Risk assessment provides only part of the information that risk managers use--with information about public values, statutory requirements, court decisions, benefits, and costs--to make decisions about the need for and methods of risk reduction. Different regulatory goals have engendered different definitions of negligible and unacceptable risk and different roles for risk assessment to play in risk-management decision-making. Risk assessment can provide a valuable framework for setting environmental, health, and safety regulatory priorities and for allocating resources within regulatory agencies. Technical risk assessments seldom set the regulatory agenda, however, because of the different ways in which the nontechnical public perceives risks.

This section examines some of the issues that have arisen as the use of risk assessment in regulatory decision-making has evolved and matured. Characterizing risk and communicating information about risks to affected parties have become complex and confusing. Decisions about how to allocate resources to reduce risks can be made partly on the basis of risk comparisons. The use of "bright lines", benchmarks to distinguish negligible from unacceptable risks, has led to questions about what those lines should be, who should decide what they should be, and which situations they should be applied to. Moving from command-and-control regulation to nonregulatory approaches to risk reduction can increase both efficiency and effectiveness. Peer review of the technical, scientific, and economic information that underlies risk-management decisions can help ensure reasonable, supportable decisions. Judicial review is a common element in major regulatory actions. This section offers recommendations on each of those issues in the hope of contributing to the evolution and improvement of risk-based decision-making.

Risk communication engages both the communicator and the audience in listening and in explaining information and opinions. Effective risk communication requires effective risk characterization. Risks have sometimes been communicated to the nontechnical public as single numerical estimates, which are easily misinterpreted and misused. Effective risk communication must involve much more than numeric estimates. Risk communication should include clear messages about the nature, severity, and likelihood of risk and other messages, not strictly about risk, that express concerns, opinions, or reactions to risk messages (NRC 1989). Congress has considered various proposals to increase the transparency of risk assessments and to require the use of risk comparisons. Transparency is generally equated with revealing and characterizing the assumptions, uncertainties, default factors, and methods used to estimate risks. Requiring risk comparisons would compel agencies to compare a risk to be regulated with other risks also regulated by the agency and other risks experienced by the public. This section discusses communicating about risk in the risk characterization stage of the risk assessment and other risk communications with the public, including the use of risk comparisons. Section 5.2 discusses comparative risk assessment for risk management, the process of comparing and ranking risks to identify priorities and make resource allocations.

FINDING 5.1.1: Risk characterization is the primary vehicle for communicating health risk-assessment findings. Many risk characterizations have relied primarily on quantitative estimates of risk to communicate risk-assessment findings. Often they convey an unwarranted sense of precision while failing to convey the range of scientific opinion. They are particularly difficult for nontechnical audiences to comprehend. Without effectively communicating information about who is at risk, how they might be affected, what the severity and reversibility of an adverse effect might be, how confident the risk assessors are about their predictions, and other qualitative information that is critical to decision-making, effective risk management is impeded. Risk management is also complicated by the question of how much information is enough. A practical process is needed for determining when risks have been sufficiently well characterized to reach a decision and to justify it.

RECOMMENDATION: Risk characterizations must include information that is useful for all parties participating in a risk-management decision-making process. Quantitative estimates of risk are important and should be included, but qualitative information on the nature of adverse effects and the risk assessment itself is likely to be most useful. Information on the range of informed views and the evidence that supports them also should be shared. During the problem-formulation stage of a risk-management process, participants should agree on criteria for the value of acquiring additional information so that endless data-gathering does not become primarily an instrument for delaying or obstructing a decision or increasing costs.

