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Improving Risk Communication (1989) / Chapter Skim
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2 Understanding Hazards and Risks
Pages 30-53

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From page 30...
... We show how, under such conditions, the judgments of both experts and nonexperts can be affected by preexisting biases and cognitive limitations and how human values and concerns inevitably enter into the analytic process. These factors often lead experts to disagree with each other and with non 30
From page 31...
... Societal choices also involve the benefits associated with hazards and the costs of hazard reduction. Industries that pollute air and water also provide jobs and profits; before requiring pollution controls, public officials usually want to consider the probable effects of the available options on those benefits.
From page 32...
... Thus an area that experiences a severe hurricane once in 200 years faces the same hazard but only one-tenth the risk of a similar area that experiences an equally severe hurricane once in 20 years. The concept of risk makes clear that hazards of the same magnitude do not always pose equal risks.
From page 33...
... These involve calculating separate risk estimates for each hazardous effect, giving heavier weight to qualitative characteristics of risk (e.g., Fischhofl: et al., 1984; Okrent, 1980) and using explicit measures of values and risk attitudes (Regina, 1968~.
From page 34...
... What is the appropriate estimate of harm for highly sensitive populations that bear a significant proportion of the overall risk? What are those populations, where are they located, and what proportion of the total risk do they bear?
From page 35...
... ) ~fonnation on Alternatives The term "risk control assessment" may be used to describe the activity of characterizing alternative interventions to reduce or
From page 36...
... That is, how much would the estimate change if it used different plausible assumptions about exposures or incidences of harm (or benefits) or different methods for converting available data into
From page 37...
... Formation on Management "Risk management" is a term used to describe processes surrounding choices about risky alternatives. In common usage, assessments of the risks and benefits of various options are seen as technical activities that yield information for decision makers, whose decisions are called risk management decisions (National Research Council, 1983a)
From page 38...
... Summer In sum, a weiZ-informed choice about activities that present hazards and risks requires a wide range of knowledge. It depends on understanding of the physical, chemical, and biological mechanisms by which hazardous substances and activities cause harm; on knowIedge about exposures to hazards or, where knowledge is incomplete, on analysis and modeling of exposures; on statistical expertise; on knowledge of the economic, social, esthetic, ecological, and other costs and benefits of various options; on understanding of the social values reflected in differential reactions to the qualities of risks; on knowledge of the constraints on and responsibilities of risk managers; and on the ability to integrate these disparate kinds of knowledge, data, and analysis.
From page 39...
... For activities or substances whose hazards are delayed in onset (such as possible causes of cancer or birth defects) and for substances to which people are exposed in very small quantities, it is Circuit to connect effects to causes.
From page 40...
... . Thus some substances that do not cause cancer or birth defects in test species appear to have these harmful effects on humans.
From page 41...
... For these reasons exposures are usually estimated from data on releases of hazardous substances. Inferring exposures requires numerous assumptions about the transport, dispersion, and transformations of substances, many of which are based on incomplete theory and limited evidence (National Research Council, 1988a)
From page 42...
... To assess the risk from carcinogens, they commonly use data from laboratory experiments on nonhuman organisms. Adding assumptions about how humans differ from the experimental organisms and about how to extrapolate from the 2-year exposures to high doses usually given to laboratory rodents to the long-term low doses characteristic of natural human exposures, they estimate the human risk.
From page 43...
... It is difficult and sometimes proves impossible to reach a consensual judgment about what the probabilities are, let alone what to do about the attendant risks (see Figure 2.2~. Identification of Synergistic Effects Additional uncertainty in risk estimates exists because exposure to one hazard can affect a person's sensitivity to another.
From page 44...
... Does the existence of multiple sources of uncertainty mean that the final estimate is that much more uncertain, or can the different uncertainties be expected to cancel each other out? The problem of how best to interpret multiple uncertainties is one more source of uncertainty and disagreement about risk estimates.
From page 45...
... , and clinical psychologists see patterns they expect to find even in randomly generated test data (O'Leary et al., 1974~. In interpreting statistics relating the incidence of cancer to occupational exposures to particular chemicals, there is a temptation to interpret a correlation between exposure to a particular chemical and the incidence of a particular cancer as evidence of an effect.
From page 46...
... they receive computergenerated predictions for specific periods prior to making their forecasts, (4) a readily verifiable criterion event allows for quick and unambiguous knowledge of results, and (5)
From page 47...
... Although the net effect of these cognitive tendencies has not been determined, their existence justifies a certain amount of skepticism on the part of decision makers, including individuals, about definitive claims made by risk analysts. INFLUENCES OF HUMAN VALUES ON 1[NOWLEDGE ABOUT RISE Although it is useful conceptually to separate risk assessment and risk control assessment from value judgment, there are many respects in which it is not possible to accomplish the separation in practice.
From page 48...
... Different risk analysts have used different summary statistics to represent the risk of death from an activity or technology.3 Among the measures used are the annual number of fatalities, deaths per person exposed or per unit of time, reduction of life expectancy, and working days lost as a result of reduced life expectancy. The choice of one measure or another can make a technology Took either more or less risky.
From page 49...
... It is traditional among civil engineers, public health professionals, and others to take account of uncertainty by being "conservative" in stating risk estimates. This means that they leave a margin for error that will protect the public if the actual risk turns out to be greater than the best currently available estimate.
From page 50...
... The central point here is that either way of representing uncertainty embodies a value choice about the best way to protect public health and safety. These few examples show how human values can enter into even apparently technical decisions in risk analysis, such as about the choice of a number to summarize a body of data.
From page 51...
... A growing body of knowledge on what is usually called "risk perception" helps illuminate the values involved in the evaluation of different qualities of hazards.4 In studies of risk perception individuals are given the names of technologies, activities, or substances and asked to consider the risks each one presents and to rate them, in comparison with either a standard reference or the other items on the list. The responses are then analyzed, taking into account attributes of the hazards and benefits each technology, activity, or substance presents (Table 2.1 lists several such attributes)
From page 52...
... An important implication of such findings is that those quantitative risk analyses that convert all types of human health hazard to a single metric carry an implicit value-based assumption that all deaths or shortenings of life are equivalent in terms of the importance of avoiding them. The risk perception research shows not only that the equating of risks with different attributes is value laden, but also that the values adopted by this practice differ from those held by most people.
From page 53...
... 4. The term "risk perceptions is put in quotation marks because, as the discussion shows, this body of research is more accurately described as the study of human values regarding attributes of hazards (and benefits)


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