim is brand new and hotly debated.” Figure out what the cost of being wrong in each direction is likely to be. Often (but not always) over-caution about a risk does less damage than recklessness. When the disparities in outcome are big and the choice is uncertain, it’s not stupid to choose the option that won’t kill you if you’re wrong. Figure out whether you can afford to wait for new evidence that may reduce (or increase) the uncertainty. If new evidence is expected soon and the situation isn’t urgent, fine, wait. But when the time comes to act, take your best shot despite the uncertainty. And then keep looking for new evidence; you may want to change your mind or reverse your course. The risk communicator’s job is to help with these four tasks – or at least not to make them more difficult by implying that science is certain or that action should wait for certainty. As if all this weren’t difficult enough, I need to add one final factor. People’s decisions are rightly and inevitably grounded in more than just scientific evidence. Values play a role. So does outrage. So do a variety of other aspects of the situation. (See my January 2008 column on “Who’s Irrational: When People ‘Ignore’ Risk Data.”) Risk communicators not only have to help people cope with scientific uncertainty. We have to help them integrate what they know about the science with the rest of what they know, think, and feel.