A couple of comments on the topic, as discussed in this string:

1) References

a) Several pertinent references on the communication/understanding
angle, although not directed at natural hazards specifically, appear
in two papers of my own:

Johnson, B.B. and P. Slovic (1995). "Explaining uncertainty in health
risk assessment:  Initial studies of its effects on risk perception
and trust," Risk Analysis, 15, 485-494.

Johnson, B.B. and P. Slovic (1998). "Lay views on uncertainty in
environmental health risk assessment," J. of Risk Research, 1,
261-279.

b) A somewhat old reference is Nigg, J.M. (1982). "Communication under
conditions of uncertainty:  Understanding earthquake forecasting," J.
of Communication, Winter, 27-36.  A survey experiment involving
communication of uncertainty in hurricane landing forecasts in Florida
is Earl J. Baker, "Public Response to Hurricane Probability Forecasts,"
The Professional Geographer, 47 (2) pp. 137-147, 1995.

c) There is an extensive literature on how people react to different
forms of presenting quantitative estimates of uncertainty.  See
Slovic, P., J. Monahan, and D.G. MacGregor (2000), "Violence Risk
Assessment and Risk Communication:  The Effects of Using Actual Cases,
Providing Instruction, and Employing Probability Versus Frequency
Formats," Law and Human Behavior, 24, 271-296 for one of the more recent
examples.

d) Although not directly related to the issue of communication, I
would recommend for its thought-provoking content Smithson, M. (1989).
Ignorance and Uncertainty:  Emerging Paradigms. New York:
Springer-Verlag.  A more recent review, which I have not yet read, is
van Asselt [possibly van Hasselt--my source is unclear], M.B.A. (2000).
Perspectives on Uncertainty and Risk.  Boston/ Dordrecht:  Kluwer.

2) I would caution that quantitative estimates of uncertainty made by
experts are not the only, or even the most important, issues with
regard to risk management, for natural hazards or other risk topics.
This is not to deny the value of the topic for research or seminar
presentations, but to suggest (for example) that studies manipulating
only this element may mis-estimate its impact on hazard management by
either citizens or officials.  For example, one might consider the
impact of such estimates relative to:
a) qualitative estimates of uncertainty, by experts or others
b) uncertainty about topics highly relevant to hazard management, but
not concerning risk estimates (e.g., do officials know what they're
supposed to do to prevent/mitigate hazard consequences? will they
actually do these things?)
c) factors that have nothing to do with uncertainty (except perhaps,
in some cases, as means to reduce uncertainty to acceptable levels),
but
may swamp effects of the communication or size of uncertainty in risk
estimates:  trust in communicators/hazard managers; ideology; beliefs
about flood consequences, carcinogenicity, etc.  (Uncertainty may
sometimes be used as a rationale for particular actions or lack of
action--e.g., failure to evacuate after a hazard warning--but that
isn't a demonstration that manipulation of the level or presentation
of
uncertainty has a stronger effect than, say, desire to evacuate as a
family group.)

After some 30 years of research on technological risk "perception"/
communication, and even more on natural hazards, these statements
should be unexceptional.  But the slim literature on uncertainty
suggests
that few empirical studies actually take these other factors into
account.

3) Regarding Ilan Kelman's reprise of the Newhall and Hoblitt paper:

I have not read this paper, but many of the themes raised about the
constraints/dangers of risk comparisons seem reminiscent of those
raised by Covello, V.T., P.M. Sandman, and P. Slovic (1988). Risk
Communication, Risk Statistics and Risk Comparisons:  A Manual for
Plant Managers (Washington, D.C.:  Chemical Manufacturers Association).

Many of these points are sound, such as variability in audience
response
(also mentioned in Ben Wisner's message on the U. of Liverpool seminar
series), as noted in my forthcoming paper (below).  However, I would
caution that the empirical work in this area is very scanty.  In the
field of technological/environmental risk (which I know best), the
scholarly response seems to have been divided between natural
scientists' and engineers' insistence (without evidence) that risk
comparisons are ideal for "putting risks into context"--as in the Wilson
and Crouch tradition--and satisfaction among social and behavioral
scientists that Covello et al. proved that such comparisons are
counter-productive and a trivial topic not worth research.
Unfortunately for the latter, Covello et al. in fact provided no
empirical evidence for their arguments (e.g., about which kinds of risk
comparisons might be more acceptable to the public), and one of the
authors acknowledged to me a few weeks ago that these  arguments were
drawn up in a weekend's worth of brainstorming.

The slim empirical research base since then suggests caution and
careful pre-testing are still very much in order, but that (a) the
cautions might not be quite the same ones proposed by Covello et al.,
and (b) it's not clear that comparisons have a major impact on (public)
audiences' beliefs about hazards.  Since this is not the primary topic
of the initial posting, I won't go into detail here, but suggest that
putting risks into context--whether uncertainty is conveyed or not--is a
communication task that scholars have yet to plumb in any depth, much
less be able to offer good advice to practitioners.  The following
references are FYI:

Roth, E., M.G. Morgan, B. Fischhoff, L. Lave and A. Bostrom (1990).
"What Do We Know About Making Risk Comparisons?," Risk Analysis, 10,
375-387.

Slovic, P., N. Kraus, and V.T. Covello (1990). "What Should We Know
About Making Risk Comparisons?," Risk Analysis, 10, 389-392.

Freudenburg, W.R. and J.A. Rursch (1994). "The Risks of 'Putting the
Numbers in Context':  A Cautionary Tale," Risk Analysis, 14, 949-958.

Sandman, P.M., N.D. Weinstein, and P. Miller (1994). "High Risk or
Low: How Location on a 'Risk Ladder' Affects Perceived Risk," Risk
Analysis, 14, 35-46.

Johnson, B.B. (1999). "Risk Comparisons in a Democratic Society:  What
People Say They Do and Do Not Want," Risk:  Health, Safety &
Environment, 10, 221-230.

Johnson, B.B. (2002). "Comparing Bottled Water and Tap Water:
Experiments in Risk Communication," Risk:  Health, Safety &
Environment, 13, 69-94.

Johnson, B.B. (2002). "Stability and Inoculation of Risk Comparisons'
Effects Under Conflict:  Replicating and Extending the 'Asbestos Jury'
Study by Slovic et al.," Risk Analysis, 22, 777-788.

Johnson, B.B. (forthcoming 2003). "Are Some Risk Comparisons More
Effective Under Conflict?:  A Replication and Extension of Roth et
al.," Risk Analysis.

Branden B. Johnson, Ph.D.
Bureau of Risk Analysis
Division of Science, Research and Technology
New Jersey Department of Environmental Protection
P.O. Box 409
401 East State Street
Trenton, NJ 08625-0409
U.S.A.
609-633-2324
609-777-2852 fax
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