RATIONALE

Risk assessment is an uncertain process that requires both scientific data and science-based assumptions. Risk assessments are conducted to infer risks below the range of observable events in people or in studies of laboratory animals. For example, 10-100% of laboratory animals exposed to a relatively high dose of a carcinogen throughout their lives might develop cancers, but regulatory agencies are expected to protect populations from exposure to doses of chemicals that might pose a risk of up to one in a million, not one in 10. The impact of a one-in-a-million cancer risk on a population cannot be detected or measured, because one-fourth of that population is already expected to die of cancer, even in the absence of a particular chemical exposure (see page 3-1). As a result, estimates of small risks are speculative; they cannot be verified. Expressing a small risk solely in numerical terms, especially in single numbers, is misleading and falsely conveys accuracy.

Communicating quantitative information about noncancer risks poses a different challenge because they are not expressed as numerical risk estimates. Noncancer risk is determined by comparing a human exposure to a dose that is considered to be a "safe" standard concentration; that is, exposure to a dose below that standard is considered unlikely to present any risk and exposure just above that standard might be less safe. The quantitative likelihood that adverse effects will occur at exposures above the standard but below exposures observed to cause adverse effects is generally not known. Using a margin-of-exposure approach to cancer risk assessment instead of current methods would result in similar nonprobabilistic expressions of risk (see section 3.1).

More useful and understandable than speculative quantitative estimates of risk is qualitative information. Qualitative information includes a careful description of the nature of the potential health effects of concern, who might experience the effects under different exposure conditions, the strength and consistency of the evidence that supports an agency's classification of a chemical or other exposure as a health hazard, and any means to prevent or reverse the effects of exposure. Qualitative information also includes the range of informed views about a risk and its nature, likelihood, and strength of the supporting evidence. For example, if an agency considers a substance likely to be a human carcinogen on the basis of studies of laboratory animals, but there is some evidence that the classification is flawed, both views should be presented. A discussion of that uncertainty would note the several types of evidence that support the substance's classification as a likely human carcinogen and also the contradictory evidence. The discussion might conclude that because the weight of the scientific evidence supports the substance's classification, the agency has chosen to regulate it as a carcinogen in the interest of protecting public health. Useful guidance for including qualitative information in risk characterizations is found in EPA's Guidance for Risk Characterization (EPA 1995a). Effective ways to communicate quantitative and qualitative information about risks are discussed in more detail below.

As discussed in section 3.3 on uncertainty, communicating a range or distribution of risks reflecting uncertainty is likely to be perplexing to risk managers or nontechnical stakeholders, who often want to know from technical staff whether an exposure is safe or unsafe. There will be complex risk questions that require complex quantitative analysis, but today many risk-management issues are unlikely to be illuminated by intricate quantitative analyses of uncertainty. Federal and state contractors have told the Commission that when they perform comprehensive quantitative analyses of risk-related uncertainty or variability, they are ignored or misunderstood. Of course, as quantitative methods to describe uncertainty and stakeholders' understanding and perceptions of uncertainty and risk evolve and mature, quantitative uncertainty analysis might well attain more general usefulness. Meanwhile, resources would be better spent on conducting research to reduce important sources of uncertainty. As Michael Jayjock, of Rohm and Haas Company, testified before the Commission, "Describing uncertainty is good. Reducing it is better."

In contrast, as discussed in section 3.2, we believe that using distributions to reflect the variability in a population's exposure characteristics can be useful now. Nontechnical stakeholders will certainly comprehend that not all members of a population are exposed to identical doses of contaminants, and that different activities are associated with different exposures. For example, information on toxicity standards could be compared to a distribution of a population's exposures like the following, derived using Monte Carlo techniques and exposure data from a hazardous-waste site.

(µg/m³)

If the concentration of a chemical associated with a 10^-5 cancer risk were 80 µg/m³, for example, the risk manager and other decision-makers would see that most of the population is exposed to less than that concentration. The participants might decide that there is no cause for concern or might attempt to identify the characteristics of the segment of the population in the upper end of the distribution and consider risk-reduction options directed at that segment. If the concentration of concern were 20 µg/m³, participants would see that most of the population is exposed to concentrations exceeding that, and would want to implement more extensive risk-management measures directed at the entire population. The participants might also be interested in comparisons of exposures to contaminant concentrations associated with 10^-4 or 10^-6 cancer risks.

