Scientific uncertainty in advising and advocacy

Abstract Scientific advisory committees and scientific advocacy groups would substantially improve policy decisions and public discussion of issues involving scientific uncertainty, if they were to clearly and honestly distinguish among settled fact, mainstream opinion, legitimate minority opinion, and assertions with no scientific basis. Such a franker treatment of scientific uncertainty would assist scientific advisers to adjust to their newly important role of guiding and framing public discussion. It would increase their credibility and their professional status of scientific advocacy groups, the more so if this were to be part of a broader code of ethics. Decision makers could still base their decisions (and advocacy groups could still base their views) on minority science, but they would be under some pressure to acknowledge that fact to the public. The Inter-Governmental Panel on Climate Change (IPCC) has introduced and applied a probabilistic scale of scientific uncertainty that can be used for this purpose, and the author has proposed an alternative scale based on legal standards of proof. A variety of managerial, political and legal issues depend on the ability of generalists untrained in science to comprehend the science underlying controversy and the degree of uncertainty to which these facts are understood. Of these, climate change stands out, both because of the high economic, political and social stakes that it involves, and for the unusual level of public focus on the level of uncertainty associated with scientific forecasts of the degree of climate change and of its likely economic cost. Even so, it required a major effort before the Inter-Governmental Panel on Climate Change (IPCC), the scientific advisory body with the official responsibility to advise the negotiations on climate change, undertook to establish and put into practice a scale by which it could communicate to policy makers and to the public at large the level of scientific uncertainty it associated with many (but not all) of its assertions [1] . The IPCC scale is based on Bayesian probability, i.e., the odds that an informed bettor would accept that the assertion is valid. The author has proposed a more elaborate scale based on benchmarks taken from standards of proof used in different branches of US law, as a complement to such probabilistic scales, and correlated this with a scale used informally by working scientists. These scales are summarized in Table 1 Table 1 . Scales of scientific certainty Level Bayesian probability (%) IPCC scale Informal Scientific Scale Scale based on legal standards of proof Legal situation where standard of proof applies 10 100 (not in scale) Firmly established, explains a broad range of phenomena “Beyond any doubt” Exceeds criminal standard 9 99 “Virtually certain” Rigorously proven “Beyond a reasonable doubt” Criminal conviction 8 90–99 “Very likely” Substantially proven ”Clear and convincing evidence” Quasi-penal civil actions, such as termination of parental rights 7 80–90 “Likely” Very probable “Clear showing” Granting temporary injunction 6 67–80 Probable “Substantial and credible evidence” Referring evidence for impeachment 5 50–67 “Medium likelihood” “If I must choose, this seems more probable than not” “Preponderance of the evidence” Most civil cases 4 33–50 Evidence is increasing but not preponderant “Clear indication” Proposed as criterion for nighttime, X-ray or body cavity searches 3 10–33 “Unlikely” Plausible, backed by some evidence “Probable cause”, “Reasonable belief” Field arrest; search incident to arrest; search warrant; arraignment or indictment 2 1–10 Possible “Reasonable, articulable grounds for suspicion” Stop and frisk for weapons 1 “Very unlikely” Unlikely “No reasonable grounds for suspicion,” “Inchoate hunch” Does not justify stop and frisk 0 0% (not in scale) Violates well established laws Impossible Action taken could not possibly have resulted in the crime being charged . A full explanation of the background to this table is found in a separate publication by the author [2] . In this article, we explore the institutional implications of this franker and more explicit treatment of scientific uncertainty in a variety of situations in which the level of scientific uncertainty associated with a given assertion must be conveyed to an audience untrained in science. We shall argue that the general acceptance of the need for a more explicit treatment of scientific uncertainty would ease a number of desirable institutional evolutions: from private scientific advisers into framers of public debate, and from free-wheeling scientific advocates into a recognized profession with clearly articulated professional ethics.