Dangers to life and health abound. Even among the subset known to medicine and science, however, there is no guarantee that any particular danger will rise to the level of a recognized public health problem or elicit a response from the makers of public policy. The path from knowledge to policy is not straightforward; scientific consensus does not lead automatically to policy consensus. Judgments of what dangers should be most feared, how to explain them, what to do about them, and even whether they are public health problems at all are the outcome of social processes.1 A couple of examples may help to clarify these points.
In 1865—nearly twenty years in advance of Robert Koch's better-known discoveries—Jean-Antoine Villemin reported to the French Academy of Medicine that tuberculosis was a specific disease, transmissible by inoculation between animals and from man to animals.2 Villemin was a highly respected scientist, elected to the Academy in recognition of his work, his credentials impeccable. Nevertheless, his conclusions that tuberculosis was a contagious disease and that appropriate precautions should be taken were rejected not once but repeatedly by the Academy of Medicine.3 His conclusions were rejected not because his colleagues doubted his science but because they found the implications of his conclusions—for their own actions, for their patients, and for the relation between doctor and patient—socially and morally unacceptable. If tuberculosis was contagious, then its victims were dangerous to their family and [End Page 71] friends and, one physician said in a speech to the Academy of Medicine, "'What a calamity such a result would be! . . . [P]oor consumptives sequestered like lepers; the tenderness of [their] families at war with fear and selfishness.' The possibility was too horrible for him to contemplate. 'If consumption is contagious, we must say so in whispers' (Si la phthisie est contagieuse, il faut le dire tout bas)."4 Mandatory notification of tuberculosis cases to public health authorities did not become law in France until 1963, nearly one hundred years after Villemin had published his results.5
I owe my second example to the work of Karen Litfin on contemporary international efforts to regulate risks to the global environment.6 She contrasts the relatively successful action to limit destruction of the ozone layer embodied in the Montreal Protocol signed in 1987 by twenty-four countries (on which her monograph primarily focuses) with the inaction of governments in response to the threat of global climate change ("greenhouse gases"). There is broad scientific consensus that climate change is a "very, very real problem" and that the "social and environmental damage from global climate change is likely to be far more catastrophic than that caused by ozone depletion."7 There is, nevertheless, substantial scientific uncertainty as to the degree and timing of climate change; the costs of regulation are (as in my first example) perceived by policy and political actors as extremely high; the benefits (as well as costs) of action are unevenly distributed among rich and poor countries; and—perhaps most important—the risks of inaction are, at least in the short term, largely invisible. Immediate and credible threats (real or manufactured) are more often than not a sine qua non for public health action.8 The effects of climate change have not so far offered opportunities for the portrayal of risks comparable to the rhetorically and visually dramatic Arctic "ozone hole." And so, despite a strong scientific consensus in favor of regulatory action, opponents of action have so far prevailed.9
Policymakers require authoritative advice. Authority in public health is presumed to reside with experts in medicine and public health. Nevertheless, as the forgoing examples demonstrate, the credibility of experts and their power relative to other actors in the dramas of public health are limited, subject to a variety of contingencies. In this article, I identify and examine those contingencies in some detail, based on comparative cross-national research on policymaking in public health. I conclude that expert credibility and the authority of knowledge are contingent on the characteristics of political regimes; on the social and political location as well as the framing expertise of "knowledge brokers"; and...