Comparing the distribution of a population's exposures to toxicity standards conveys information that is more useful for decision-making than a single point estimate of risk or a hazard index. Priority-setting might not require exposure distributions, but more-refined risk assessments that support decisions with greater regulatory impact would. Comparing the distribution of a population's exposures to a standard or family of standards (see discussion of bright lines in section 5.3) also conveys information to a risk manager that is less complex than a distribution of risks. In contrast with estimated risk levels, exposure standards are concentrations that can be measured; measurements facilitate implementation, evaluation, and compliance. The risk manager and the public can see clearly what the relationship between a protective exposure standard and a particular population's or subpopulation's exposure is likely to be. That information can be used to make decisions about the need for exposure or risk reduction that can be directed at those who are likely to need it most.

A potential barrier to the successful implementation of the Commission's risk-management framework or to the effective use of tiered approaches to risk assessment and priority-setting is conflict over the need for more information. If a simple screening risk assessment performed for the purpose of priority-setting yields results indicating that a particular industrial facility might pose an unacceptable risk, a more refined risk assessment would probably be desired. A more refined risk assessment would require more data than the screening risk assessment, so there would be an incentive for the owner of the facility to generate those data in the hopes that the more refined assessment would show that it does not pose an unacceptable risk. However, if the more refined risk assessment still indicated that the estimated risk is too high, the owner of the facility might decide that collecting even more data would be worth the investment if regulatory action would be deferred. Ellen Silbergeld, representing the Environmental Defense Fund, emphasized in her testimony before the Commission that the greatest barrier to credible risk assessment is the absence of data and that if an iterative approach to risk assessment is required, guidelines are needed for deciding how much information is enough to conclude the process and support a decision. Likewise, Warner North, of Decision Focus, Inc., recommended both incentives for data collection and incentives for speedy risk-management decisions. At some point, continuing to collect and refine will yield considerably diminished returns with respect to improved risk estimation but could effectively stall a risk-management decision that would require capital investment on the part of the facility owner. Before the risk-management decision-making process proceeds, therefore, preferably in the problem-formulation stage, criteria must be established for determining what constitutes enough information. The nature of the criteria will probably be controversial, but some controversy at the beginning of the process is better than a lot of controversy at the end.

FINDING 5.1.2: Stories abound of misunderstandings about risks and risk-reduction proposals. We know very little about how to ensure effective risk communication that gains the confidence of stakeholders, incorporates their views and knowledge, and influences favorably the acceptability of risk assessments and risk-management decisions.

RECOMMENDATION: Regulatory agencies should adopt comprehensive risk-communication programs that emphasize both the learning and explaining activities of communication, provide research on risk-communication messages, train risk managers and others engaged in communicating risk, and include risk-communication funding, objectives, and evaluation in risk-management plans.

RATIONALE

The Commission's risk-management framework (section 2) is built on continuous involvement of stakeholders and respectful learning from them. Effective risk communication is an essential ingredient in the success of that framework, especially in the problem-identification and options stages in the process.

Risk assessors now recognize that a community's response to learning that a local industry has put them at risk through release of pollutants tends to include a sense of outrage that inevitably magnifies their perception of risk. Studies of the differences between technical and nontechnical perceptions of risk have identified many of the factors that contribute to outrage (Sandman 1992). Those factors include involuntary exposures, lack of previous knowledge of the risk, and dread of effects and severe consequences (Slovic 1987). People factor in their perceived personal potential benefit and harm. A growing body of research provides some guidance on communicating risk information effectively, as detailed in a report prepared for the Commission by David McCallum (see appendix A.5 for abstract). Our discussion here is not comprehensive; rather, it is intended to indicate the importance of effective risk communication and the potential for mistakes and misunderstandings.

