While on the subject of public health policy making under conditions of ignorance, linguist Louise Cummings has recently published an interesting article about the logical fallacies used in the UK debate about possible human variants of mad-cow disease just over a decade ago (Cummings 2009).   Two fallacies were common in the scientific and public debates of the time (italics in orginal):
An Argument from Ignorance:

FROM: There is no evidence that BSE in cattle causes CJD in humans.
CONCLUDE:  BSE in cattle does not cause CJD in humans.

An Argument from Analogy:

FROM:  BSE is similar to scrapie in certain respects.
AND: Scrapie has not transmitted to humans.
CONCLUDE:   BSE will not transmit to humans.

Cummings argues that such arguments were justified for science policy, since the two presumptive conclusions adopted acted to guide the direction and prioritisation of subsequent scientific research efforts.  These presumptive conclusions did so despite both being defeasible, and despite, in fact, both being subsequently defeated by the scientific research they invoked.   This is a very interesting viewpoint, with much to commend it as a way to construe (and to reconstrue) the dynamics of scientific epistemology using argumentation.  It would be nice to combine such an approach with Marcello Pera’s 3-person model of scientific progress (Pera 1994), the persons being:  the Investigator, the Scientific Community, and Nature.
Some might be tempted to also believe that these arguments were justified in public health policy terms – for example,  in calming a nervous public over fears regarding possible BSE in humans.   However, because British public policy makers did in fact do just this and because the presumptive conclusions were subsequently defeated (ie, shown to be false), the long-term effect has been to make the great British public extremely suspicious of any similar official pronouncements.   The rise in parents refusing the triple MMR vaccine for their children is a direct consequence of the false assurances we were given by British health ministers about the safety of eating beef.   An argumentation-based  theory of dynamic epistemology in public policy would therefore need to include some game theory.   There’s also a close connection to be made to the analysis of the effects of propaganda and counter-propaganda (as in George 1959), and of intelligence and counter-intelligence.
References:
Louise Cummings [2009]: Emerging infectious diseases: coping with uncertainty.  Argumentation, 23 (2): 171-188.
Alexander L. George [1959]: Propaganda Analysis:  A Study of Inferences Made from Nazi Propaganda in World War II.  (Evanston, IL, USA: Row, Peterson and Company).
Marcello Pera [1994]: The Discourses of Science. (Chicago, IL, USA: University of Chicago Press).