Risk-communication research suggests that people interpret and use new information in the context of their existing beliefs. People need a basic understanding of the exposure, effects, and mitigation processes relevant to making decisions about a hazardous process. Responding to those needs through risk communication should involve well-tested methods; an untested communication should no more be released than an untested product (Morgan et al. 1992). Risk communication is a two-way street, however--it means both listening and speaking. Risk communicators should learn about the concerns and values of their audience, their relevant knowledge, and their experience with risk issues. Stakeholders might have knowledge of sources and patterns of exposure that risk assessors do not have. That knowledge needs to be integrated into a risk assessment and risk management. The degree to which information provided by stakeholders is incorporated into risk assessment and risk-management decisions may enhance the prospects for trust, a key to effective communication. By listening, risk communicators can craft risk messages that better reflect the perspectives, technical knowledge, and concerns of the audience. Risk communicators must be prepared to explain and answer questions about any specific, relevant tests or surveys done in the community regarding incidences of illness or uptake of pollutants, and not just rely on general models.

Effective communication must begin before important decisions have been made, as emphasized in the Commission's framework for risk management. It can be facilitated in communities by citizen advisory panels, such as those supported by the Superfund program and the Department of Energy. Many corporations work continuously with citizen advisory panels in their communities. For example, in his testimony to the Commission, a representative of Rohm & Haas Company, noted that the citizen advisory panels that the company works with give it a better understanding of the questions and concerns of the community and an opportunity to test its risk-communication messages before using them with the general public. Not all citizen advisory panels develop a trusting relationship with the company they are advising or are trusted by the community of which they are a part.

With the growing use of risk assessments and risk estimates by regulatory agencies, there is a need to increase the public understanding and credibility of such information. Agencies and Congress have emphasized the importance of improving the quality of risk assessments but have given less attention to the need for training and educating risk assessors and risk managers in communicating information about risk. Comprehensive risk-communication programs that stress listening, as well as explaining, need to be established in regulatory agencies. Training risk assessors and risk managers in risk communication and testing risk-communication messages should have as high priority as every other part of the risk-management process. Specific communication objectives, such as awareness and involvement of stakeholders, should be identified in risk-management plans, with appropriate methods for evaluating the effectiveness of communication. The National Research Council made the case in Improving Risk Communication that "risk managers need to consider communication as an important and integral aspect of risk management" (NRC 1989). A forthcoming Research Council report from the Committee on Risk Characterization also will address the role of stakeholders, especially the public.

The art of risk communication is moving from trying to explain risk information to citizens to a building of partnerships between plant managers and nearby residents, between companies and consumers, and between agency risk managers and the public. Although our air, water, and food are considered cleaner and less risky than they were 30 years ago, the fact that many citizens believe that they are at greater risk indicates that risk communication has a long way to go. Investments of time and resources are clearly needed.

FINDING 5.1.3: People make informal judgments about risks every day. Some risks are familiar, even comfortable; others are unfamiliar and can be sources of considerable fear. Different people have different perceptions of the same risks. It is logical and reasonable for people to request comparisons or for Congress to incorporate mandates for risk comparisons in legislation. But some comparisons trigger resentment, as though a substantial risk were being dismissed or belittled.

RECOMMENDATION: Risk comparisons should help to convey the nature and magnitude of a particular risk estimate and should compare risks associated with chemically related agents, with the same agent from different exposure sources, with different kinds of agents with the same exposure pathway, or with different agents that produce similar effects. The margin-of-exposure approach (see section 3.1.1) can be applied to such comparisons across similar and different types of adverse health effects.

RATIONALE

Risk comparisons can be of many kinds. At the simple end of the spectrum are comparisons of magnitude, such as a one-in-a-million cancer risk compared with the length of one inch in 16 miles; comparisons of chemically related agents, such as one organophosphate pesticide with another; comparisons of the same agent with different exposure sources, such as polycyclic aromatic hydrocarbons from moter-vehicle exhaust and from broiled meat; comparisons of different agents with the same exposure pathway, such as carcinogenic components of natural foods and synthetic additives in food; and comparisons of different agents that produce similar effects, such as the risk of lung cancer from radon inhalation and from smoking a particular number of cigarettes. Toward the complex end, multiple risks are compared across a variety of dimensions, such as the hazards of different energy-producing or Superfund cleanup technologies to the public, workers, and ecosystems.

In general, risk comparisons can help people to comprehend probabilities or magnitudes. Most people, including physicians, often cannot easily relate low-risk probabilities or ratios, such as "one-in-a-million," to their everyday experience. One solution is to make quantitative comparisons between familiar and less familiar risks. A better solution might be to use analogies--one-in-a-million is equivalent to 30 seconds in a year, 1 inch in 16 miles, or 1 drop in 16 gallons. Another solution might be to express risk in terms of the number of persons who might be affected per year or per hypothetical 70-year lifetime. Even more difficult to communicate is the fact that a one-in-a-million risk estimate currently is not an estimate of actual risk, but a statistical upper bound on the likelihood that a risk could exist; that is, the actual risk is likely to be much lower, and it could be zero, but it is quite unlikely to be higher.

Many people perceive the reduction of risk by an order of magnitude as though it were a linear reduction. A better way to illustrate orders of magnitude of risk reduction is shown in Figure 5.1, in which a bar graph depicts better than words that a reduction in risk from one in a 1,000 (10^-3) to one in 10,000 (10^-4) is a reduction of 90% and that a further reduction to one in 100,000 (10^-5) is a reduction 10-fold less than the first reduction of 90%. The percent of the risk that is reduced by reducing emissions and exposures is a much easier concept to communicate than reductions expressed in terms of estimated absolute risk levels, such as 10^-5.

Figure 5.1 Reducing risk by orders of magnitude is not equivalent to linear reductions.

A different proposal for communicating risk magnitude is to use time intervals, which might be better understood than numerical probability estimates. Goldstein indicates that converting probabilities per unit of population to periods per event, such as one death expected in 3,500 years, substantially altered the perception of threat (Weinstein et al. in press). The city of Columbus, Ohio, did an analysis indicating that one death would occur in Columbus in 204 years from an additional cancer risk at the theoretical one-in-a-million level, compared with frequencies of several deaths per day or every few days for measurable risks, such as ordinary rates of heart disease, cancer, homicide, and automobile collisions. The mayor of Columbus, Gregory Lashutka, in testimony before the Commission, stated that that analogy helps citizens to understand the magnitude of the effects that any federal or state regulation concerning the environment, transportation, labor, or education might have on the community. We recommend expressing risks as numbers of events in an actual exposed community or on an annual basis, not just per million hypothetical people over a lifetime.

Using comparisons to explain the magnitude of risks will be increasingly important as advances in analytic chemistry improve our ability to detect smaller and smaller amounts of chemicals in air, water, and other media. This phenomenon of a plummeting "nondetectable" level or a "vanishing zero" poses a problem, particularly in the assessment of risks associated with human carcinogens, to which no level of exposure is assumed to be without risk.

Risk comparisons can be helpful, but they should be used cautiously and tested if possible. There are proven dangers in comparing risks of diverse character, especially when the intent of the comparison is seen as minimizing a risk (NRC 1989). One difficulty in using risk comparisons is that it is sometimes difficult to find risks that are sufficiently similar to make a comparison meaningful. In general, comparisons of unlike risks should be avoided; they have often been either confusing or irritating because they were seen as unfair or manipulative. Research on risk perception has suggested that directly comparing voluntary and involuntary risks or natural and technologic risks does not improve understanding of risks. However, comparisons of risks associated with chemically-related agents, risks associated with the same agent with different exposure sources, risks related to different kinds of agents with the same exposure pathway, or comparisons of different agents that produce similar effects can improve communication.

Risk comparisons can either improve or hinder risk communication. Testing messages that use risk comparisons, even informally, can help to avoid miscommunication and misunderstanding.